Phenoloxidase and its zymogen from the haemolymph of larvae of the lepidopteran Spodoptera littoralis (Lepidoptera: Noctuidae)
1995
Lee, M.J. | Anstee, J.H.
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 Km 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 micromolar) and kojic acid (50% inhibition at 135 micromolar, inhibition constant of 69 micromolar).
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