Abstract
1. Benzpyrene hydroxylase of human liver biopsies and of livers from four inbred rat strains and from a non-inbred Sprague-Dawley rat strain, rabbit and guinea-pig was studied. 2. The human liver benzpyrene hydroxylase was similar to that of laboratory animals with respect to cofactor requirements, NADPH and O2, microsomal localization and inhibition by CO and N2. 3. Kinetic analysis of human adult benzpyrene hydroxylase indicated the presence of two enzymes, whereas human foetal liver contained only one enzyme hydroxylating 3,4-benzpyrene. Michaelis constants of human liver benzpyrene hydroxylase were slightly higher than Km values of animal liver enzymes. 4. Benzpyrene hydroxylase activity in human liver showed no sex difference, was enhanced by cigarette smoking and was decreased in patients with liver damage. 5. Variation of benzpyrene hydroxylase activity in human liver samples was about 6-fold in the 'control' group and 16-fold when all patients were considered. Variation of benzpyrene hydroxylase activity in inbred rat strains was less than 60% between different individuals and in the non-inbred rat, rabbit and guinea-pig the variation was 2- to 3-fold or less.
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