Purification and characterization of liver microsomal cytochrome P-450 from untreated male rats.

Different forms of cytochrome P-450 from untreated male rats were simultaneously purified to homogeneity using the HPLC technique. The absorption maximum, molecular weight, NH2-terminal sequence and catalytic activity of them were determined. The NH2-terminal sequences of six forms of cytochrome P-450 (designated P450 UT-1, UT-2, UT-4, UT-5, UT-7 and UT-8) indicate that these cytochrome P-450 isozymes are of different molecular species. The hydrophobicity values of the NH2-terminal sequences of P450 UT-1 and P450 UT-8 were lower than that of other forms. P450 UT-8 has the highest molecular weight, 54,000, of the six forms of P-450. P450 UT-2 was active in demethylation of benzphetamine, P450 UT-4 was active in the metabolism of 7-ethoxycoumarin and p-nitroanisole. P450 UT-1 and P450 UT-2 were active in the 2 alpha- and 16 alpha-hydroxylation of testosterone, whereas P450 UT-4 was active in the 6 beta-, 7 alpha- and 15 alpha-hydroxylation of the same steroid. We believe that P450 UT-1, P450 UT-7 and P450 UT-8 are as yet unrecognized forms of cytochrome P-450.