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Arch Biochem Biophys

Title:		Steroid metabolism by rabbit olfactory-specific P450 2G1
Author(s):		Ding X; Coon MJ;
Address:		"Department of Biological Chemistry, Medical School, University of Michigan, Ann Arbor 48109-0606"
Journal Title:		Arch Biochem Biophys
Year:		1994
Volume:		315
Issue:		2
Page Number:		454 - 459
DOI:		10.1006/abbi.1994.1524
ISSN/ISBN:		0003-9861 (Print) 0003-9861 (Linking)
Abstract:		"Cytochrome P450 2G1 (2G1), which is uniquely expressed in the olfactory mucosa in mammals, may have important physiological functions. In the present study, we have examined the catalytic activity of rabbit 2G1 toward a number of steroid sex hormones, including androstenedione, estradiol, progesterone, testosterone, and 5 alpha-dihydrotestosterone; the purified cytochrome is active toward all of these compounds in a reconstituted enzyme system with turnover numbers of 1.84, 0.34, 1.46, 1.04, and 0.84, respectively, at a substrate concentration of 5 microM. In the presence of cytochrome b5, the turnover numbers are 1.58, 0.66, 1.66, 2.74, and 1.34, respectively. Estradiol is converted to the 2-hydroxy compound (major product) and 4-hydroxy compound (minor product) by 2G1, and progesterone is converted to the 16 alpha-hydroxy derivative as well as the corresponding keto compound as a secondary product. The same products are formed in olfactory microsomal suspensions as major metabolites of progesterone, and the reactions are inhibited strongly by anti-2G1 IgG. In a reconstituted system, 2G1 has an apparent Km of 2.0 microM and a Vmax of 1.8 nmol/min/nmol P450 for the formation of the 16 alpha-hydroxyprogesterone. Of particular interest, 2G1-catalyzed progesterone metabolism is effectively inhibited by the boar pheromones, 5 alpha-androst-16-en-3-one and 5 alpha-androst-16-en-3 alpha-ol, and to a lesser extent by a variety of odorant compounds as well as by known P450 inhibitors, including ketoconazole and alpha-naphthoflavone. The broad substrate specificity and relatively high catalytic efficiency of 2G1 in sex steroid metabolism suggest a role for this unique P450 isozyme in the maintenance of steroid hormone homeostasis in the olfactory mucosa"
Keywords:		Androstenedione/metabolism Animals Benzoflavones/pharmacology Cytochrome P-450 Enzyme Inhibitors Cytochrome P-450 Enzyme System/*metabolism Cytochromes b5/metabolism Dihydrotestosterone/metabolism Estradiol/metabolism Female Ketoconazole/pharmacology Kine;
Notes:		"MedlineDing, X Coon, M J eng DC-01990/DC/NIDCD NIH HHS/ DK-10339/DK/NIDDK NIH HHS/ Research Support, U.S. Gov't, P.H.S. 1994/12/01 Arch Biochem Biophys. 1994 Dec; 315(2):454-9. doi: 10.1006/abbi.1994.1524"