Species differences in benzene hydroxylation to phenol by pulmonary and hepatic microsomes

The metabolism of benzene to phenol by microsomal preparations from lung and liver has been compared in hamsters, rats, and rabbits. There were wide differences in the apparent Vmax of benzene hydroxylation among the various species and tissues and smaller differences in the apparent KM values for benzene hydroxylase. Benzene can inhibit its own metabolism in vitro when present in high concentrations. Phenol was the only metabolite of benzene identified, under the conditions of the assay, in incubation mixtures containing microsomes from lung or liver of any of the three animal species. When incubated with microsomes under the conditions used to measure benzene metabolism, phenol was further metabolized in liver but not in lung preparations. Phenol metabolism was almost completely inhibited when 11.2 mM benzene was included in the incubation mixture containing hepatic microsomes. The variation in rates of benzene hydroxylation by microsomal preparations from lungs or livers of the three animal species was similar to the variation in rates of benzypyrene hydroxylation in the same preparations.