title: Kinetic and spectral properties of pea cytosolic ascorbate peroxidase.
abstract: Sufficient highly purified native pea cytosolic ascorbate peroxidase was obtained to characterize some of its kinetic and spectral properties. Its rate constant for compound I formation from reaction with H2O2 is 4.O x 10(7) M-1 s-1, somewhat faster than is typical for peroxidases. Compound I has the typical optical spectrum of an iron(IV)-porphyrin-pi-cation radical, despite considerable homology with yeast cytochrome c peroxidase. The rate constant for compound I reduction by ascorbate is extremely fast (8.0 x 10(7) M-1 S-1 at pH 7.8), again in marked contrast to the behavior of the yeast enzyme. The pH-rate profile for compound I formation indicates a pKa value of 5.0 for a group affecting the active site reaction.
authors.affiliation: Department of Biochemistry, University of Alberta, Edmonton, Canada.
authors.forename: L A
authors.initials: LA
authors.lastname: Marquez
authors.forename: M
authors.initials: M
authors.lastname: Quitoriano
authors.forename: B A
authors.initials: BA
authors.lastname: Zilinskas
authors.forename: H B
authors.initials: HB
authors.lastname: Dunford
mesh_terms: D060387:Ascorbate Peroxidases; D003600:Cytosol / Q000737:chemistry / Q000201:enzymology*; D006861:Hydrogen Peroxide / Q000737:chemistry / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007501:Iron; D007700:Kinetics; D008665:Metalloporphyrins / Q000378:metabolism; D018532:Pisum sativum / Q000737:chemistry / Q000201:enzymology*; D010544:Peroxidases / Q000737:chemistry* / Q000378:metabolism; D013053:Spectrophotometry
chemical_list: D008665:Metalloporphyrins; D006861:Hydrogen Peroxide; D007501:Iron; D010544:Peroxidases; D060387:Ascorbate Peroxidases