KINETIC AND SPECTRAL PROPERTIES OF PEA CYTOSOLIC ASCORBATE PEROXIDASE

Sufficient highly purified native pea cytosolic ascorbate peroxidase w as obtained to characterize some of its kinetic and spectral propertie s, Its rate constant for compound I formation from reaction with H2O2 is 4.0 x 10(7) M(-1) s(-1), somewhat faster than is typical for peroxi dases, Compound I has the typical optical spectrum of an iron(IV)-porp hyrin-pi-cation radical, despite considerable homology with yeast cyto chrome c peroxidase. The rate constant for compound I reduction by asc orbate 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 prof ile for compound I formation indicates a pK(a) value of 5.0 for a grou p affecting the active site reaction.