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Steroid Hydroxylations by Human Adrenal Cortex Microsomes^1,,2

Department of Pediatrics and the Clinical Study Center, University of Texas Medical Branch Galveston, Texas 77550

Address reprint requests to George T. Bryan, M.D., Office of the Dean of Medicine, University of TexasMedical Branch, Galveston, Texas 77550.

Microsomes were prepared from human adrenals obtained at the time of cadaveric renal transplantation. Microsomes were assayed for cytochrome P-450 concentrations (mean = 0.63 nmol/mg protein) and NADPH-cytochrome c reductase activity (mean 65 nmol x min^–1 x mg^–1 protein). Rates of steroid hydroxylation were measured. In man, the rate of 21-hydroxylation of 17-hydroxyprogesterone was approximately three times the rate of 21-hydroxylation of progesterone. The rate of 17-hydroxylation of progesterone was approximately three times the rate of 21-hydroxylation of progesterone. Substrate binding to microsomes showed a type I spectrum with progesterone and 17-hydroxyprogesterone. Both substrates bound all spectrally identifiable sites. Antibody prepared against porcine NADPH-cytochrome c reductase inhibited concomitantly human reductase, 21-hydroxylation of progesterone and 17-hydroxyprogesterone, and 17-hydroxylation of progesterone.

These results were compared to previous studies with beef adrenal microsomes. No specific evidence was obtained to suggest multiple forms of 21-hydroxylase in human adrenal microsomes. It appears as though the human adrenal microsomal cytochrome P-450 electron transport chain is immunologically similar to those studied previously–beef adrenal, and rat and human liver.

¹ Supported by grants RR-73, General ClinicalResearch Centers Program, and AM-07616, of theNational Institutes of Health, and by a John and MaryR. Markle Foundation Scholarship.

² Portions of this work were presented at the AnnualMeeting of the Southern Society for Pediatric Research,New Orleans, January, 1974. (Clinical Research XXII,79A, 1974.)

Received October 15, 1974.