Activation of pro-phenoloxidase by bacterial cell walls or beta-1,3-glucans in plasma of the silkworm, Bombyx mori.

Silkworm hemolymph plasma contains pro-phenoloxidase and the activating system for the pro-enzyme. The latter was triggered by elicitors such as Gram-negative or Gram-positive bacterial cell wall, glucans with beta-1,3-glycosidic linkages and denatured lipophorin, which is one of silkworm plasma proteins, but not by lipopolysaccharide, dextram 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.