A Comparison of Cytochrome P450-Dependent Testosterone 2α-Hydroxylase in Rat (P450 2C11) and Mouse (P4502α)

Abstract

Hepatic P₄₅₀ 2C11 in the rat and P_4502α in the mouse are unique in being the only isoforms in their respective species with testosterone 2α-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 P_4502α and P₄₅₀ 2C11 produced no metabolites in common. Moreover, concentrations of antisera prepared against purified P_4502α that inhibited 95% of P_4502α-dependent testosterone 2α-hydroxylase activity had only a minimal inhibitory effect (<20%) on P₄₅₀ 2C11-dependent testosterone 2α-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 P_4502α and P₄₅₀ 2C11 revealed additional dichotomies. Whereas hepatic P_4502α was moderately female-predominant (M/F; 0.62), hepatic P₄₅₀ 2C11 was clearly male-specific (M/F; 32.9). Murine P_4502α 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 2α-hydroxylase activities of P_4502α and P₄₅₀ 2C11 are expressed by two very different proteins exhibiting minimal homology.