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 degrees C mere 3.6 X 10(6) and 1.6 X 10(6) 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 degrees C were 7.1 X 10(-4) and 2.5 X 10(-2) s(-1), respectively. Raising the temperature to 20 degrees 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. (C) 1945 Academic Press, Inc.