The inhibitory effect of pyrazinamide on microsomal monooxygenase activities is related to the binding to reduced cytochrome P-450

The antitubercular agent Pyrazinamide (PZA) binds to oxidized and reduced rat liver microsomal cytochrome P-450 with the binding characteristics typical of basic heterocyclic compounds. The PZA-cytochrome P-450(Fe2+) interaction, although characterized by rather weak affinity (Ks = 4 × 10-3M), has a PZA-cytochrome P-450(Fe2+) bond of considerable strenght and stability. PZA has an inhibitory effect on the aniline hydroxylase, p-nitroanisole O-demethylase and aminopyrine demethylase activities of rat liver microsomes. The PZA-cytochrome P-450(Fe2+) binding characteristics explain the observed inhibitory effect of the drug on the monooxygenase activities.