title: 4-Aminobenzoic acid hydrazide inhibition of microperoxidase-11: catalytic inhibition by reactive metabolites.
abstract: Inhibition of human peroxidase enzymes such as myeloperoxidase or eosinophil peroxidase represents a novel therapeutic area, for which there are no current clinical therapeutics. We utilized 4-aminobenzoic acid hydrazide which was reported to be a potent irreversible inhibitor of myeloperoxidase to gain insight into the role of reactive metabolites in catalytic inhibition. In order to carry out detailed studies, we used a model peroxidase, microperoxidase-11 (MP-11). We investigated the heme spectrum of MP-11 in the presence of 4-ABAH and found that heme bleaching occurred that was irreversible. This coincided with an absence of catalytic activity. The spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) was able to significantly prevent inactivation of peroxidase activity, therefore, we performed ESR spin trapping studies and detected a carbonyl carbon-centered radical of 4-ABAH. In order to determine if the free radical metabolites became bound to MP-11, we performed high-resolution MALDI with elemental analysis to determine the change in elemental composition that occurred in these reactions. These masses were assigned to free radical metabolites of 4-ABAH and were not observed in reactions containing DMPO. We conclude that the 4-ABAH free radical metabolites which were bound to MP-11 were involved in the catalytic inhibition and were scavenged by DMPO.
authors.affiliation: Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, AB, Canada.
authors.forename: Pratik
authors.initials: P
authors.lastname: Arvadia
authors.forename: Malyaj
authors.initials: M
authors.lastname: Narwaley
authors.forename: Randy M
authors.initials: RM
authors.lastname: Whittal
authors.forename: Arno G
authors.initials: AG
authors.lastname: Siraki
mesh_terms: D002384:Catalysis; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D010544:Peroxidases / Q000037:antagonists & inhibitors*; D013113:Spin Labels
chemical_list: D004791:Enzyme Inhibitors; D013113:Spin Labels; D010544:Peroxidases; C021799:microperoxidase