Evidence for independent 11-oxidase and 11-reductase activities of 11 beta-hydroxysteroid dehydrogenase: enzyme latency, phase transitions, and lipid requirements.
Experimental modification of the membrane structure of rat liver microsomes affected the behavior of the 11-oxidase and 11-reductase components of 11 beta-hydroxysteroid dehydrogenase in different ways. 1) The latency of 11-oxidase was released by detergents, phospholipases, or elevated temperature; 11-reductase activity was not increased by these manipulations. 2) 11-Reductase was rapidly inactivated at 25 C and 37 C; 11-oxidase was stable at these temperatures. 3) Arrhenius plots of microsome bound 11-reductase between 5 C and 40 C showed discontinuity at 23 C. Activation energies above and below the critical temperature were 2 kcal and 16 kcal, respectively. Solubilized 11-reductase showed no discontinuity [activation energy (Ea) = 15 kcal]. Ea for 11-oxidase was 15 kcal at all temperatures for membrane bound or solubilized enzyme, with no discontinuities. 4) Phospholipases A2 and C rapidly inactivated 11-reductase. Triton DF-18 regenerated 50% of the reductase activity of phospholipase C-treated microsomes, but had no effect on phospholipase A2-treated microsomes. Phospholipases increased 11-oxidase activity. The independent behavior of corticosteroid 11-oxidase and 11-reductase are consistent with the properties of closely associated, independent enzymes.
D042842:11-beta-Hydroxysteroid Dehydrogenases; D000818:Animals; D006913:Hydroxysteroid Dehydrogenases / Q000378:metabolism*; D007700:Kinetics; D050356:Lipid Metabolism; D008297:Male; D008433:Mathematics; D008854:Microscopy, Electron; D008862:Microsomes, Liver / Q000201:enzymology / Q000648:ultrastructure; D010741:Phospholipases A / Q000378:metabolism; D054467:Phospholipases A2; D051381:Rats; D011919:Rats, Inbred Strains; D013696:Temperature; D010738:Type C Phospholipases / Q000378:metabolism
D006913:Hydroxysteroid Dehydrogenases; D042842:11-beta-Hydroxysteroid Dehydrogenases; D010741:Phospholipases A; D054467:Phospholipases A2; D010738:Type C Phospholipases