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Ornithine Decarboxylase in Cartilage: Occurrence and Regulation by Human Plasma in vitro P. D. CONROY, D. M. SIMMS, K. ASHTON* & M. J. O. FRANCIS Nuffield Dept. of Orthopaedic Surgery, Oxford University, Oxford OX3 7LD, England
Polyamines have been detected at up to millimolar concentrations in many animal tissues, there being generally a positive correlation with the growth rate of the tissue. The function of these high concentrations of intracellular polycations is unresolved, but may involve binding to acidic components of the cell such as nucleic acids and phospholipids [3]. Ornithine decarboxylase (ODC) E.C.4.1.1.17, is the first enzyme in the biosynthetic pathway forming polyamines in animal tissues. The activity of ODC is raised in a number of tissues following growth hormone administration [5]. Cartilage from young growing animals contains a high proportion of hypertrophic and proliferative cells and is also a main target tissue for growth hormone. Consequently we have investigated the levels of ODC in cartilage and established an in vitro system for studying the regulation of the enzyme in cartilage. ODC was assayed by monitoring release of 14CO2 from L-114C-ornithine upon incubation with tissue extract [4]. Units of ODC activity are presented as nmoles ornithine decarboxylated/30 min/g tissue (wet weight). Levels of ODC detected were 3--24 units (10--14-day-old chick embryo pelvic cartilage), 0.9--1.7 units (25-week human foetal costal cartilage), 5--19 units (4-week rabbit costal and articular cartilage) and 0.2--0.4 (4-week rat costal cartilage). These levels varied from 0.5 to 0.05 of those found in liver. No ODC was detected in bone. When compared on the basis of total soluble protein in the extract rather than tissue wet weight, chick embryo liver and pelvic cartilage contained 0.98 and 0.92 units of ODC respectively. Pelvic cartilage from 11 to 13-day-old chick embryos was incubated in vitro in Waymouth's medium 752/1 supplemented with 1.75mM serine, 3.50mM
*Smith and NephewFoundation Fellow
377 glutamine and 2 0 r a m Hepes buffer pH 7.4. The cartilage ODC activity was maintained at the in vivo level following a 17.5 h incubation at 37~ Incubation in 10% (v/v) human plasma or serum for a further 4 h raised the cartilage ODC levels to 237% of controls incubated without plasma. Plasma also stimulated 3sSO4 incorporation into the cartilage macromolecules [1] by 38% (P
Ornithine Decarboxylase in Cartilage: Occurrence and Regulation by Human Plasma in vitro P. D. CONROY, D. M. SIMMS, K. ASHTON* & M. J. O. FRANCIS Nuffield Dept. of Orthopaedic Surgery, Oxford University, Oxford OX3 7LD, England
Polyamines have been detected at up to millimolar concentrations in many animal tissues, there being generally a positive correlation with the growth rate of the tissue. The function of these high concentrations of intracellular polycations is unresolved, but may involve binding to acidic components of the cell such as nucleic acids and phospholipids [3]. Ornithine decarboxylase (ODC) E.C.4.1.1.17, is the first enzyme in the biosynthetic pathway forming polyamines in animal tissues. The activity of ODC is raised in a number of tissues following growth hormone administration [5]. Cartilage from young growing animals contains a high proportion of hypertrophic and proliferative cells and is also a main target tissue for growth hormone. Consequently we have investigated the levels of ODC in cartilage and established an in vitro system for studying the regulation of the enzyme in cartilage. ODC was assayed by monitoring release of 14CO2 from L-114C-ornithine upon incubation with tissue extract [4]. Units of ODC activity are presented as nmoles ornithine decarboxylated/30 min/g tissue (wet weight). Levels of ODC detected were 3--24 units (10--14-day-old chick embryo pelvic cartilage), 0.9--1.7 units (25-week human foetal costal cartilage), 5--19 units (4-week rabbit costal and articular cartilage) and 0.2--0.4 (4-week rat costal cartilage). These levels varied from 0.5 to 0.05 of those found in liver. No ODC was detected in bone. When compared on the basis of total soluble protein in the extract rather than tissue wet weight, chick embryo liver and pelvic cartilage contained 0.98 and 0.92 units of ODC respectively. Pelvic cartilage from 11 to 13-day-old chick embryos was incubated in vitro in Waymouth's medium 752/1 supplemented with 1.75mM serine, 3.50mM
*Smith and NephewFoundation Fellow
377 glutamine and 2 0 r a m Hepes buffer pH 7.4. The cartilage ODC activity was maintained at the in vivo level following a 17.5 h incubation at 37~ Incubation in 10% (v/v) human plasma or serum for a further 4 h raised the cartilage ODC levels to 237% of controls incubated without plasma. Plasma also stimulated 3sSO4 incorporation into the cartilage macromolecules [1] by 38% (P
