title: Rat liver 3-oxo-5 alpha-steroid delta 4-dehydrogenase. Modulation of enzyme activity by changes in phosphorylation state.
abstract: 3-Oxo-5 alpha-steroid: NAD+ delta 4-oxidoreductase ("NADH-5 alpha-reductase", EC 1.3.1.?) is rapidly inactivated in the presence of 17 beta-hydroxy-4-androsten-3-one (testosterone). This activation is prevented by increasing the phosphate concentration. When the enzyme assay is carried out in Tris-HCl, only a small activity (1.7 nmol X min-1 X mg-1) is observed which may be further decreased by addition of phosphatases. Addition of the phosphatase inhibitor dextran sulphate or ATP, Mg++ and c-AMP results in a significant increase of activity (228% and 273%, respectively) compared with the Tris-HCl control. Glycerol 2-phosphate and glycerol 3-phosphate have a stabilizing effect on 3-oxo-5 alpha-steroid: NAD+ delta 4-oxidoreductase by decreasing the Km towards the substrate testosterone from 1.2 X 10(-5) mol/l to 3.3 X 10(-6) mol/l. V remains unchanged. Half maximal velocity (testosterone reduction) is achieved with 20 mumol/l glycerol 2-phosphate and glycerol 3-phosphate. Addition of c-AMP dependent protein kinase (EC 2.7.1.37) to a microsomal preparation pretreated with alkaline phosphatase (EC 3.1.3.1) results in a significant increase of 3-oxo-5 alpha-steroid: NAD+ delta 4-oxidoreductase activity compared with the control.
mesh_terms: D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase / Q000378:metabolism*; D000818:Animals; D004789:Enzyme Activation; D005260:Female; D005994:Glycerophosphates / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008862:Microsomes, Liver / Q000201:enzymology; D010088:Oxidoreductases / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013739:Testosterone / Q000378:metabolism
chemical_list: D005994:Glycerophosphates; D013739:Testosterone; D010088:Oxidoreductases; D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase; D011494:Protein Kinases