Chemical structure and chain conformation of the water-insoluble glucan isolated from Pleurotus tuber-regium.

A water-insoluble polysaccharide (TM8) was isolated from sclerotium of Pleurotus tuber-regium by extraction with 0.5M NaOH aqueous solutions at 120 degrees C. Its chemical structure was confirmed by infrared, high performance liquid chromatography, gas chromatography, and (13)C NMR in dimethylsulfoxide (DMSO) to be composed of beta-(1 --> 3)-D-glucan backbone chain linked with a branched glucose, one out of every three glycosyl units being substituted at C6 position. The glucan TM8 in DMSO was fractionated by nonsolvent addition method into ten fractions, and the solution properties were studied by size exclusion chromatography combined with multiangle laser light scattering (SEC-MALLS) and viscometry in DMSO at 30 degrees C. The dependencies of intrinsic viscosity [eta] and radius of gyration [(s(2)(1/2)(z-2)] on weight-average molecular mass M(w) for this glucan were found to be [eta] = (9.24 +/- 0.2) x 10(-2)M(w)(0.51 +/- 0.02) (cm(3)g(-1)) and [(s(2)(1/2)(z-2)] = (3.67 +/- 0.3) x 10(-2)M(w)(0.56 +/- 0.02) (nm) in the range of M(w) from 1.07 x 10(4) to 77.4 x 10(4). Based on current theories for a wormlike chain, the conformational parameters of the glucan TM8 were found to be 408 (nm(-1)) for M(L), 3.1 (nm) for q, and 16.8 for C(infinity), suggesting that the polysaccharide exists as a dense random-coil chain in DMSO, due to branched structure. Copyright 2001 John Wiley & Sons, Inc.