Activation of serum prophenoloxidase in arthropod immunity. The specificity of cell wall glucan activation and activation by purified fungal glycoproteins of crayfish phenoloxidase

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Abstract
The activation of crayfish [Astacus astacus] serum prophenoloxidase by carbohydrates was specific for .beta.-1,3-glucans. Fractionation of the .beta.-1,3-glucan laminaran into laminaran M and laminaran G showed that both activated the proenzyme, but the G-chain had somewhat higher affinity for the proenzyme. Methylation analysis of these 2 fractions revealed that there were no 1,6-linkages present. Laminaripentaose, a linear pentasaccharide composed of (1 .fwdarw. 3)-linked .beta.-D-glucopyranosyl residues was also active but had a lower affinity for the proenzyme than laminaran G. Laminaran completely inhibited the activation of prophenoloxidase by the pentaose. In the concentrations tested, laminaran was not inhibitory to the phenoloxidase [EC 1.14.18.1] activity. Purified extracellular glycoproteins of the parasitic fungus Aphanomyces astaci also strongly activated crayfish serum prophenoloxidase. Only high MW glycoproteins were effective. Exo-.beta.-1,3-glucanase treatment decreased the activating capacity, suggesting that at least part of the glycoproteins consisted of .beta.-1,3-glucans. The significance of these results in the defense against parasitic fungi in crayfish is discussed.