In vivo Peroxidase Inhibitor in Bush Bean (Phaseolus vulgaris)Leaves

RECENT reports from this laboratory described a peroxidase enzyme from bush bean roots which catalysed the oxidative decarboxylation of oxaloacetate (OAA) to malonate1–3. Attempts to demonstrate this enzyme in crude extracts of bush bean leaves were unsuccessful. Using standard enzyme purification procedures, however, one of us (J. Y. L.) purified a peroxidase enzyme from bush bean leaves 240-fold and showed that the purified enzyme was indeed able to convert OAA to malonate, confirming the presence of the peroxidase enzyme in bush bean leaves. Subsequent studies showed that the crude enzyme preparation from bean leaves contained an inhibitor of peroxidase catalysed reactions. Inhibitors of peroxidase catalysed reactions have also been identified in pea epicotyl4, pineapple stem tissue5, and cotton leaf tissue6; but the extent to which these inhibitors exert their effect in vivo has not been determined. This communication presents evidence indicating that the peroxidase inhibitor in bush bean leaves inhibited the in vivo peroxidase catalysed conversion of OAA to malonate.