Abstract
When microsomes were prepared in 2-mercaptoethanol V max for 17β -hydroxysteroid oxidoreductase(17β -HSD) was greater, the K m for NAD+ was greater and the K m for testosterone lower than in its absence. During storage at 4δ V max increased in the presence of 2-mercaptoethanol and decreased in its absence; K m 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 17β -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 17β -HSD reflect a conformational flexibility at the active site and are not due to extensive changes in the structure of the microsomes. 17β -HSD exposed to 2-mercaptoethanol was subject to substrate inhibition by testosterone, a type of inhibition not previously reported for this enzyme.
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