2-ethynylnaphthalene as a mechanism-based inactivator of the cytochrome P-450 catalyzed N-oxidation of 2-naphthylamine.

Since the N-oxidation of several carcinogenic arylamines has been shown to be catalyzed preferentially by cytochrome P-450IA2 in several species, homologous ethynyl-substituted aromatic hydrocarbons, 2-ethynylnaphthalene, 1-ethynylnaphthalene, and 2-ethynylfluorene, were synthesized and examined as potential mechanism-based inactivators of this monooxygenase. By use of 2-naphthylamine, whose N-oxidation was known to be selectively catalyzed by rat cytochrome P-450ISF-G (P-450IA2), and hepatic microsomes from isosafrole-treated rats, each of these ethynyl derivatives was found to be strongly inhibitory at concentrations of 1 and 10 microM. However, only inhibition by 2-ethynylnaphthalene was significantly enhanced by prior incubation with the microsomal system. The inactivation of 2-naphthylamine N-oxidation was found to be NADPH- and time-dependent and to follow pseudo-first-order kinetics, demonstrating that 2-ethynylnaphthalene is a potent mechanism-based inactivator of the enzymatic activity. The extrapolated kinactivation and KI were 0.23 min-1 and 8 microM, respectively. By use of 2-aminofluorene, whose N-oxidation was known to be catalyzed by both cytochromes P-450ISF-G and P-450 beta NF-B (P-450IA1), and the purified enzymes in a reconstituted system, both 2-ethynylnaphthalene and 1-ethynylnaphthalene were found to be strongly inhibitory. However, 2-ethynylnaphthalene was a more potent inhibitor of the purified P-450ISF-G than of P-450 beta NF-B; and it was also found to be a more potent inhibitor of P-450ISF-G than was 1-ethynylnaphthalene.(ABSTRACT TRUNCATED AT 250 WORDS)