title: Inactivation of microsomal 17 beta-hydroxysteroid dehydrogenase by phospholipase C: rates of phospholipid hydrolysis and enzyme inactivation, and effects of phospholipids.
abstract: When guinea-pig liver microsomes were exposed to phospholipase C the rate of phospholipid hydrolysis exceeded the rate of decrease in 17 beta-hydroxysteriod dehydrogenase (17 beta-HSD) activity. The time-course of the decrease in 17 beta-HSD activity was biphasic. An initial more rapid decrease (30-50% of total) was associated with the major extent (85%) of phospholipid hydrolysis. Subsequently, a second, slower phase of 17 beta-HSD inactivation was observed. The addition of purified phospholipids did not reactivate 17 beta-HSD but did protect against the inactivation seen in the second phase. The diacyglycerides produced by phospholipase C action remained associated with the microsomes. It is proposed that the differences in the rates of 17 beta-HSD inactivation reflect variations in the distribution of a single form of 17 beta-HSD among differing membrane fractions rather than the existence of multiple enzyme forms. The stabilizing effects of phospholipids may be due to their ability to prevent changes in lipid-lipid, lipid-protein and protein-protein interactions resulting from diacylglyceride formation. Resuspended microsomal lipids (chloroform-methanol extracts) inactivated 17 beta-HSD suggestive of the presence of endogenous lipid modulators of enzymatic activity.
mesh_terms: D015067:17-Hydroxysteroid Dehydrogenases / Q000037:antagonists & inhibitors*; D000818:Animals; D002499:Centrifugation, Density Gradient; D006168:Guinea Pigs; D006868:Hydrolysis; D007700:Kinetics; D008862:Microsomes, Liver / Q000201:enzymology*; D010712:Phosphatidic Acids / Q000494:pharmacology; D010713:Phosphatidylcholines / Q000494:pharmacology; D010740:Phospholipases / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism*; D013997:Time Factors; D010738:Type C Phospholipases / Q000378:metabolism*
chemical_list: D010712:Phosphatidic Acids; D010713:Phosphatidylcholines; D010743:Phospholipids; D015067:17-Hydroxysteroid Dehydrogenases; D010740:Phospholipases; D010738:Type C Phospholipases