title: Spectroscopic and QM/MM investigations of Chloroperoxidase catalyzed degradation of orange G.
abstract: Chloroperoxidase (CPO), a heme-thiolate protein, from Caldariomyces fumago catalyzes a plethora of reactions including halogenation, dismutation, epoxidation, and oxidation. Although all CPO-catalyzed reactions go through a common intermediate, compound I, different mechanisms are followed in subsequent transformations. To understand the mechanism of CPO-catalyzed halide-dependent degradation of orange G, the role of halide and pH was systematically investigated. It is revealed that formation and protonation of compound X, a long-sought after hypochlorite heme adduct intermediate existed during CPO-catalyzed halide-dependent reactions, significantly lowers the reaction barrier and increases the efficiency of CPO-catalyzed orange G degradation. The extremely acidic optimal reaction pH suggests the protonation of a residue, presumably, Glu 183 in CPO catalysis. Halide dependent studies showed that Kcat is higher in the presence of Br(-) than in the presence of Cl(-). The degradation products of orange G indicate the cleavage at a single position of orange G, demonstrating a high regioselectivity of CPO-catalyzed degradation. Based on our kinetic, NMR and QM/MM studies, the mechanism of CPO-catalyzed orange G degradation was proposed.
authors.affiliation: Department of Chemistry & Biochemistry, Florida International University, Miami, FL 33199 USA.
authors.forename: Rui
authors.initials: R
authors.lastname: Zhang
authors.affiliation: Department of Chemistry & Biochemistry, Florida International University, Miami, FL 33199 USA.
authors.forename: Qinghao
authors.initials: Q
authors.lastname: He
authors.affiliation: School of Chemistry and Chemical Engineering, Xianyang Normal University, Xianyang, 712000 China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Huang
authors.affiliation: Department of Chemistry & Biochemistry, Florida International University, Miami, FL 33199 USA. Electronic address: wangx@fiu.edu.
authors.forename: Xiaotang
authors.initials: X
authors.lastname: Wang
mesh_terms: D001203:Ascomycota / Q000201:enzymology*; D001391:Azo Compounds / Q000737:chemistry*; D002384:Catalysis; D002711:Chloride Peroxidase / Q000737:chemistry*; D005656:Fungal Proteins / Q000737:chemistry*; D007700:Kinetics; D008956:Models, Chemical; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods
chemical_list: D001391:Azo Compounds; D005656:Fungal Proteins; C008710:Orange G; D002711:Chloride Peroxidase
keywords: Azo dye; Biodegradation; Chloroperoxidase; Compound X; Halide dependent; Heme protein