Characterization of pirenzepine interaction with cytochrome P-450.

Pirenzepine interacts with the haem iron of cytochrome P-450 from rat-and pig-liver microsomes, to give absorption spectra with max. at 424-429 nm, and min. at 391-399 nm. Binding to cytochrome P-450 was not detected with human-liver microsomes. Inhibition of 7-ethoxycoumarin dealkylation by pirenzepine using rat-liver microsomes gave values of I50 = 5 mM and Kis = 0.53 mM. E.p.r. spectra showed that pirenzepine probably interacts with the haem iron through the pirenzepine N-4(1) tertiary amine group.