ACTIVATION OF LIMULUS COAGULATION FACTOR-G BY SEVERAL (1-]3)-BETA-D-GLUCANS - COMPARISON OF THE POTENCY OF GLUCANS WITH IDENTICAL DEGREE OFPOLYMERIZATION BUT DIFFERENT CONFORMATIONS

It has been demonstrated that both linear and branched (6-O-beta-D-glu cosyl) (1 --> 3)-beta-D-glucans taking a single helical conformation a re more effective than those taking a triple helical conformation for the activation of factor G from horseshoe crab amebocytes, as revealed by high-resolution solid-state C-13-NMR spectroscopy [Saito, H. et al . (1991) Carbohydr. Res. 217,181-190]. Annealing the linear glucan at 180-degrees-C was essential to convert the conformation from the singl e helix to the triple helix. We found that heating of the glucan at su ch a high temperature resulted in depolymerization of the sample to mo lecular weight smaller than 10,000, which may influence the conformati on and the above-mentioned biological activity. To eliminate ambiguity arising from the depolymerization of the glucan during annealing, we aimed to relate the biological activity to the conformation of samples whose chain lengths are identical, because the potency is known to de pend on the molecular weight of the glucans. This molecular weight dep endency of the potency, however, was found to be not the dominant fact or, provided that the molecular weight is large enough to allow format ion of the single helix conformation. Therefore, the single helical co nformation of (1 --> 3)-beta-D-glucans is clearly demonstrated to be t he dominant contributor to the activation of limulus coagulation facto r G.