Multiple Forms of Cytochrome P-450 in kidney Cortex Microsomes of Rabbits Treated with 3-Methylcholanthrene1

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Abstract
Cytochrome P-450 was purified from kidney cortex microsomes of rabbits treated with 3-methylcholanthrene. 6-Amino- n -hexyl-Sepharose 4B column chromatography of the cholate-solubilized microsomes yielded two cytochrome P-450 fractions, one of which was eluted from the column with 20 m m potassium phosphate buffer in the presence of 0.4% cholate and 0.08% Emulgen 913. This fraction was partially purified to a specific content of 4.49 nmol of cytochrome P-450/mg of protein. This P-450 fraction catalyzed myristate ω- and (ω-1)-hydroxylation with a turnover rate of 5.0 nmol/nmol of cytochrome P-450 in a reconstituted system containing NADPH-cytochrome c reductase, cytochrome b 5 and phosphatidylethanolamine. It had no benzo(a)pyrene hydroxylation activity. The other cytochrome P-450 fraction, which was eluted from the column with 0.1 m potassium phosphate buffer in the presence of 0.4% cholate and 0.08% Emulgen 913, was purified to a specific content of 12.0 nmol of cytochrome P-450/mg of protein. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of the final preparation gave a major polypeptide band with a molecular weight of 58, 000. This cytochrome P-450 showed a maximal peak at 448 nm in the carbon monoxide difference spectrum of its reduced form. Its absolute spectrum of the oxidized form had low-spin characteristics. It catalyzed benzo(a)-pyrene hydroxylation with a turnover rate of 3.63 nmol/nmol of cytochrome P-450 in a reconstituted system containing NADPH-cytochrome c reductase and phosphatidylcholine, whereas little myristate hydroxylation activity was detected. The results demonstrate the occurrence of multiple forms of cytochrome P-450 in rabbit kidney cortex microsomes.

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