ABSORPTION SPECTRAL STUDIES ON HEME LIGAND INTERACTIONS OF P-450(NOR)

Heme-external ligand interactions of P-450(nor) were examined spectrop hotometrically and compared with those of other P-450s. Most nitrogeno us ligands induced type II spectral changes on binding to ferric P-450 (nor), as did other P-450s. In contrast with other P-450s, 2-methylpyr idine and I-butanol induced type I changes in the spectrum of P-450(no r). No spectral interaction of ferrous P-450(nor) with these ligands w as observed. The absorption spectra of the alkyl isocyanide complexes of ferrous P-450(nor) exhibited the Soret peak at 427 nm with a slight shoulder at around 455 nm at neutral pH, and this shoulder was intens ified as the pH was increased, suggesting that the isocyanide complexe s of P-450(nor) existed in two states (the 430 and 455 nm states) whic h were in pi-I-dependent equilibrium in a similar manner to microsomal P-450s. However, the equilibrium was shifted mostly to the 430 nm sta te in the complexes of P-450(nor). The findings suggest that P-450(nor ), especially its ferrous form, has some distinct features from P-450( cam) and microsomal P-450s in the distal heme environment.