A comparison of cytochrome P450-dependent testosterone 2alpha-hydroxylase in rat (P4502C11) and mouse (P4502alpha).

Hepatic P450 2C11 in the rat and P450(2alpha) in the mouse are unique in being the only isoforms in their respective species with testosterone 2alpha-hydroxylase activity. Comparing gender differences, tissue distribution and physicochemical properties, we investigated whether this uncommon catalytic activity shared by the two isoforms is dependent upon a high degree of homology. Using additional substrates (e.g. androstenedione, hexobarbital), we observed that P450(2alpha) and P450 2C11 produced no metabolites in common. Moreover, concentrations of antisera prepared against purified P450(2alpha) that inhibited 95% of P450(2alpha)-dependent testosterone 2alpha-hydroxylase activity had only a minimal inhibitory effect (< 20%) on P450 2C11-dependent testosterone 2alpha-hydroxylase and were similarly unreactive to the rat isoform isolated on Western blots. Comparison of the isoforms' N-terminal amino acid residues and two internal peptide fragments indicated almost no sequence homology (< 4%). Gender-dependent tissue expression levels of P450(2alpha) and P450 2C11 revealed additional dichotomies. Whereas hepatic P450(2alpha) was moderately female-predominant (M/F; 0.62), hepatic P450 2C11 was clearly male-specific (M/F; 32.9). Murine P450(2alpha) mRNA was equally and substantially expressed in liver, kidney and brain; by contrast earlier studies reported that rat P450 2C11 was exclusively expressed in liver. The present results indicate that the unique testosterone 2alpha-hydroxylase activities of P450(2alpha) and P450 2C11 are expressed by two very different proteins exhibiting minimal homology.