title: 3 beta-hydroxysteroid isomerase dehydrogenase in guinea-pig kidney: possible involvement in 11-deoxycorticosterone formation in situ.
abstract: 3 beta-Hydroxysteroid isomerase dehydrogenase, capable of acting on C21- and C19-3 beta-hydroxy-5-ene-steroids has been found in guinea-pig kidney at equivalent levels to those in guinea pig testes. Of the 3 beta-hydroxy-5-ene-steroids present in guinea pig serum, 21-hydroxypregnenolone occurs in highest concentration (17 nM) followed by pregnenolone (10 nM), whereas 17 alpha-hydroxy-pregnenolone and dehydroepiandrosterone occur in very low concentrations (less than 0.5 nM). Furthermore, the concentration of 21-hydroxypregnenolone relative to 11-deoxycorticosterone (the mineralocorticoid of the guinea pig), is 10:1 (Nishikawa and Strott, Steroids 41 (1983) 105-120). The apparent Km value for 21-hydroxypregnenolone, for the reaction yielding 11-deoxycorticosterone as catalysed by guinea pig kidney microsomes, was 85 nM and the Vmax 33 pmol/min per mg protein. Pregnenolone was a competitive inhibitor (apparent Ki = 5 microM) in the above reaction. A sex difference in the level of the enzyme in the kidney was found (activity in the female was one-third of that in the male) which may indicate that the enzyme is under partial androgen control. 3 beta-Hydroxysteroid isomerase dehydrogenase activity was also detected in guinea pig liver and again it was lower in the female. Whilst the exact role of 3 beta-hydroxysteroid isomerase dehydrogenase in guinea-pig kidney remains uncertain, the data suggest that it may utilise blood-borne 21-hydroxypregnenolone, the later then playing the role of a prohormone.
mesh_terms: D015067:17-Hydroxysteroid Dehydrogenases / Q000032:analysis; D015096:3-Hydroxysteroid Dehydrogenases / Q000032:analysis*; D000818:Animals; D003900:Desoxycorticosterone / Q000096:biosynthesis*; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007668:Kidney / Q000201:enzymology*; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008297:Male; D011375:Progesterone Reductase / Q000032:analysis*; D013737:Testis / Q000201:enzymology
chemical_list: D003900:Desoxycorticosterone; D015067:17-Hydroxysteroid Dehydrogenases; D015096:3-Hydroxysteroid Dehydrogenases; D011375:Progesterone Reductase; C032690:3-alpha-(17-beta)-hydroxysteroid dehydrogenase (NAD(+))