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Title: Evidence for heme oxygenase activity in a heme peroxidase.
Authors: Badyal, SK
Eaton, G
Mistry, S
Pipirou, Z
Basran, J
Metcalfe, CL
Gumiero, A
Handa, S
Moody, PC
Raven, EL
First Published: 9-Jun-2009
Citation: BIOCHEMISTRY, 2009, 48 (22), pp. 4738-4746
Abstract: The heme peroxidase and heme oxygenase enzymes share a common heme prosthetic group but catalyze fundamentally different reactions, the first being H(2)O(2)-dependent oxidation of substrate using an oxidized Compound I intermediate, and the second O(2)-dependent degradation of heme. It has been proposed that these enzymes utilize a common reaction intermediate, a ferric hydroperoxide species, that sits at a crossroads in the mechanism and beyond which there are two mutually exclusive mechanistic pathways. Here, we present evidence to support this proposal in a heme peroxidase. Hence, we describe kinetic data for a variant of ascorbate peroxidase (W41A) which reacts slowly with tert-butyl hydroperoxide and does not form the usual peroxidase Compound I intermediate; instead, structural data show that a product is formed in which the heme has been cleaved at the alpha-meso position, analogous to the heme oxygenase mechanism. We interpret this to mean that the Compound I (peroxidase) pathway is shut down, so that instead the reaction intermediate diverts through the alternative (heme oxygenase) route. A mechanism for formation of the product is proposed and discussed in the light of what is known about the heme oxygenase reaction mechanism.
DOI Link: 10.1021/bi900118j
eISSN: 1520-4995
Type: Journal Article
Appears in Collections:Published Articles, Dept. of Chemistry

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