Chemical modification of cytochrome P-450 LM2 with N-acetylimidazole. Evidence for the functional involvement of tyrosyl residues.

Cytochrome P-450 LM2 has been reacted with N-acetylimidazole. About three tyrosyl residues of cytochrome P-450 LM2 are accessible to O-acetylation. The analysis of the spectral dissociation constants, substrate binding kinetics, reduction kinetics, N-demethylase activity and substrate conversion by artificial oxygen-donating agents of differently acetylated enzyme provides evidence for the existence of two groups of accessible tyrosines. One tyrosyl residue is located in the immediate environment of the heme iron and is involved in the binding of type II substrates. This tyrosine is not necessary for N-demethylation. Acetylation of two further tyrosyl residues, however, causes an almost complete inhibition of enzymatic activity. The results strongly suggest tyrosine(s) to be involved in NADPH-cytochrome P-450 reductase dependent N-demethylation.