Comparative study on oxidation of aromatic compounds by rat liver and rabbit lung microsomes

A systematic comparative investigation of the kinetics of naphthalene hydroxylation by rabbit lung and rat liver microsomes has been carried out over a temperature range of 4-40 degrees C. A higher catalytic activity of cytochrome P-450 from rabbit lung to naphthalene as compared to rat liver microsomes has been stated. The temperature dependence of naphthalene hydroxylation is characterized by a break in the Arrhenius plot for the enzyme systems of liver microsomes from rats untreated and treated with phenobarbital (PB) and 3-methylcholanthrene (MC), respectively, whereas no such break is observed when aniline is oxidized by rat liver microsomes in combination with NADPH and O2, and also in the cumene hydroperoxide supported (CHP) aniline hydroxylation involving highly purified cytochrome P-450 LM2. A break in the Arrhenius plot is also observed for maximal rates of the naphthalene hydroxylation by lung microsomes from untreated and PB-treated rabbits, whereas for MC-induced lung microsomes it is absent. Glycerol eliminates this break in the Arrhenius plot while propranolol shifts the break point by 3-4 degrees C. The data obtained are discussed in terms of the physical state of microsomal phospholipids and their effect on the components of the hydroxylating system.