A two-substrate kinetic study of peroxidase cationic isoenzymes in barley malt

Abstract

Ten active cationic peroxidase isoenzymes were identified by polyacrylamide gel electrophoresis of extracts from malt of Triumph barley. These were partially separated on CM-Sepharose CL-6B and their properties examined. The five active peaks had different pH optima for the oxidation of 2,2′-azinobis(3-ethylbenzthiazoline 6-sulphonate) (ABTS), ranging from pH 3.25 to 3.73, and different inactivation rates at 55°, two being significantly more stable than the rest. A two-substrate kinetic study revealed a parallel pattern of double reciprocal plots for some of the active peaks, a converging pattern for others and a range of true K m values for the isoenzyme peaks varying from 76 to 710, μM for hydrogen peroxide and 2–310, μM for ABTS. The significance of the observations is discussed in relation to the known activity of peroxidase during brewery mashing.