The 11β hydroxysteroid dehydrogenase 2 exists as an inactive dimer

Abstract The 11β-hydroxysteroid dehydrogenase types 1 and 2 enzymes (11β-HSD1 and 11β-HSD2), modulate glucocorticoid occupation of the mineralocorticoid and glucocorticoid receptors by interconverting corticosterone and cortisol to the inactive metabolites 11-dehydrocorticosterone and cortisone within the target cells. The NAD + -dependent 11-HSD 2 in the kidney inactivates corticosterone and cortisol, allowing aldosterone, which is not metabolized, access to the receptor. Studies of the kinetics of 11-HSD 2 activity in the rat kidney have produced inconsistent results. Western blots done in the absence of the reducing agent β-mercaptoethanol showed two bands with approximate MW of 40 and 80 kDa. When β-mercaptoethanol was used, only the 40 kDa was detected, indicating that under non-denaturing conditions a significant proportion of the 11β-HSD 2 exists as a dimer. NAD + -dependent conversion of 3 H-corticosterone by 20 μg of microsomal protein increased approximately 10 fold with the addition of 5 mM DTT concentration. NADP + -dependent activity with 20 μg of microsomal protein was very low and did not change significantly when using DTT. In the presence of DTT, the predominant 11-HSD activity in the rat kidney is NAD + -dependent with a K m of 15.1 nM, similar to that of the cloned and expressed enzyme. These data suggest that dimerization and subsequent enzyme inactivation occur when protocols promoting oxidation of this protein are used.