title: Effects of 2-mercaptoethanol and aging in vitro on 17beta-hydroxysteroid oxidoreductase of guinea pig liver microsomes.
abstract: When microsomes were prepared in 2-mercaptoethanol Vmax for 17beta-hydroxysteroid oxidoreductase (17beta-HSD) was greater, the Km for NAD+ was greater and the Km for testosterone lower than in its absence. During storage at 4 degrees Vmax increased in the presence of 2-mercaptoethanol and decreased in its absence; Km values for testosterone and NAD+ increased during storage in both cases. The presence or absence of 2-mercaptoethanol did not affect the extent or time-course of inactivation of 17beta-HSD by trypsin or phospholipase A. Furthermore, no differences were detected in sedimentation properties on sucrose density gradients suggesting that the differences and changes in the kinetic behavior of 17beta-HSD reflect a conformational flexibility at the active site and are not due to extensive changes in the structure of the microsomes. 17beta-HSD exposed to 2-mercaptoethanol was subject to substrate inhibition by testosterone, a type of inhibition not previously reported for this enzyme.
mesh_terms: D015067:17-Hydroxysteroid Dehydrogenases / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D002499:Centrifugation, Density Gradient; D006168:Guinea Pigs; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008623:Mercaptoethanol / Q000494:pharmacology*; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D009243:NAD / Q000378:metabolism; D010740:Phospholipases / Q000494:pharmacology; D013997:Time Factors; D014357:Trypsin / Q000494:pharmacology
chemical_list: D000596:Amino Acids; D009243:NAD; D008623:Mercaptoethanol; D015067:17-Hydroxysteroid Dehydrogenases; D010740:Phospholipases; D014357:Trypsin