Activation of pro-phenoloxidase by bacterial cell walls or β-1,3-glucans in plasma of the silkworm, [formula omitted

Abstract

Silkworm hemolymph plasma contains pro-phenoloxidase ∗ ∗ Abbreviations : PO, phenoloxidase, o -di-phenol: O 2 oxidoreductase (EC 1.10.3.1); pro-PO, pro-phenoloxidase; hPPAE, hemolymph pro-phenoloxidase activating enzyme; p-NPGB, p -nitrophenyl- p ′-guanidinobenzoate; dopa, 3,4-dihydroxyl-L-phenylalanine; DFP, di-isopropylphosphrofluoridate; T-M buffer, 0.01 M Tris-maleate buffer, pH 6.5, containing 0.15 M NaCl; CS-plasma, plasma fraction of silkworm hemolymph (see Materials and Methods). and the activating system for the pro-enzyme. The latter was triggered by elicitors such as Gramnegative or Gram-positive bacterial cell wall, glucans with β-1,3-glycosidic linkages and denatured lipophorin, which is one of silkworm plasma proteins, but not by lipopolysaccharide, dextran sulfate, kaolin or inulin. Calcium was required for the elicitors to activate the system. However, putative pro-PO activating enzyme, which activity is induced in plasma by the action of the elicitors, could activate pro-PO in the absence of the ion, suggesting that at least two reaction steps are involved in the activation reaction of pro-PO in plasma. The activating enzyme was completely inhibited in the presence of p-NPGB, an inhibitor for serine protease.