Heme proteins azide binding

Horseradish peroxidase can be inactivated by protein as well as heme modifications. The reaction of horseradish peroxidase with phenylhydrazine is instructive in this regard (Ator and Ortiz de Montellano, 1987). Enzyme inactivation correlates well with covalent binding of 2 equivalents of radiolabeled phenylhydrazine but is associated with conversion of only a small fraction of the prosthetic group to the meso-phenyl adduct. Covalent binding of a metabolite of phenylhydrazine to the protein is therefore primarily responsible for enzyme inactivation, although the identity of the reactive species and the site at which it reacts are not known. The factors that determine whether the heme group (e.g., methylhydrazine, sodium azide) or the protein (e.g., phenylhydrazine) is the primary site of the inactivation reaction also remain elusive. 

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