[Spectral interactions of cytochrome P-450 with n-heptane and methanol]

Methanol interacts with cytochrome P-450 to produce the reversed type I spectral change. In the presence of type I substrate n-heptane, the methanol induced spectrum disappears without detectable effects of interaction suggesting that methanol is a very weak ligand for heme iron of cytochrome P-450. Methanol strongly lowers the apparent spectral dissociation constant (Ks app) of n-heptane binding with rat liver cytochrome P-450 both in control and C6-C9 petroleum fraction inhaled group. In control group, titration of cytochrome P-450 with methanolic solutions of n-heptane does not change the maximal spectral interaction (Amax) observed with pure n-heptane. However in the inhaled group during titration of induced cytochrome P-450 with methanolic solutions of n-heptane an additional type I spectral change is observed. Thus addition of "equivalent" amounts of methanol into the reference cuvette during titration with methanolic solutions overestimates the true magnitude of type I spectral change of cytochrome P-450 with n-heptane.