[The nature of the rate-limiting step in aniline hydroxylation involving cytochrome P-450 from rat liver microsomes].

The kinetics of aniline hydroxylation with: 1) rat liver microsomes involving NADPH and O2 (System I); 2) hepatic microsomes and tertiary butylhydroperoxide (System II) and 3) microsomes and cumyl hydroperoxide (System III) within 15--37 degrees C has been studied. The reactions were characterized by the values of the aniline oxidation rate constants, k2=v/[E]0, where [E]0 is the initial concentration of cytochrome P--450: k1 2=1,60.10(8) exp (--13400/RT) sec-1., k2 2=1,66.10(9) exp (--14500/RT) sec-1., k3 2=6,83.10(9) exp (--15300/RT) sec-1. The values of delta H* and delta S* were calculated and compared for these three systems. A conclusion is drawn that the act of oxygen insertion into the substrate molecule is the rate-limiting step in the reaction of aniline oxidation for the mentioned system.