Steroid 21-hydroxylase activity in equine ovarian follicles evidenced by isotope dilution-mass spectrometry.
Steroid 21-hydroxylase activity of the microsome-enriched fraction of follicular linings from equine ovaries has been demonstrated by gas chromatography-mass spectrometry. The 21-hydroxylated metabolites were quantified by isotope dilution with deuterated analogues. The two most abundant potential substrates for follicular steroid 21-hydroxylase, progesterone (P) and 17-hydroxyprogesterone (17OHP), were converted respectively to 11-deoxycorticosterone (DOC) and 11-deoxycortisol with corresponding apparent specific activities of 308 and 24 pmol/mg protein/h and apparent Km values of 1.1 and 6.4 microM. Competitive inhibition of the P-to-DOC conversion was exerted by 17OHP and pregnenolone. Hence, the ovarian follicle of the mare is an extraadrenal site of preferential DOC biosynthesis by an enzyme having steroid 21-hydroxylase activity.
Bijault
C
C
Fondation de Recherche en Hormonologie, Fresnes, France.
Dehennin
L
L
D000818:Animals; D001667:Binding, Competitive; D003900:Desoxycorticosterone / Q000378:metabolism; D005260:Female; D015571:Follicular Fluid / Q000378:metabolism; D006736:Horses / Q000502:physiology*; D013058:Mass Spectrometry; D008861:Microsomes / Q000187:drug effects / Q000201:enzymology; D006080:Ovarian Follicle / Q000187:drug effects / Q000201:enzymology*; D010053:Ovary / Q000201:enzymology; D011372:Progestins / Q000494:pharmacology; D011865:Radioisotope Dilution Technique; D012995:Solubility; D013254:Steroid 17-alpha-Hydroxylase / Q000378:metabolism; D013255:Steroid 21-Hydroxylase / Q000378:metabolism*; D013379:Substrate Specificity
D011372:Progestins; D003900:Desoxycorticosterone; D013255:Steroid 21-Hydroxylase; D013254:Steroid 17-alpha-Hydroxylase