ACTIVATION OF A LIMULUS COAGULATION FACTOR-G BY (1-]3)-BETA-D-GLUCANS

Various oligo- and poly-saccharides differing in sugar compositions and types of linkage were examined for their ability to activate a limulus coagulation factor G, the first protease in an alternative coagulation cascade of the horseshoe crab, Tachypleus tridentatus, whose amebocytes have originally been known to contain a lipopolysaccharide(LPS)-driven pathway leading to the formation of coagulin gel. Linear and branched (1 --> 3)-beta-D-glucans and mixed linkage (1 --> 3), (1 --> 4)-beta-D-glucans were found to exhibit the ability to activate factor G at concentrations of 10(-8)-10(-10) g/mL as assayed by amidolytic activity of the clotting enzyme. Laminaran oligosaccharides, laminaran dextrins (number-average mol. wt. less-than-or-equal-to 5800), and other polysaccharides including carboxymethylcellulose, amylose, starch, D-fructans, alpha-L-arabinan. beta-D-xylans, (1 --> 3)-beta-D-galactan, water-soluble chitin derivatives, chondroitin, chondroitin sulfates, hyaluronan, keratan sulfate, heparins, heparan sulfate, and LPS's were virtually inactive as activators even at a concentration of 10(-7) g mL. The activating ability increased with increasing number-average mol. wt. (6800-216000) of linear (1 --> 3)-beta-D-glucans. The apparent activating ability of gyrophoran, nigeran, and yeast alpha-D-mannan was largely abolished by digestion with a highly purified Arthrobacter luteus endo-(1 --> 3)-beta-D-glucanase, which provided supportive evidence for the activation to be ascribed to contaminating (1 --> 3)-beta-D-glucan(s). Possible participation of ordered structures of ( --> 3)-beta-D-glucans in the activation of factor G is discussed.