Kinetic characterization of compound I formation in the thermostable cytochrome P450 CYP119.

The kinetics of formation and breakdown of the putative active oxygenating intermediate in cytochrome P450, a ferryl-oxo-(pi) porphyrin cation radical (Compound I), have been analyzed in the reaction of a thermostable P450, CYP119, with meta-chloroperoxybenzoic acid (m-CPBA). Upon rapid mixing of m-CPBA with the ferric form of CYP119, an intermediate with spectral features characteristic of a ferryl-oxo-(pi) porphyrin cation radical was clearly observed and identified by the absorption maxima at 370, 610, and 690 nm. The rate constant for the formation of Compound I was 3.20 (+/-0.3) x 10(5) m(-1) s(-1) at pH 7.0, 4 degrees C, and this rate decreased with increasing pH. Compound I of CYP119 decomposed back to the ferric form with a first order rate constant of 29.4 +/- 3.4 s(-1), which increased with increasing pH. These findings form the first kinetic analysis of Compound I formation and decay in the reaction of m-CPBA with ferric P450.