Peroxidase Isozymes from Horseradish Roots

This report describes the catalytic properties of seven homogeneous peroxidase isozymes. The catalytic properties of each isozyme were determined in a peroxidatic reaction with the use of o-dianisidine as the substrate, and in an oxidatic reaction with the use of oxalacetate as the substrate. Each isozyme was capable of catalyzing the oxidation of both substrates and they exhibited identical cofactor requirements. The time course for each isozyme was identical except for Isozyme A-3, which was inactivated rapidly in the peroxidatic reaction. Isozymes A-1, A-2, and A-3 possessed similar catalytic properties and were classified into one group. The remaining isozymes, B, C, D, and E, also possessed similar catalytic properties and were classified into another group. The two groups of isozymes, however, showed marked differences in pH optima, specific activities, apparent Km values, and affinity toward inhibitors.