Abstract
The temperature dependence of the rate constant for substrate oxidation by the dehaloperoxidase-hemoglobin (DHP) of Amphitrite ornata has been measured from 278 to 308 K. The rate constant is observed to increase over this range by approximately a factor of 2 for each 10 °C temperature increment. An analysis of the initial rates using a phenomenological approach that expresses the peroxidase ping-pong mechanism in the form of the Michaelis-Menten equation leads to an interpretation of the effects in terms of the fundamental rate constants. The analysis of kinetic data considers a combination of diffusion rate constants for substrate and H(2)O(2), elementary steps involving activation and heterolysis of the O-O bond of H(2)O(2), and two electron transfers from the substrate to the iron. To complete the analysis from the perspective of turnover of substrate into product, density function theory (DFT) calculations were used to address the fate of phenoxy radical intermediates. The analysis suggests a dominant role for diffusion in the kinetics of DHP.
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