REGULATION OF RAT TESTIS STEROID SULFATASE . A KINETIC STUDY

A variety of unconjugated steroids were found to inhibit the in vitro cleavage of dehydroepiandrosterone sulfate by rat testis tissue. The glucosiduronates of cortisol and cortisone had virtually noeffect on the cleavage of dehydroepiandrosterone sulfate whereas the liberation of labeled dehydroepiandrosterone was efficiently suppressed in the presence of pregnenolone sulfate. The emerging trend of effective inhibition involves testosterone, estradiol, and possible biochemical precursors including pregnenolone. The inhibition constants of dehydroepiandrosterone {Ki = 7.5 × 10-6 m) and of testosterone {Ki = 7.0 × 10-6 m) for dehydroepiandrosterone sulfate cleavage (Km = 1 × 10-5 m) were comparable with the inhibition constants of preg nenolone (Ki = 8 × 10-6 m) and of testosterone (Ki = 8 × 10-6 m) for pregnenolone sulfate cleavage (Km = 1 × 10-5 m). Cholesteryl sulfate cleavage (Km = 5 × 10-5 m) was inhibited by cholesterol (Ki = 12 × 10-6 m), testosterone (Ki = 7.0 × 10-6 m), and pregnenolone sulfate (Ki = 4 × 10-6 m). The kinetic data in all cases are compatible with competitive inhibition. Whatever the significance of the role of steroid sulfates in steroid hormone production might be, the present studies indicate that an effective control exists for the regulation of hormone synthesis via this pathway. © 1969, American Chemical Society. All rights reserved.