title: The distal glutamic acid as an acid-base catalyst in the distal site of horseradish peroxidase.
abstract: The distal His is an essential amino acid residue as a general acid-base catalyst for peroxidase reaction cycle. However, the x-ray structure of chloroperoxidase revealed that Glu is located near the heme, suggesting that the carboxyl group also assists cleavage of O-O bond in peroxides. In this paper, we examined functional and structural properties of a horseradish peroxidase mutant having Glu instead of the distal His. Although this amino acid replacement depressed reaction rate with H2O2 and oxidation activity for guaiacol, the mutant still exhibited much higher activity than mutants in which the distal His was replaced by hydrophobic amino acid. Kinetic measurements suggest that the proton abstraction is decelerated in the mutant due to large fluctuation of the carboxyl group of the distal Glu. Therefore, we can conclude that Glu can be a potent acid-base catalyst for peroxidase reaction cycle, if the carboxyl group can be fixed at the optimum position.
authors.affiliation: Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Tanaka
authors.forename: K
authors.initials: K
authors.lastname: Ishimori
authors.forename: I
authors.initials: I
authors.lastname: Morishima
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002711:Chloride Peroxidase / Q000737:chemistry; D018698:Glutamic Acid; D006139:Guaiacol; D006418:Heme; D006639:Histidine; D006735:Horseradish Peroxidase / Q000737:chemistry* / Q000378:metabolism*; D006861:Hydrogen Peroxide; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D016297:Mutagenesis, Site-Directed; D010084:Oxidation-Reduction; D016133:Polymerase Chain Reaction; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013053:Spectrophotometry
chemical_list: D011994:Recombinant Proteins; D018698:Glutamic Acid; D006418:Heme; D006639:Histidine; D006139:Guaiacol; D006861:Hydrogen Peroxide; D006735:Horseradish Peroxidase; D002711:Chloride Peroxidase