EVIDENCE FOR SEVERAL DEMETHYLASE ENZYMES IN THE OXIDATION OF DIMETHYLNITROSAMINE AND PHENYLMETHYLNITROSAMINE BY RAT-LIVER FRACTIONS

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  • 1 January 1979
    • journal article
    • research article
    • Vol. 39  (5) , 1587-1591
Abstract
The steady state kinetics and isotope effects were examined for demethylation of dimethylnitrosamine and phenylmethylnitrosamine and their deuterated analogs, using the S-9 fraction, the microsomal pellet and postmicrosomal supernatant from rat livers. The isotope effect (ratio of maximal rates for the deuterated and light substrates) using the S-9 from Long-Evans rat livers was 1.82 for dimethylnitrosamine and 5.38 for phenylmethylnitrosamine. Phenobarbital induced dimethylnitrosane demethylase activity in the microsomal pellet of both Long-Evans and Sprague-Dawley rats but to repress this activity in the postmicrosomal supernatant in the Long-Evans rats, while markedly increasing it in the Sprague-Dawley rats. There was nitrosamine demethylase activity in the so-called pH 5 enzymes and in the supernatant from that preparation. The latter activity shows substantially different characteristics from that found in the other fractions.