99
Biochimica et Biophysica Acta,
499 (1977) 99--110 © Elsevier/North-Holland Biomedical Press
BBA 28293
GLUCONEOGENESIS IN RABBIT LIVER II. GLUCONEOGENESIS AND ITS ENHANCEMENT BY GLUCAGON, EPINEPHRINE AND CYCLIC AMP *
CHARLES
A. HUIBREGTSE
**, GERALD
A. R U F O , J r. a n d P A U L D. R A Y * * *
The Guy and Bertha Ireland Research Laboratory, Department of Biochemistry, University of North Dakata School of Medicine, Grand Forks, N.D. 58202 (U.S.A.) (Received January 12th, 1977)
Summary 1. Gluconeogenesis from various substrates has been demonstrated in isolated rabbit liver. Rates of gluconeogenesis (in/~mol per min/g liver) for various substrates are as follows: D-fructose, 0.95; dihydroxyacetone, 0.60; L-lactate, 0.52; glycerol, 0.34. L-alanine does not substantially enhance gluconeogenesis. 2. Gluconeogenesis from L-lactate and dihydroxyacetone is stimulated approx. 1.7--1.8 fold by 10 -s M glucagon, 10 -4 M epinephrine and 10 -4 M cyclic AMP. Gluconeogenesis from D-fructose is stimulated only 1.3-fold by cyclic AMP. 3. Plots of hepatic metabolite concentrations, before and after addition of effectors to livers given L-lactate or dihydroxyacetone show highly significant increases (P < 0.02) in the concentrations of fructose 6-phosphate and glucose 6-phosphate after addition of effectors. Data suggest that glucagon, epinephrine and cyclic AMP exert a major positive influence on the interconversion of fructose 1,6-diphosphate and fructose 6-phosphate; conversely, data provide no evidence for a significant influence of these effectors on the conversion of L-lactate to phosphoenolpyruvate. 4. Quinolinic acid is ineffective as an inhibitor of gluconeogenesis from L-lactate in fasted rabbit livers; aminooxyacetate at various concentrations inhibits gluconeogenesis from L-lactate by 50--70%, suggesting that cytosolic phosphoenolpyruvate carboxykinase compared to the mitochondrial carboxykinase is
* Part of the data in this paper waS t a k e n from a dissertation submitted by C.A.H. t o the Graduate School of the University of North Dakota. A p r e l i m i n a r y re port haS been presented before the American Society of Biological Chemists [1]. ** Current address: St. Louis Univ. Sch. of Medicine, Dept. of Biochemistry, 1402 S. Grand Blvd., St. Louis, Mo. 63104. *** To w h o m rep rin t requests should be sent.
100 of at least equal importance for synthesis of phosphoenolpyruvate en route to glucose.
Introduction
Gluconeogenesis has been under intensive study, especially during the last decade, but in most cases the rat has been the experimental animal. Investigators have shown that the isolated rat liver can convert L-alanine, pyruvate, L-lactate, glycerol, dihydroxyacetone, D-glyceraldehyde and D-fructose to D-glucose [2--6 ]. Regulatory sites between pyruvate and phosphoenolpyruvate [5--11] and between fructose 1,6
Biochimica et Biophysica Acta,
499 (1977) 99--110 © Elsevier/North-Holland Biomedical Press
BBA 28293
GLUCONEOGENESIS IN RABBIT LIVER II. GLUCONEOGENESIS AND ITS ENHANCEMENT BY GLUCAGON, EPINEPHRINE AND CYCLIC AMP *
CHARLES
A. HUIBREGTSE
**, GERALD
A. R U F O , J r. a n d P A U L D. R A Y * * *
The Guy and Bertha Ireland Research Laboratory, Department of Biochemistry, University of North Dakata School of Medicine, Grand Forks, N.D. 58202 (U.S.A.) (Received January 12th, 1977)
Summary 1. Gluconeogenesis from various substrates has been demonstrated in isolated rabbit liver. Rates of gluconeogenesis (in/~mol per min/g liver) for various substrates are as follows: D-fructose, 0.95; dihydroxyacetone, 0.60; L-lactate, 0.52; glycerol, 0.34. L-alanine does not substantially enhance gluconeogenesis. 2. Gluconeogenesis from L-lactate and dihydroxyacetone is stimulated approx. 1.7--1.8 fold by 10 -s M glucagon, 10 -4 M epinephrine and 10 -4 M cyclic AMP. Gluconeogenesis from D-fructose is stimulated only 1.3-fold by cyclic AMP. 3. Plots of hepatic metabolite concentrations, before and after addition of effectors to livers given L-lactate or dihydroxyacetone show highly significant increases (P < 0.02) in the concentrations of fructose 6-phosphate and glucose 6-phosphate after addition of effectors. Data suggest that glucagon, epinephrine and cyclic AMP exert a major positive influence on the interconversion of fructose 1,6-diphosphate and fructose 6-phosphate; conversely, data provide no evidence for a significant influence of these effectors on the conversion of L-lactate to phosphoenolpyruvate. 4. Quinolinic acid is ineffective as an inhibitor of gluconeogenesis from L-lactate in fasted rabbit livers; aminooxyacetate at various concentrations inhibits gluconeogenesis from L-lactate by 50--70%, suggesting that cytosolic phosphoenolpyruvate carboxykinase compared to the mitochondrial carboxykinase is
* Part of the data in this paper waS t a k e n from a dissertation submitted by C.A.H. t o the Graduate School of the University of North Dakota. A p r e l i m i n a r y re port haS been presented before the American Society of Biological Chemists [1]. ** Current address: St. Louis Univ. Sch. of Medicine, Dept. of Biochemistry, 1402 S. Grand Blvd., St. Louis, Mo. 63104. *** To w h o m rep rin t requests should be sent.
100 of at least equal importance for synthesis of phosphoenolpyruvate en route to glucose.
Introduction
Gluconeogenesis has been under intensive study, especially during the last decade, but in most cases the rat has been the experimental animal. Investigators have shown that the isolated rat liver can convert L-alanine, pyruvate, L-lactate, glycerol, dihydroxyacetone, D-glyceraldehyde and D-fructose to D-glucose [2--6 ]. Regulatory sites between pyruvate and phosphoenolpyruvate [5--11] and between fructose 1,6
