Effect of Oxygen on the Dehalogenation of 1,2-Dibromo-3-Chloropropane by Cytochrome P450cam (CYP101)
G S. Koe, V L. Vilker
Cytochromes P450 are known to exhibit a wide variety of catalytic functions, as well as to possess activity against a large number of hydrocarbon substrates. The determinants of the specific activity(ies) that will operate on a specific substrate have not been widely explored. Earlier, we showed that dehalogenation of 1,2-dibromo-3-chloropropane (DBCP) by P450cam (CYP101) monoxygenase exhibits oxygen- and substrate-dependent product distributions and reaction rates [Koe, G. S., and Vilker, V.L. (1993) Biotechnology Progress. 9, 608-614]. Bromochloroacetone was the major conversion product when incubation media were saturated with oxygen, while allyl chloride was the sole product accounting for virtually all of the DBCP converted in the absence of oxygen. In an effort to develop a quantitative understanding of the effect of oxygen on product distribution and reaction rate, we have identified first generation products and measured reaction rates at four oxygen levels ranging from 0.01% to 100% saturation. In addition to bromochloroacetone and allyl chloride, a number of bromochloropropene isomers were identified in the presence of oxygen, and are thought to be formed by an elimination mechanism. These products accounted for greater than 97-mol% of the reacted DBCP, which was run to high conversion (60-100 mol% DBCP converted). These measurements suggest that P450cam acts on the DBCP substrate through hydroxylation to produce 1-bromo-3-chloroacetone, reduction to produce allyl chloride, and elimination to produce bromochloropropene, with oxygen concentration determining the extent of each activity. A reaction pathway kinetic model that describes the time-varying concentrations of substrate and products quantified the controlling effect of oxygen on these multiple activities. The parameters of the model are compared with independent measurements and measurements form the literature.
bromochloroacetone, cytochromes, oxygen
and Vilker, V.
Effect of Oxygen on the Dehalogenation of 1,2-Dibromo-3-Chloropropane by Cytochrome P450cam (CYP101), Biochemistry
(Accessed September 27, 2023)