Purification and characterization of human liver cytochrome P-450-ALC

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Abstract

Cytochrome P-450-ALC, an ethanol-oxidizing form of microsomal cytochrome P-450 (P-450), has been purified from human liver. P-450-ALC (Mr = 54,000 daltons) is a low-spin ferric hemeprotein with a CO-reduced Soret maximum at 452 nm, and has an NH2-terminal amino acid sequence nearly identical to that deduced from a human P-450-ALC cDNA clone. In a reconstituted system, P-450-ALC oxidizes ethanol and aniline at turnover rates (12.2 and 7.3 nmol min−1, respectively) 10-fold greater than two other human P-450 isozymes (termed P-450-B and P-450-C) purified from the same liver. Both P-450-ALC and P-450-C effectively demethylate N-nitrosodimethylamine (NDMA) at low substrate concentrations (0.5 mM), especially in the presence of cytochrome b5. Our results provide direct evidence for a liver P-450 isozyme in humans with catalytic properties similar to the related alcohol-inducible rodent P-450s and also reveal a new human NDMA demethylase.

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    This work was supported by Grants AA-06371, New investigator Research Award AA-03508 (J.M.L.), and AA-05934 from the NIH, and by Smith, Kline & French, the Ben Franklin Partnership Fund, and the Veterans Administration.

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