Inactivation of rabbit pulmonary cytochrome P-450 in microsomes and isolated perfused lungs by the suicide substrate 1-aminobenzotriazole.

The autocatalytic destruction of pulmonary cytochrome P-450 (P-450) by 1-aminobenzotriazole (ABT) was investigated in microsomes and in isolated perfused lungs from untreated and beta-naphthoflavone-induced rabbits. Microsomal benzphetamine N-demethylase (BND) and 7-ethoxyresorufin O-deethylation (ERF) activities, catalyzed by P-450 isozymes 2 and 6, respectively, and specific P-450 content were determined after incubation with ABT. In vitro destruction of P-450 was dependent on ABT concentration and required NADPH. Significant losses of BND and ERF activities were observed only at ABT concentrations above 10 microM. Percent losses of BND and ERF activities equaled those of total P-450 at 1 mM and surpassed them at 10 mM. The time and concentration dependence of the destruction of P-450 by ABT was investigated in isolated perfused rabbit lungs. The percent loss of total P-450 increased with increasing ABT concentration (18 +/- 8% loss at 1 microM to 85 +/- 4% at 10 mM). Although extensive losses of P-450 occurred after perfusion with 10 mM ABT for 60 min, no ABT-dependent losses of flavin-containing monooxygenase activity were observed under these conditions. Percent losses of BND activity in these experiments were similar to those of total P-450 at 1 and 10 mM ABT but were less than P-450 losses at 0.01 and 0.1 mM ABT. Losses of ERF activity in lungs from beta-naphthoflavone-pretreated animals were also substantial and dependent upon perfusion time. Perfusion with 1 mM ABT for 2 to 60 min resulted in time-dependent losses of P-450 (42.8 +/- 7.2% at 2 min to 70.5 +/- 2.5% at 60 min) with equal or somewhat lesser diminishment of BND and ERF activities.(ABSTRACT TRUNCATED AT 250 WORDS)