Compound I formation is a partially rate-limiting process in chloroperoxidase-catalyzed bromination reactions.
The kinetics of chloroperoxidase-catalyzed bromination and chlorination reactions were studied at various halide and hydrogen peroxide concentrations. At very high concentrations, both chloride (KI = 370 mM) and bromide (KI = 150 mM) are competitive substrate inhibitors versus hydrogen peroxide. Results at subinhibitory halide concentrations for bromination reactions (kcat = 4 ms-1, kcat/KPeroxide = 1.6 microM-1 x s-1 and kcat/KBr = 4.0 microM-1 x s-1) and chlorination reactions (kcat = 1.5 ms-1, kcat/Kperoxide = 2.3 microM-1 x s-1, and kcat/KBr = 0.32 microM-1 x s-1) indicate that halide oxidation is rate-limiting in chlorination reactions. However, in bromination reactions, both compound I formation and bromide oxidation are partially rate-limiting. This is the first documented case where compound I formation participates in determining the overall rate of a peroxidase reaction.
Department of Chemistry, Colby College, Waterville, Maine 04901.
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D001667:Binding, Competitive; D001965:Bromides / Q000378:metabolism*; D002711:Chloride Peroxidase / Q000378:metabolism*; D003510:Cyclohexanes / Q000378:metabolism*; D003512:Cyclohexanones / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000378:metabolism; D007700:Kinetics; D008433:Mathematics; D008962:Models, Theoretical; D010544:Peroxidases / Q000378:metabolism*
D001965:Bromides; D003510:Cyclohexanes; D003512:Cyclohexanones; C006991:chlorodimedone; D006861:Hydrogen Peroxide; D010544:Peroxidases; D002711:Chloride Peroxidase