title: Control of placental 3 beta-hydroxy-delta 5-steroid dehydrogenase: partial characterization of an endogenous inhibitor and an endogenous activator.
abstract: Two substances which affect the activity and kinetic characteristics of 3 beta-hydroxy-delta 5-steroid dehydrogenase (delta 5-3 beta-HSD) have been recovered from homogenates of term human placenta by extraction with organic solvents after ethanol precipitation of protein. One of these substances, an inhibitor of the enzyme, is a non-polar unstable substance, which dialyzes through a cellulose nitrate membrane and which appears to be present in the tissue both in the free state and bound to either the enzyme or the microsomal membrane. It was not possible to produce a delta 5-3 beta-HSD preparation free of the inhibitor. The other substance is an activator, polar and stable with a molecular weight of less then 500, which increases both the apparent Km and the apparent V max of delta 5-3 beta-HSD. It is postulated that both substances play a part in control of placental progesterone synthesis.
mesh_terms: D015096:3-Hydroxysteroid Dehydrogenases / Q000037:antagonists & inhibitors*; D055598:Chemical Phenomena; D002621:Chemistry; D004789:Enzyme Activation; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008722:Methods; D010920:Placenta / Q000201:enzymology*; D011374:Progesterone / Q000096:biosynthesis
chemical_list: D011374:Progesterone; D015096:3-Hydroxysteroid Dehydrogenases