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Updated: Jul 4, 2026

Fast and Specific Assessment of the Halogenating Peroxidase Activity in Leukocyte-enriched Blood Samples
Published on: July 28, 2016
Direct examination of H2O2 activation by a heme peroxidase
Justine P Roth1, Christopher J Cramer
1Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, USA. jproth@jhu.edu
Abstract:
Described here is the application of oxygen isotope fractionation together with computational methods, to elucidate a mechanism of enzymatic H2O2 activation. Horseradish peroxidase (HRP) has been the subject of intensive experimental and computational studies, yet questions remain as to the reversibility of the O-O cleavage step. New insight is afforded by the competitive oxygen kinetic isotope effect (18O KIE) upon H2O2 consumption determined under turnover conditions. The 18O KIE is compared to isotope effects calculated for the O-O heterolysis transition state and potential intermediates using density functional theory. In addition, experiments in enriched water provide evidence for HRP-catalyzed scrambling of the 18O label into the unreacted H2O2. The results provide an unprecedented view of H2O2 activation by a heme peroxidase and challenge the assumption of rate-limiting O-O heterolysis.
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