Testosterone 17- hydroxylation

Hanioka N, Gonzalez FJ, Lindberg NA, et al. Site-directed mutagenesis of cytochrome P450s CYP2A1 and CYP2A2 influence of the distal helix on the kinetics of testosterone hydroxylation. Biochemistry 1992 31(13) 3364—3370. 

Carbon monoxide inhibited the 6/3-. la-, and 16a-hydroxylation of testosterone by rat liver microsomes to different extents. A C0/02 ratio of 0.5 inhibited the la-, 6/i-, and 16a-hydroxylation reactions by 14%, 25%, and 36%, respectively, and the ratio of C0/02 needed for 50% inhibition of testosterone hydroxylation in the 16a-, 6/3-, and 7a-positions was 0.93, 1.54, and 2.36, respectively (36,48). Studies on the photochemical action spectrum revealed that CO inhibition of the three hydroxylation reactions was maximally reversed by monochromatic light at 450 nm, but there were differences in the shape of the photochemical reactivation spectra for the 6/3-, la-, and 16a-hydroxylation reactions (36,48). The data from our laboratory summarized above and at the First International Symposium on Microsomes and Drug Oxidation in 1968 pointed to multiple cytochromes P450 with different catalytic activities that were under separate regulatory control (36,45,46), and we indicated that the actual number of cytochromes that participate in the multiple hydroxylation reactions must await the solubilization and purification of the microsomal system (36). The use of different inducers of liver microsomal monooxygenases caused selective increases in the concentration of specific cytochromes P450 in fiver microsomes that greatly facilitated the isolation and purification of these hemoproteins. 

P450 gene designations are based on the systematic nomenclature of ref. [23]. Table is modified from ref. [24]. The major sites of testosterone hydroxylation catalyzed by the individual P450 proteins are shown. Testosterone metabolites specific to the P450 s activity in rat liver microsomal incubations are underlined. Based on refs [8], [11], [21], [25], [26] and references therein. 

Purified CYP2C13 exhibits high testosterone hydroxylase activity in a reconstituted enzyme system, but this enzyme makes only marginal contributions to liver microsomal testosterone hydroxylation. ... 

CYP4A2 catalyzes fatty acid w-hydroxylation, but does not catalyze testosterone hydroxylation. 15p-hydroxyIation of steroid sulfates. CYP2C12 also catalyzes weak testosterone I5a- and la-hydroxylase activities. 

Sonderfan, A.J., M.P. Arlotto, D.R. Dutton, S.K. McMillen, and A. Parkinson (1987). Regulation of testosterone hydroxylation by rat liver microsomal cytochrome P-450. Arch. Biochem. Biophys. 255, 27-41. 

Yamazaki, H. and T. Shimada (1997). Progesterone and testosterone hydroxylation by cytochromes P450 2C19, 2C9, and 3A4 in human liver microsomes. j4nc/i. Biochem. Biophys. 346, 161-169. 

Ballard SA, Lodola A, Tarbit MH. A comparative study of 1-substituted imidazole and 1,2,4-triazole antifungal compounds as inhibitors of testosterone hydroxylations catalysed by mouse hepatic microsomal cytochromes P-450. Biochem Pharmacol 1988 37 4643-4651. 

Lee SJ, Goldstein JA (2012) Comparison of CY-P3A4 and CYP3A5 the effects of cytochrome and NADPH-cytochrome P450 reductase on testosterone hydroxylation activities. Drug Metab Pharmacokinet 27 663-667... 

CYP4A2 catalyzes fatty acid co-hydroxylation, but it does not catalyze testosterone hydroxylation... 

Sonderfan AJ, Arlotto MP, Dutton DR, McMillen SK, Parkinson A (1987) Regulation of testosterone hydroxylation by rat liver mierosomal cytochrome P-450. Arch Bioehem Biophys 255 27-41... 

MgCl2 (10 mM) increased the apparent Km (83 to 173 /am) and reduced the Vjnax (3.4 to 2.4 min-1) of triazolam 4-hydroxylation by expressed CYP3A4 [21]. However, both MgCl2 (30 mM) and CaCl2 (30 mM) significantly increased reaction rates of testosterone 6/3-hydroxylation (approximately threefold) and nifedipine oxidation (three- to six-fold) by human liver microsomes (HLMs) or recombinant CYP3A4 (reconstituted with b5 and GSH) [15]. It was suggested that divalent cation stimulation on the activity was related to involvement of b5 in CYP 3A4 reaction. 

There are comparatively few studies addressing the structure-metabolism relationships of phosphoric acid monoester hydrolysis. For example, kinetics of decomposition in rat whole blood were examined for the phosphoric acid monoesters of estrone, 17a- and 17/J-testosterone, 3-(hydroxyme-thyl)phenytoin (see Fig. 9.7,a), and 1-phenylvinyl alcohol (9.28, the enolic form of acetophenone) [87]. As a general trend, the rate of hydrolysis increased with the acidity of the leaving hydroxylated compound. In other words, hydrolysis was the fastest for the phosphoric acid aryl monoester (estrone 3-phosphate), and slowest for the two testosterone phosphoric acid... 

A highly modified methyl testosterone derivative also exhibits antiandrogenic activity. One synthesis of this compound involves initial alkylation of methyl testosterone (35) by means of strong base and methyl iodide to afford the 4,4-dimethyl derivative 6. Formylation with alkoxide and methyl formate leads to the 2-hydroxymethyl derivative 37. Reaction of this last with hydroxyl amine leads to formation of an isoxazole ring. There is then obtained azastene (38) . 

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