Reaction of Carbon-Monoxide and Molecular-Oxygen with P450terp (CYP108) and P450BM-3 (CYP102)

The kinetics and equilibrium of carbon monoxide binding and the reaction of autodecomposition of oxy-complexes of two bacterial P450sP450BM-3 and P450terphave been studied and compared with the corresponding properties of P450cam and some of the microsomal P450s. The second-order reaction rate constants for the reaction of P450terp and P450BM-3 with carbon monoxide in the absence of substrate at 5°C were 3.6 × 106 and 1.6 × 106 M−1 s−1, respectively. The presence of the physioIogical substrate markedly influenced the rate of carbon monoxide binding with P450terp, decreasing the rate constant by approximately 100-fold, and did not have a significant effect on carbon monoxide binding with P450BM-3. The reaction of carbon monoxide with both cytochromes was monophasic in the absence or in the presence of substrate. The carbon monoxide binding enthalpy change was very small for P450BM-3 (−0.2 kcal mol−1) and more negative for P450terp (−3.2 kcal mol−1). The rate constants of decomposition of oxy-P450terp and oxy-P450BM-P (heme domain of P450BM-3) at 5°C were 7.1 × 10−4 and 2.5 × 10−2 s−1, respectively. Raising the temperature to 20°C resulted in 24- and 9-fold increase of decomposition of oxy-complexes of P450terp and P450BM-P, respectively. The kinetic properties of the binding reaction of diatomic gases to P450cam, P450terp, and P450BM-3 are consistent with the structures of their active sites.