title: Mechanism of horseradish peroxidase-catalyzed heme oxidation and polymerization (beta-hematin formation).
abstract: Horseradish peroxidase (HRP) catalyzes the polymerization of free heme (beta-hematin formation) through its oxidation. Heme when added to HRP compound II (FeIV=O) causes spectral shift from 417 nm (Compound II) to 402 nm (native, FeIII) indicating that heme may be oxidized via one-electron transfer. Direct evidence for one-electron oxidation of heme by HRP intermediates is provided by the appearance of an E.s.r signal of a 5,5-dimethyl-1-pyrroline N-oxide (spin trap)-heme radical adduct (a1H=14.75 G, a2H=4.0 G) in E.s.r studies. Heme-polymerization by HRP is inhibited by spin trap indicating that one-electron oxidation product of heme ultimately leads to the formation of heme-polymer. HRP, when incubated with diethyl pyrocarbonate (DEPC), a histidine specific reagent, shows concentration dependent loss of heme-polymerization indicating the role of histidine residues in the process. We suggest that HRP catalyzes the formation of heme-polymer through one-electron oxidation of free heme.
authors.affiliation: Molecular and Structural Biology Division, Central Drug Research Institute, Chatter Manzil Palace, Mahatma Gandhi Marg, Lucknow-226001, Uttar Pradesh, India.
authors.forename: Vishal
authors.initials: V
authors.lastname: Trivedi
authors.forename: Prem
authors.initials: P
authors.lastname: Chand
authors.forename: Prakas R
authors.initials: PR
authors.lastname: Maulik
authors.forename: Uday
authors.initials: U
authors.lastname: Bandyopadhyay
mesh_terms: D002384:Catalysis; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D006418:Heme / Q000378:metabolism*; D006420:Hemeproteins / Q000096:biosynthesis*; D006735:Horseradish Peroxidase / Q000494:pharmacology*; D010084:Oxidation-Reduction; D011108:Polymers / Q000378:metabolism
chemical_list: D005609:Free Radicals; D006420:Hemeproteins; D011108:Polymers; C020753:hemozoin; D006418:Heme; D006735:Horseradish Peroxidase