EFFECT OF STEROID STRUCTURE ON INHIBITION OF LANOSTEROL DEMETHYLATION BY STEROID HORMONES

Steroid hormones inhibit the oxidative demethylation of lanosterol that is catalyzed by testicular microsomal enzymes. The apparent inhibition constant, Ki′, for more than 40 steroids varies 100-fold from 0.05 to 5 mM. Thus, considerable structural specificity is demonstrated. However, relatively high concentrations of all steroids are required for inhibition and testosterone, a major testicular steroid metabolite, is only a moderately active inhibitor (Ki′, 0.04 mM). Thus, conclusions regarding the physiological significance of this apparent end product inhibition should be tempered until the process is examined by other experimental approaches. © 1968.