Induction of an anionic peroxidase in cowpea leaves by exogenous salicylic acid

Two isoperoxidases were detected in cowpea (Vigna unguiculato) leaves. Treatment of the primary leaves with 10 mM saticylic acid increased the total peroxidase activity contributed by the anionic isoform. To isolate both the anionic and cationic peroxidases the leaf crude extract was loaded on a Superose 12 HR 10/30 column followed by chromatography on Mono-Q HR 5/5. Both enzymes were stable in a pH range from 5 to 7. The optimum-temperatures for the cationic and anionic peroxidase isoforms were, respectively, 20-30 degrees C and 30 degrees C. The dependence of guaiacol. oxidation rate varying its concentration at constant H2O2 concentration showed, for both enzymes, Michaetis-Menten-type kinetic. Apparent Km, were 0.8 and 4.8 mu M for the cationic and anionic isoperoxidases, respectively. (c) 2005 Elsevier GmbH. All rights reserved.