HEMOGLOBIN, l(7).
679-690 (1977)
BINDING OF PROTOPORPIIYRIN TO tlEMOGLOBIN IN RED BLOOD
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CELLS OF PATIENTS WITH ERYTHROPOIETIC PROTOPORPHYRIA
J. van Steveninck, T.H.A.R.Dubbelmnn, A.F.P.M. de Coeij and L.N. Went Sylvius Laboratories Laboratory for Medical Chemistry and Department of Human Genetics Wassenaarseweg 72 Leiden, The Netherlands
Abstract Virtually all protoporphyrin in erythrocytes of patients vith erythropoietic protoporphyria is bound to hemoglobin. The maximum of the fluorescence excitation spectrum of this protoporpliyrin-hemoglobin complex shifted, with increasing concentration, from 405 nm to 389 nm. A similar shirt was observed wlien titrating a solution of free protoporphyrin with hemop;lobin. The Soret maximum of free protoporphyrin itself. on the other hand, was not concentrationdependent. These observations indicate that spectrofluorometric measurements do not allow conclusions coticerning the mode of protoporphyrin binding to hemoglobin. Experiments on protoporphyrin exchange between the hemoglobins A , F and S reinforced the previously drawn conclusion that protoporphyrin is bound to hemoglobin at the heme-binding sites.
Introduction The protoporpliyrin concentration in red blood cells of patients with erythropoietic protoporphyria (EPP) is invariably increased. This
679 Copyriplit 0 1977 hy Marcel I k k k c r . lnc A l l Rielits Rrrctvrd Nrilhcr I h i q work nor any p:trl may hc reproduced or Iransniillcd in any h r r n o r hy any nicafts. rlrrtronic or nicchanical. inclucltny . hy any infnrninlitin slorafic arid rrltievai Sy5lCni. photocopying. microfilming. and 1 ~ ~ 0 r d t t 1 por without permission in writins front the puhlirlter.
680
VAN STEVENINCK
ET AL.
is caused by a genetically determined decrease of heme synthetase activity (1-4) in the final stage of erythroid.development ( 1 ) . The accumulated protoporpliyrin is bound to hemoglobin inside the cells (5.6).
We concluded. based on isoelectric focusing and
protoporphyrin-hemoglobin binding experiments, that protoporpliyrin
was bound at the heme-binding sites (5).
Spectrofluorometric mea-
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surements, on the other hand, seemed to indicate a protoporpliyrin binding at sites other than the heme-binding sites (6).
In view
of this apparent contradiction, this problem was reinvestigated. Measurements of absorption spectra of hemoglobins and of fluorescence excitation spectra of protoporphyrin and of hemolysates of red blood cells of EPP patients showed that the spectral data should be explained in a way different from that proposed by Lamola et al. (6). The interpretation of the spectral data presented in this paper does not contradict a binding of protoporphyrin at the heme-binding sites of hemoglobin. The protoporphyrin-lirmoglobin binding experiments were extended with protoporpliyriii exchange measurements between adult hemoglobin A, fetal hemoglobin and sickle cell hemoglobin S. These experiments corroborated the conclusion that protoporphyrin binds at the heme-binding sites of hemoglobin. Methods Freshly drawn heparinized human blood was centrifuged and uastied with buffered isotonic NaCl solution shortly after collection.
Hemolysis was evoked by mixing one volume of washed red
blood cells with two volwiies of distilled water.
The soluble cell
fraction was obtained by centrifugation at 48,000 X g during 30 min at 4OC.
Hemoglobin concentrations were measured according
to Crosby et al. (7).
Conversion of hemoglobin to hemiglobin
(methemoglobin) was accomplished uith K3Fe(CN)6.
as described by
Bunn and Jandl ( 8 ) . Electrophoretic separation of hemoglobins was done in starch gels, as described previously (5).
Protoporphyrin was extracted
BINDING OF I'ROTOPORPIIYRIN
TO ILEMOCLOBIN
681
from the gels according to Schwartz et al. ( 9 ) aEter homogenizing the gel in a Potter apparatus.
The protoporphyrin concentration
was measured fluorometrically. Light absorption spectra were measured on a Beckmann D . B . spectrophotometer.
Fluorescence excitation spectra were recorded
on a Aminco-Bowman spectrophotofluorometer.
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Results The fluorescence excitation spectrum of the soluble cell fraction of EPP red blood cells at two different dilutions is shown in Fig. I.
Apparently the Soret maximum is concentration-
dependent: with increasing concentration the maximum shifted to a lower wavelength.
Tlie maximum at 315 nm, on the other hand, did
not show a concentration-dependent shift.
The relationship be-
tween concentration and Soret maximtim is shown in Fig. 2. The fluorescence excitation spectrum of pure protoporphyrin dissolved in buffered isotonic NaCl solution exhibits maxima at
405 and 315 nm.
The wavelength of these maxima appeared to be
independent of the protoporphyrin concentration.
If, Iiowever,
increasing amounts of hemoglobin were added to the protoporphyrin solution, a gradual shift of the Soret maximum to lower wavelengths was observed again.
At lov concentrations hemiglobin
provoked a similar shift of the Soret maximum.
With increasing
concentrations of hemiglobin this shift to lower vavelcngtlis continued, whereas concomitantly a second maxinnim appeared at about 420 nm (Fig. 3).
These phenomena can be explained from the fluorescence excitation spectrum of protoporphyrin and the absorption spectra of hemoglobin and hemiglobin.
As shovn in Fig.
4, the Soret band
of pure protoporphyrin, dissolved in buffered isotonic NaC1, extends from 340 to 450 nm, vith a maximum at 405 nm.
The absorp-
tion spectra o f hemoglobin and hemiglobin cover this excitation spectrum to a considerable degree. but not completely. hemoglobin absorbs strongly.
At 405
nm
At 390 nm the fluorescence excita-
VAN STEVENINCK ET AL.
682
0,
u 100 C at u
:80 In
Hemoglobin Downloaded from informahealthcare.com by University of Otago on 12/26/14 For personal use only.
3
60
40
20
I
I
300
3 50
I
I
LOO 150 excitation wavelength, nm
FICUKE I
Fluorescence excitation spectrum (for fluorescence at 6 2 5 nm) of the soluble cell fraction of EPP red blood cells diluted I :20,000 (-1 and I : 2,000 (----) respectively. Fluorescence is expressed i n arbitrary units.
tion efficiency is about 86% of that at 405 nm.
The absorbance of
hemoglobin at 390 nm, however, is only 45% of its absorbance at
405 nm.
Therefore, vith increasing hemoglobin concentrations,
fluorescence excitation at 405
NU
will be strongly quenched,
whereas fluorescence excitation at 390
NIL
will be much less
quenched. Thus, at sufficiently high hemoglobin concentrations, fluorescence excitation will be more effective at 390 nm than at
BINDING OF FROTOPORPlIYRIN TO HEMOGLOBIN
683
E
E’
.-
X
Hemoglobin Downloaded from informahealthcare.com by University of Otago on 12/26/14 For personal use only.
402
394
386t
, \
40
*
,
,
,
80
120
160
200
5
dilution factor x10 FIGURE 2
Relationship between the Soret maximum and the concentration of the liemolysate of EPP erythrocytes.
,405 nm.
This inner filter effect of hemoglobin explains the
gradual shift of the protoporpliyrin fluorescence excitation maximum to lower wavelengths witti increasing hemoglobin concentrations (Figs. 1 and 2). The appearance of a second peak at 420 nm after addition of hemiglobin can be similarly explained.
The absorbance of hrmi-
globin drops much faster between 4 0 5 and 4 2 5 nm than the absorbance of hemoglobin (Fig. 4).
The fluorescence excitation efficiency at
420 nm is about 6OX of the efficiency at 405 nm, whereas the ab-
VAN STEVENINCK ET AL.
684 Q,
C
100
0,
u
ln
E0
= 80 Hemoglobin Downloaded from informahealthcare.com by University of Otago on 12/26/14 For personal use only.
3
60
LO
20
1
I
350
300
I
I
LOO L50 excitation wavelength. nm
FlCURF, 3
Fluorescence excitation spectrum of 1.6 pH protoporphyrin in isotonic NaC1, pll 7.4. control; : 4 ubl hemiglobin added; : 8 VM hemiglobin added; -*-*: 16 uM hemiglobin added.
..--
- .-
----
sorbance of hemiglobin at 420 nm is only 302 of that a t 405 MI. Thus, using similar lines of reasoning, one could anticipate the appearance of a new peak around 420 nm at increasing hemiglobin concentrations. This interpretation of the results was confirmed by measurements of the fluorescence excitation spectrum of protoporphyrin. while a second cuvet containing varying concentrations of hemoglobin or hemiglobin was placed in the pathway of the exciting
BINDING OF PROTOPORPHYRIN TO IIEMOGLOBIN
$100
685
-
C 0
e0
In D
-
0
80
-
60
-
40
-
20
-
0)
u
C
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Q,
0 ul
o,
L
0 3
.c
L
I
1
I
FIGURE 4 Absorption spectra of hemoglobin (----) nnd liemiglobin ( . * . * ) fluorescence excitation spectrum of protoporpliyrin (-).
light beam.
and
Exactly the same shifts of the fluorescence excitation
maximum were observed, even though the protoporphyrin and the hcmoglobin were spatially separated. I n further experiments stroma-free hemolysate of EPP red blood
cells was mixed with hemoglobin F and hemoglobin S respectively. The mixtures were incubated during 3 hours at 37OC. Subsequent starch gel electrophoresis yielded the results schematically The parts of the gel vhere the different
depicted in Fig. 5, a-c.
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686
3
VAN
STEVENTNCK ET AL.
I I
FIGURE 5 S t a r c h g e l e l e c t r o p l i o r e s i s of liemolysate of EPP r e d c e l l s i n c u b a t e d a l o n e ( a and d ) , v i t h hemoglobin S (b and e ) and w i t h henloglobin F (c and f ) . I n a - c t h e i n c u b a t i o n s vere c a r r i e d o u t v i t h o u t pretreatment. In d f t h e hemoglobins vere c o n v e r t e d i n t o hemiglobins p r i o r t o incubation.
-
hemoglobin f r a c t i o n s were o b s e r v e d were c u t o u t and a s s a y e d f o r protoporphyrin.
No p r o t o p o r p h y r i n exchange o c c u r r e d : a l l p r o t o -
p o r p h y r i n was r e c o v e r e d a t t h e p o s i t i o n of hemoglobin A , d e r i v e d from t h e EPP r e d blood c e l l s .
I f t h e hemoglobins v e r e c o n v e r t e d t o
hemiglobin p r i o r to mixing and i n c u b a t i o n . t h e e l e c t r o p h o r e s i s p a t t e r n shovn i n F i g . 5 , d - f . was o b t a i n e d .
Under t h e s e citcum-
s t a n c e s p r o t o p o r p h y r i n was exchanged between t h e hemiglobin A of t h e EPP p a t i e n t and hemiglobins F atid S r e s p e c t i v e l y .
The amount
6R7
B I N D I N G OF PROTOPORF'HYRLN TO IIEFIOCLOBIFI
o f p r o t o p o r p l i y r i n found iii t h e d i f f e r e n t IiemiRlohin f r a c t i o n s was p r o p o r t i o n a l t o t h e r e l a t i v e amount of t h e + e F r a c t i o n s . i n d i c a t i n g a 1002 exchanRe a c c o r d i n g t o t h e c a l c u l a t i o n s Riven
hy Bcinn and
J a n d l (8). Discussion
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P r o t o p o r p h y r i n , a c c u m u l a t e d i n e r y t h r o c y t e s of EPP p a t i e n t s .
is hound t o hemoglobin ( 5 . 6 ) .
Lamola e t a l . ( 6 ) found a f l i i o r e s -
c e n r e e x c i t a t i o n maximum o f l i e m o l y s a t e s d e r i v r d from EPF r e d b l o o d
c e l l s a t 397 nm.
P r o t o p o r p h y r i n i n c u b a t e d w i t h henloRlohin A had a
maximrim a t ttie same wavelenRtli. w h e r e a s p r n t o p o r p h y r i n i n c u b a t e d w i t h g l o h i n showed a maximum a t 4 0 3 nm.
T h e s e d a t a were i n t e r -
p r e t e d as i n d i c a t i n g a s t r i i c t c i r a l d i f f e r e n c e hetween t h e Iieninlysate
of EPP r e d b l o o d c e l l s and the. protoporpliyrin-liemoglohin A complex on tlie o n e hand and t h e p r o t o p o r p h y r i n - R l o h i n Since i n t h e protoporphyrin-glohin
romplex on ttie o k h e r .
complex tlie p r o t o p o r p h y r i n
b i n d i n g occurs a t t h e heme-hinding s i t w (10- 1 2 ) .
i t waq s u g R e s t e d
t h a t b o t h i n t h e protoporphyrin-hemoRLobin A complex and i n t h e t i e m o l y s a t e o f EPP r e d b l o o d c e l l s tlie h i n d i n 8 r i r r r i r r r d a t n t l i e r
sites.
T h i s i n t e r p r e t a t i o n i s r e f u t e d hy t h e r e s u l t s p r e s e n t e d i n
t h i s paper.
As h a s been shown. t h e f l u o r e s c e n c e e x c i t a t i o n maxi-
mum o f b o t h t h e h e n m l y s a t e o f EPP r e d blood c e l l s and t l i r p r o t o porpliyrin-liemoy,lobin
A complex i s c o n c r n t r a t i n n - d e p e n d e n t .
t h e i n n e r f i l t e r e f f e c t of hemoglobin. measured by Lamola e t a l . ( 6 ) a t
R
due t o
The maxinium a t 397 nm was
d i l u t i o n of ahoiit I : 2.000.
T h i s a g r e e s w i t h t h e r e s u l t s p r e s e n t e d i n FiR. 2 .
I t cnn b e i n f e r -
r e d t h a t t h e s e s p e c t r o f l u o r o n i e t r i c measurements do n o t a l l o w conc l u s i o n s c o n c e r n i n g tlie mode o f p r o t o p o r p h y r i n b i n d i n g to hcmoglobin. I n a p r e v i o u s p a p e r i t was c o n c l u d e d t h a t i n El'P
rcd blood
c e l l s tlie p r o t o p o r p h y r i n i s bound t o liemoglohin a t t h e heme-bindin8 sites (5).
T h i s was b a s e d o n t h e f o l l o w i n g o b s e r v a t i o n s .
notti
w i t h i s o e l e c t r i c f o c u s i n g and w i t h s t a r c h g e l e l e c t r o p h o r e s i s of hemolyzed EPP e r y t h r o c y t e s t h e p r o t o p n r p h y r i n was r e c o v e r e d a t t h e
VAN STEVENLNCK E T AI..
688
p o s i t i o n of heiiwglobin. M i x t b r e s of p r o t o p o r p h y r i n and hemoglobin gave q u i t e d i f f e r e n t r e s u l t s . With i s o e l e c t r i c f o c u s i n g t h e prot o p o r p h y r i n moved i n t o tlie anode s o l u t i o n and w i t h s t a r c h g e l e l e c t r o p h o r e s i s i t s t r e a k e d froin t h e a p p l i c a t i o n l i n e i n tlie d i r e c t i o n of tlte anode. These r e s t i l t s r e v e a l e d a n e s s e n t i a l d i f f e r e n c e between ttie p r o c o p ( ~ r p l i y r i i i - l i e i i i ~ g l o b i icomplex i p r e s e n t i n EPP red
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blood c e l l s and tlie coinl1Irx formed by i n c u b a t i o n of p r o t o p o r p h y r i n with normal Iirinoglobiii. 'llie e x i s t e n c e of t h e l a t t e r complex can be demonstrated by g e l f i l t r a t i o n on Sephadex G 100. w i t t i hemoglobin and p r o t o p o r p l i y r i n e i t i t i n g i n tlie same f r a c t i o n w i t h an a p p a r e n t m o l e c u l a r weight o f a b o u t , 70,000 d a l t o n s . T h i s complex i s d i s r u p t e d , Iiowever, by e l e c t r i c a l f o r c e s b o t h d u r i n g i s o e l e c t r i c f o c u s i n g and s t a r c h e l e c t r o p h o r e s i s , wliereas tlie complex, p r e s e n t i n EI'P r e d blood c e l l s is s t a b l e under Lliese c i r c u m s t a n c e s . A f t e r i n c u b a t i o n o f p r o t o p o r p h y r i n w i t h liemiglobin, however, a protoporpliyriii-liemiglobin complex i s fornied w i t h ~ l i rsame c l i a r a c t e r i s t i c s a s t h e p r o t o p o r p h y r i n hemiglobin coniplex d e r i v e d froiii EPP e r y t h r o c y t e s , b o t h w i t t i r e f e r e n c e t o i s o e l e c t r i c f o c u s i n g and t o s t a r c h g e l e l e c t r o p h o r e s i s (5). S i n c e t h e f e r r i h e n i e grotip is mcich l e s s f i r m l y bound t o g l o b i n tlian t h e normal heme group ( 8 . 1 3 ) .
these r e s u l t s indicate that a
spontaneous replacement of Iiemt! by p r o t o p o r p h y r i n does not t a k e p l a c e . whereas p r o t o p o r l ) l i y r i n - f ~ r r i h e m e exchange can o c c u r r e a d i l y . The roncliisioii t h a t i n EPP red blood c e l l s p r o t o p o r p h y r i n is bowid t o hcinoglobin a t t h e heme-binding s i t e s i s r e i n f o r c e d b y t h e e x p e r i m e n t a l r e s u l t s o u t l i n e d i n F i g . 5. A f t e r e l e c t r o p l i o r e s i s of a liemolysate of EPP e r y t h r o c y t e s L l i e p r o t o p o r p l i y r i n was r e c o v e r e d a t ttie p o s i t ' i o n of Iienioglobin A . No exchange of p r o t o p o r p t i y r i n between tlie hemoglobin A aiid hemoglobin F o r S took p l a c e d u r i u g p r e i n c u b a t i o n . A f t e r coiiversion t o h e m i g l o b i n , however, 100%exchange of p r o t o p o r p h y r i n occur.rcd. b o t h i n t h e hemiglobin Ahemiglobin F and i n tlie hciaiglobin A
-
hemiglobin S m i x t u r e . The
most obvious i i i t e r p r e L d t i o n a g a i n is t h a t protoporpliyritl is bound a~ heme-binding
s i t e s of tlte Ireinoglolin m o l e c u l e s . 'The experimen-
t a l r e s u l t s can t h e n he r a t i o n a l i z e d on t h e b a s i s of n o exchange
between p r o t o p o r p l i y r i n and Lhe s t r o n g l y bound heiiie group and a
BINDING O F PROTOPORPIIYRIN TO HMOG1,OBJN
689
rattier easy exctianre hetween protoporpltyrin arid ilie l o o s e l y hotlnd
f err i heme grotip. W l t m irradiated witti visihle light red I>lood rrlls from patients
with EPP readily 1tc.molyze. a s a consequence o f prntnporpltyrin-iridtlced pltotodyriamic memhrnnt- danmpe ( 1 4 ) . The descrihcd binding of protoporpttyrin to hemoglohin is not
iii
contradiction wit11 this observation.
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The photodynamic process is mediated via the formation of singlet oxygen (15). A s pointed out b y Krinsky (16) this singlet oxygen can dirfose over relatively great distances in biological systems. before being qriencltetl.
Acknowledgement Ttie authors are much indebted to Karnti Cltristianst- f o r her ski1 ful technical assistance. References De Coeij, A.F.P.M., Cliristianse, K. and Van Steveninck. J . . Europ. J . Clin. Invest.. 5: 397, 1975. 2. Bloomer, J . R . , Bonkovsky, A.L., Ebert. F.S. and Malioney. M.J., Lancet, 226, 1976. 3. Bottomley. S.S., Tanaka. If. and Everett. M . A . . J . Lab. Clin. Med., 2 : 126, 1975. 4. Bonkovsky, H.L., Bloomer. J.R., Ebert, P.S. and Malioney, M.J.. J . Clin. Invest.. 5 G : 1139, 1975. Van-Steveninck, J . arid Went, L.N.. Clin. 5. De Goeij, A.F.P.M., Chim. Acta, 6 3 : 355. 1975. 6 . Lamola, A . A . , P i z e l l i , S., Poll-Fitzpatrick, F 1 . U . . Yamnne. T. and Ilarbcr, L.C.. .I. Clin. Invest., 56: 1528. 1975. 7. Croshy. W . H . , Munn. J. I. and Furth, F.W., U.S. Armed Forces Med. J . , 5 : 6 9 3 , 1954. : 4 6 5 . 1968. 8. Biinn, H.F. a n z Jandl, J . H . , J . Biol. C l i r m . , Bossenmaier. I. and Dinsmore, H., 9. Schwartz, S., Berg, M.11.. in: Methods of Biocliemical Analysis, vol. 8. edited by D. GLick, page 221. Interscience Publishers Inc.. New York. 1960. 10. Leonard, J . J . , Yonetani, T. and Callis, J . U . , Biocliemistry. 13: 1460, 1974. I t . RossFFanelli. h . . Antonini. E. and Caputo, A . , Biochim. Biopliys. Acta 35 : 93, 1959. 12. Treffry, A . and AiGworth. S., Biochem. J. 137 : 319. 1974. 13. Schulman. H.M., Martinez-Medellin, J . and Sidloi. R . . Biochem. 5 : 220, 1974. Biophys. Res. Cornmiin. 5 I.
243
690 14.
15. 16.
VAN
-
De Goeij. A . F . P . L I . . Van S t r a a l e n , R.J.C. and Van Steveninck. J.. C l i n . Cltim. hcto. : 4 8 5 . 1976. Spikes. J . D . , Anti. N.Y. Acad. S c i . 264 : 496. 1975. Krinsky. N.I., Trciids i t i Biuclieiu. Sci. : 35. 1977.
Nmdived: ,h~ 1 1 , 1977; &mq.~t.e~i: J u l y 25, 1:)77.
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STEVENINCK ET AL.
679-690 (1977)
BINDING OF PROTOPORPIIYRIN TO tlEMOGLOBIN IN RED BLOOD
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CELLS OF PATIENTS WITH ERYTHROPOIETIC PROTOPORPHYRIA
J. van Steveninck, T.H.A.R.Dubbelmnn, A.F.P.M. de Coeij and L.N. Went Sylvius Laboratories Laboratory for Medical Chemistry and Department of Human Genetics Wassenaarseweg 72 Leiden, The Netherlands
Abstract Virtually all protoporphyrin in erythrocytes of patients vith erythropoietic protoporphyria is bound to hemoglobin. The maximum of the fluorescence excitation spectrum of this protoporpliyrin-hemoglobin complex shifted, with increasing concentration, from 405 nm to 389 nm. A similar shirt was observed wlien titrating a solution of free protoporphyrin with hemop;lobin. The Soret maximum of free protoporphyrin itself. on the other hand, was not concentrationdependent. These observations indicate that spectrofluorometric measurements do not allow conclusions coticerning the mode of protoporphyrin binding to hemoglobin. Experiments on protoporphyrin exchange between the hemoglobins A , F and S reinforced the previously drawn conclusion that protoporphyrin is bound to hemoglobin at the heme-binding sites.
Introduction The protoporpliyrin concentration in red blood cells of patients with erythropoietic protoporphyria (EPP) is invariably increased. This
679 Copyriplit 0 1977 hy Marcel I k k k c r . lnc A l l Rielits Rrrctvrd Nrilhcr I h i q work nor any p:trl may hc reproduced or Iransniillcd in any h r r n o r hy any nicafts. rlrrtronic or nicchanical. inclucltny . hy any infnrninlitin slorafic arid rrltievai Sy5lCni. photocopying. microfilming. and 1 ~ ~ 0 r d t t 1 por without permission in writins front the puhlirlter.
680
VAN STEVENINCK
ET AL.
is caused by a genetically determined decrease of heme synthetase activity (1-4) in the final stage of erythroid.development ( 1 ) . The accumulated protoporpliyrin is bound to hemoglobin inside the cells (5.6).
We concluded. based on isoelectric focusing and
protoporphyrin-hemoglobin binding experiments, that protoporpliyrin
was bound at the heme-binding sites (5).
Spectrofluorometric mea-
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surements, on the other hand, seemed to indicate a protoporpliyrin binding at sites other than the heme-binding sites (6).
In view
of this apparent contradiction, this problem was reinvestigated. Measurements of absorption spectra of hemoglobins and of fluorescence excitation spectra of protoporphyrin and of hemolysates of red blood cells of EPP patients showed that the spectral data should be explained in a way different from that proposed by Lamola et al. (6). The interpretation of the spectral data presented in this paper does not contradict a binding of protoporphyrin at the heme-binding sites of hemoglobin. The protoporphyrin-lirmoglobin binding experiments were extended with protoporpliyriii exchange measurements between adult hemoglobin A, fetal hemoglobin and sickle cell hemoglobin S. These experiments corroborated the conclusion that protoporphyrin binds at the heme-binding sites of hemoglobin. Methods Freshly drawn heparinized human blood was centrifuged and uastied with buffered isotonic NaCl solution shortly after collection.
Hemolysis was evoked by mixing one volume of washed red
blood cells with two volwiies of distilled water.
The soluble cell
fraction was obtained by centrifugation at 48,000 X g during 30 min at 4OC.
Hemoglobin concentrations were measured according
to Crosby et al. (7).
Conversion of hemoglobin to hemiglobin
(methemoglobin) was accomplished uith K3Fe(CN)6.
as described by
Bunn and Jandl ( 8 ) . Electrophoretic separation of hemoglobins was done in starch gels, as described previously (5).
Protoporphyrin was extracted
BINDING OF I'ROTOPORPIIYRIN
TO ILEMOCLOBIN
681
from the gels according to Schwartz et al. ( 9 ) aEter homogenizing the gel in a Potter apparatus.
The protoporphyrin concentration
was measured fluorometrically. Light absorption spectra were measured on a Beckmann D . B . spectrophotometer.
Fluorescence excitation spectra were recorded
on a Aminco-Bowman spectrophotofluorometer.
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Results The fluorescence excitation spectrum of the soluble cell fraction of EPP red blood cells at two different dilutions is shown in Fig. I.
Apparently the Soret maximum is concentration-
dependent: with increasing concentration the maximum shifted to a lower wavelength.
Tlie maximum at 315 nm, on the other hand, did
not show a concentration-dependent shift.
The relationship be-
tween concentration and Soret maximtim is shown in Fig. 2. The fluorescence excitation spectrum of pure protoporphyrin dissolved in buffered isotonic NaCl solution exhibits maxima at
405 and 315 nm.
The wavelength of these maxima appeared to be
independent of the protoporphyrin concentration.
If, Iiowever,
increasing amounts of hemoglobin were added to the protoporphyrin solution, a gradual shift of the Soret maximum to lower wavelengths was observed again.
At lov concentrations hemiglobin
provoked a similar shift of the Soret maximum.
With increasing
concentrations of hemiglobin this shift to lower vavelcngtlis continued, whereas concomitantly a second maxinnim appeared at about 420 nm (Fig. 3).
These phenomena can be explained from the fluorescence excitation spectrum of protoporphyrin and the absorption spectra of hemoglobin and hemiglobin.
As shovn in Fig.
4, the Soret band
of pure protoporphyrin, dissolved in buffered isotonic NaC1, extends from 340 to 450 nm, vith a maximum at 405 nm.
The absorp-
tion spectra o f hemoglobin and hemiglobin cover this excitation spectrum to a considerable degree. but not completely. hemoglobin absorbs strongly.
At 405
nm
At 390 nm the fluorescence excita-
VAN STEVENINCK ET AL.
682
0,
u 100 C at u
:80 In
Hemoglobin Downloaded from informahealthcare.com by University of Otago on 12/26/14 For personal use only.
3
60
40
20
I
I
300
3 50
I
I
LOO 150 excitation wavelength, nm
FICUKE I
Fluorescence excitation spectrum (for fluorescence at 6 2 5 nm) of the soluble cell fraction of EPP red blood cells diluted I :20,000 (-1 and I : 2,000 (----) respectively. Fluorescence is expressed i n arbitrary units.
tion efficiency is about 86% of that at 405 nm.
The absorbance of
hemoglobin at 390 nm, however, is only 45% of its absorbance at
405 nm.
Therefore, vith increasing hemoglobin concentrations,
fluorescence excitation at 405
NU
will be strongly quenched,
whereas fluorescence excitation at 390
NIL
will be much less
quenched. Thus, at sufficiently high hemoglobin concentrations, fluorescence excitation will be more effective at 390 nm than at
BINDING OF FROTOPORPlIYRIN TO HEMOGLOBIN
683
E
E’
.-
X
Hemoglobin Downloaded from informahealthcare.com by University of Otago on 12/26/14 For personal use only.
402
394
386t
, \
40
*
,
,
,
80
120
160
200
5
dilution factor x10 FIGURE 2
Relationship between the Soret maximum and the concentration of the liemolysate of EPP erythrocytes.
,405 nm.
This inner filter effect of hemoglobin explains the
gradual shift of the protoporpliyrin fluorescence excitation maximum to lower wavelengths witti increasing hemoglobin concentrations (Figs. 1 and 2). The appearance of a second peak at 420 nm after addition of hemiglobin can be similarly explained.
The absorbance of hrmi-
globin drops much faster between 4 0 5 and 4 2 5 nm than the absorbance of hemoglobin (Fig. 4).
The fluorescence excitation efficiency at
420 nm is about 6OX of the efficiency at 405 nm, whereas the ab-
VAN STEVENINCK ET AL.
684 Q,
C
100
0,
u
ln
E0
= 80 Hemoglobin Downloaded from informahealthcare.com by University of Otago on 12/26/14 For personal use only.
3
60
LO
20
1
I
350
300
I
I
LOO L50 excitation wavelength. nm
FlCURF, 3
Fluorescence excitation spectrum of 1.6 pH protoporphyrin in isotonic NaC1, pll 7.4. control; : 4 ubl hemiglobin added; : 8 VM hemiglobin added; -*-*: 16 uM hemiglobin added.
..--
- .-
----
sorbance of hemiglobin at 420 nm is only 302 of that a t 405 MI. Thus, using similar lines of reasoning, one could anticipate the appearance of a new peak around 420 nm at increasing hemiglobin concentrations. This interpretation of the results was confirmed by measurements of the fluorescence excitation spectrum of protoporphyrin. while a second cuvet containing varying concentrations of hemoglobin or hemiglobin was placed in the pathway of the exciting
BINDING OF PROTOPORPHYRIN TO IIEMOGLOBIN
$100
685
-
C 0
e0
In D
-
0
80
-
60
-
40
-
20
-
0)
u
C
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Q,
0 ul
o,
L
0 3
.c
L
I
1
I
FIGURE 4 Absorption spectra of hemoglobin (----) nnd liemiglobin ( . * . * ) fluorescence excitation spectrum of protoporpliyrin (-).
light beam.
and
Exactly the same shifts of the fluorescence excitation
maximum were observed, even though the protoporphyrin and the hcmoglobin were spatially separated. I n further experiments stroma-free hemolysate of EPP red blood
cells was mixed with hemoglobin F and hemoglobin S respectively. The mixtures were incubated during 3 hours at 37OC. Subsequent starch gel electrophoresis yielded the results schematically The parts of the gel vhere the different
depicted in Fig. 5, a-c.
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686
3
VAN
STEVENTNCK ET AL.
I I
FIGURE 5 S t a r c h g e l e l e c t r o p l i o r e s i s of liemolysate of EPP r e d c e l l s i n c u b a t e d a l o n e ( a and d ) , v i t h hemoglobin S (b and e ) and w i t h henloglobin F (c and f ) . I n a - c t h e i n c u b a t i o n s vere c a r r i e d o u t v i t h o u t pretreatment. In d f t h e hemoglobins vere c o n v e r t e d i n t o hemiglobins p r i o r t o incubation.
-
hemoglobin f r a c t i o n s were o b s e r v e d were c u t o u t and a s s a y e d f o r protoporphyrin.
No p r o t o p o r p h y r i n exchange o c c u r r e d : a l l p r o t o -
p o r p h y r i n was r e c o v e r e d a t t h e p o s i t i o n of hemoglobin A , d e r i v e d from t h e EPP r e d blood c e l l s .
I f t h e hemoglobins v e r e c o n v e r t e d t o
hemiglobin p r i o r to mixing and i n c u b a t i o n . t h e e l e c t r o p h o r e s i s p a t t e r n shovn i n F i g . 5 , d - f . was o b t a i n e d .
Under t h e s e citcum-
s t a n c e s p r o t o p o r p h y r i n was exchanged between t h e hemiglobin A of t h e EPP p a t i e n t and hemiglobins F atid S r e s p e c t i v e l y .
The amount
6R7
B I N D I N G OF PROTOPORF'HYRLN TO IIEFIOCLOBIFI
o f p r o t o p o r p l i y r i n found iii t h e d i f f e r e n t IiemiRlohin f r a c t i o n s was p r o p o r t i o n a l t o t h e r e l a t i v e amount of t h e + e F r a c t i o n s . i n d i c a t i n g a 1002 exchanRe a c c o r d i n g t o t h e c a l c u l a t i o n s Riven
hy Bcinn and
J a n d l (8). Discussion
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P r o t o p o r p h y r i n , a c c u m u l a t e d i n e r y t h r o c y t e s of EPP p a t i e n t s .
is hound t o hemoglobin ( 5 . 6 ) .
Lamola e t a l . ( 6 ) found a f l i i o r e s -
c e n r e e x c i t a t i o n maximum o f l i e m o l y s a t e s d e r i v r d from EPF r e d b l o o d
c e l l s a t 397 nm.
P r o t o p o r p h y r i n i n c u b a t e d w i t h henloRlohin A had a
maximrim a t ttie same wavelenRtli. w h e r e a s p r n t o p o r p h y r i n i n c u b a t e d w i t h g l o h i n showed a maximum a t 4 0 3 nm.
T h e s e d a t a were i n t e r -
p r e t e d as i n d i c a t i n g a s t r i i c t c i r a l d i f f e r e n c e hetween t h e Iieninlysate
of EPP r e d b l o o d c e l l s and the. protoporpliyrin-liemoglohin A complex on tlie o n e hand and t h e p r o t o p o r p h y r i n - R l o h i n Since i n t h e protoporphyrin-glohin
romplex on ttie o k h e r .
complex tlie p r o t o p o r p h y r i n
b i n d i n g occurs a t t h e heme-hinding s i t w (10- 1 2 ) .
i t waq s u g R e s t e d
t h a t b o t h i n t h e protoporphyrin-hemoRLobin A complex and i n t h e t i e m o l y s a t e o f EPP r e d b l o o d c e l l s tlie h i n d i n 8 r i r r r i r r r d a t n t l i e r
sites.
T h i s i n t e r p r e t a t i o n i s r e f u t e d hy t h e r e s u l t s p r e s e n t e d i n
t h i s paper.
As h a s been shown. t h e f l u o r e s c e n c e e x c i t a t i o n maxi-
mum o f b o t h t h e h e n m l y s a t e o f EPP r e d blood c e l l s and t l i r p r o t o porpliyrin-liemoy,lobin
A complex i s c o n c r n t r a t i n n - d e p e n d e n t .
t h e i n n e r f i l t e r e f f e c t of hemoglobin. measured by Lamola e t a l . ( 6 ) a t
R
due t o
The maxinium a t 397 nm was
d i l u t i o n of ahoiit I : 2.000.
T h i s a g r e e s w i t h t h e r e s u l t s p r e s e n t e d i n FiR. 2 .
I t cnn b e i n f e r -
r e d t h a t t h e s e s p e c t r o f l u o r o n i e t r i c measurements do n o t a l l o w conc l u s i o n s c o n c e r n i n g tlie mode o f p r o t o p o r p h y r i n b i n d i n g to hcmoglobin. I n a p r e v i o u s p a p e r i t was c o n c l u d e d t h a t i n El'P
rcd blood
c e l l s tlie p r o t o p o r p h y r i n i s bound t o liemoglohin a t t h e heme-bindin8 sites (5).
T h i s was b a s e d o n t h e f o l l o w i n g o b s e r v a t i o n s .
notti
w i t h i s o e l e c t r i c f o c u s i n g and w i t h s t a r c h g e l e l e c t r o p h o r e s i s of hemolyzed EPP e r y t h r o c y t e s t h e p r o t o p n r p h y r i n was r e c o v e r e d a t t h e
VAN STEVENLNCK E T AI..
688
p o s i t i o n of heiiwglobin. M i x t b r e s of p r o t o p o r p h y r i n and hemoglobin gave q u i t e d i f f e r e n t r e s u l t s . With i s o e l e c t r i c f o c u s i n g t h e prot o p o r p h y r i n moved i n t o tlie anode s o l u t i o n and w i t h s t a r c h g e l e l e c t r o p h o r e s i s i t s t r e a k e d froin t h e a p p l i c a t i o n l i n e i n tlie d i r e c t i o n of tlte anode. These r e s t i l t s r e v e a l e d a n e s s e n t i a l d i f f e r e n c e between ttie p r o c o p ( ~ r p l i y r i i i - l i e i i i ~ g l o b i icomplex i p r e s e n t i n EPP red
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blood c e l l s and tlie coinl1Irx formed by i n c u b a t i o n of p r o t o p o r p h y r i n with normal Iirinoglobiii. 'llie e x i s t e n c e of t h e l a t t e r complex can be demonstrated by g e l f i l t r a t i o n on Sephadex G 100. w i t t i hemoglobin and p r o t o p o r p l i y r i n e i t i t i n g i n tlie same f r a c t i o n w i t h an a p p a r e n t m o l e c u l a r weight o f a b o u t , 70,000 d a l t o n s . T h i s complex i s d i s r u p t e d , Iiowever, by e l e c t r i c a l f o r c e s b o t h d u r i n g i s o e l e c t r i c f o c u s i n g and s t a r c h e l e c t r o p h o r e s i s , wliereas tlie complex, p r e s e n t i n EI'P r e d blood c e l l s is s t a b l e under Lliese c i r c u m s t a n c e s . A f t e r i n c u b a t i o n o f p r o t o p o r p h y r i n w i t h liemiglobin, however, a protoporpliyriii-liemiglobin complex i s fornied w i t h ~ l i rsame c l i a r a c t e r i s t i c s a s t h e p r o t o p o r p h y r i n hemiglobin coniplex d e r i v e d froiii EPP e r y t h r o c y t e s , b o t h w i t t i r e f e r e n c e t o i s o e l e c t r i c f o c u s i n g and t o s t a r c h g e l e l e c t r o p h o r e s i s (5). S i n c e t h e f e r r i h e n i e grotip is mcich l e s s f i r m l y bound t o g l o b i n tlian t h e normal heme group ( 8 . 1 3 ) .
these r e s u l t s indicate that a
spontaneous replacement of Iiemt! by p r o t o p o r p h y r i n does not t a k e p l a c e . whereas p r o t o p o r l ) l i y r i n - f ~ r r i h e m e exchange can o c c u r r e a d i l y . The roncliisioii t h a t i n EPP red blood c e l l s p r o t o p o r p h y r i n is bowid t o hcinoglobin a t t h e heme-binding s i t e s i s r e i n f o r c e d b y t h e e x p e r i m e n t a l r e s u l t s o u t l i n e d i n F i g . 5. A f t e r e l e c t r o p l i o r e s i s of a liemolysate of EPP e r y t h r o c y t e s L l i e p r o t o p o r p l i y r i n was r e c o v e r e d a t ttie p o s i t ' i o n of Iienioglobin A . No exchange of p r o t o p o r p t i y r i n between tlie hemoglobin A aiid hemoglobin F o r S took p l a c e d u r i u g p r e i n c u b a t i o n . A f t e r coiiversion t o h e m i g l o b i n , however, 100%exchange of p r o t o p o r p h y r i n occur.rcd. b o t h i n t h e hemiglobin Ahemiglobin F and i n tlie hciaiglobin A
-
hemiglobin S m i x t u r e . The
most obvious i i i t e r p r e L d t i o n a g a i n is t h a t protoporpliyritl is bound a~ heme-binding
s i t e s of tlte Ireinoglolin m o l e c u l e s . 'The experimen-
t a l r e s u l t s can t h e n he r a t i o n a l i z e d on t h e b a s i s of n o exchange
between p r o t o p o r p l i y r i n and Lhe s t r o n g l y bound heiiie group and a
BINDING O F PROTOPORPIIYRIN TO HMOG1,OBJN
689
rattier easy exctianre hetween protoporpltyrin arid ilie l o o s e l y hotlnd
f err i heme grotip. W l t m irradiated witti visihle light red I>lood rrlls from patients
with EPP readily 1tc.molyze. a s a consequence o f prntnporpltyrin-iridtlced pltotodyriamic memhrnnt- danmpe ( 1 4 ) . The descrihcd binding of protoporpttyrin to hemoglohin is not
iii
contradiction wit11 this observation.
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The photodynamic process is mediated via the formation of singlet oxygen (15). A s pointed out b y Krinsky (16) this singlet oxygen can dirfose over relatively great distances in biological systems. before being qriencltetl.
Acknowledgement Ttie authors are much indebted to Karnti Cltristianst- f o r her ski1 ful technical assistance. References De Coeij, A.F.P.M., Cliristianse, K. and Van Steveninck. J . . Europ. J . Clin. Invest.. 5: 397, 1975. 2. Bloomer, J . R . , Bonkovsky, A.L., Ebert. F.S. and Malioney. M.J., Lancet, 226, 1976. 3. Bottomley. S.S., Tanaka. If. and Everett. M . A . . J . Lab. Clin. Med., 2 : 126, 1975. 4. Bonkovsky, H.L., Bloomer. J.R., Ebert, P.S. and Malioney, M.J.. J . Clin. Invest.. 5 G : 1139, 1975. Van-Steveninck, J . arid Went, L.N.. Clin. 5. De Goeij, A.F.P.M., Chim. Acta, 6 3 : 355. 1975. 6 . Lamola, A . A . , P i z e l l i , S., Poll-Fitzpatrick, F 1 . U . . Yamnne. T. and Ilarbcr, L.C.. .I. Clin. Invest., 56: 1528. 1975. 7. Croshy. W . H . , Munn. J. I. and Furth, F.W., U.S. Armed Forces Med. J . , 5 : 6 9 3 , 1954. : 4 6 5 . 1968. 8. Biinn, H.F. a n z Jandl, J . H . , J . Biol. C l i r m . , Bossenmaier. I. and Dinsmore, H., 9. Schwartz, S., Berg, M.11.. in: Methods of Biocliemical Analysis, vol. 8. edited by D. GLick, page 221. Interscience Publishers Inc.. New York. 1960. 10. Leonard, J . J . , Yonetani, T. and Callis, J . U . , Biocliemistry. 13: 1460, 1974. I t . RossFFanelli. h . . Antonini. E. and Caputo, A . , Biochim. Biopliys. Acta 35 : 93, 1959. 12. Treffry, A . and AiGworth. S., Biochem. J. 137 : 319. 1974. 13. Schulman. H.M., Martinez-Medellin, J . and Sidloi. R . . Biochem. 5 : 220, 1974. Biophys. Res. Cornmiin. 5 I.
243
690 14.
15. 16.
VAN
-
De Goeij. A . F . P . L I . . Van S t r a a l e n , R.J.C. and Van Steveninck. J.. C l i n . Cltim. hcto. : 4 8 5 . 1976. Spikes. J . D . , Anti. N.Y. Acad. S c i . 264 : 496. 1975. Krinsky. N.I., Trciids i t i Biuclieiu. Sci. : 35. 1977.
Nmdived: ,h~ 1 1 , 1977; &mq.~t.e~i: J u l y 25, 1:)77.
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STEVENINCK ET AL.
