PHENOLOXIDASE AND ITS ZYMOGEN FROM THE HEMOLYMPH OF LARVAE OF THE LEPIDOPTERAN SPODOPTERA-LITTORALIS (LEPIDOPTERA, NOCTUIDAE)

Haemolymph serum phenoloxidase from larvae of the noctuid moth Spodoptera littoralis is present as an inactive proenzyme, prophenoloxidase. Partially purified serum prophenoloxidase was activated by methanol, but not by laminarin, lipopolysaccharides, bovine trypsin or chymotrypsin. Phenoloxidase activity was optimal between pH 7.0 and 7.5 for the oxidation of L-DOPA, with an apparent K-m of 1.35 mM for this substrate. Both Mg2+ and Ca2+ stimulated phenoloxidase activity compared with controls and maximal stimulation was observed at about 30 mM for both ions. EDTA had little effect on activity even at high concentrations. Phenoloxidase activity was inhibited by dithiothreitol (50% inhibition at 20 mu M) and kojic acid (50% inhibition at 135 mu M, inhibition constant of 69 mu M).