[Effect of phase transitions in microsomal membranes on energetic characteristics of oxidation]

Naphthalene and aniline oxidation by intact and induced enzyme systems of rat liver microsomes, NADPH and O2 has been studied in a broad temperature range. The oxidation of the same substrates has also been studied in the systems "microsomes--cumene hydroperoxide" and "purified cytochrome P-450--cumene hydroperoxide". The temperature curves of catalytic constants for type I substrate (naphthalene-oxidation) in the system with cofactors is characterized by break on Arrenius dependence near 18--24 degrees C and explained by phase transitions of microsomal membrane lipids. The temperature curves of catalytic constants for type II substrate (aniline-oxidation) in all studied systems do not break on Arrenius plots. Catalytic oxidation contants of both substrates in systems "microsomes--hydroperoxide" and "cytochrome P-450--hydroperoxide" are characterized by constant activation energies in broad temperature range. The results obtained are discussed from the point of view of the effect of phospholipids phase transitions in microsomal membrane on a rate limiting step.