Chemical structure and chain conformation of the water-insoluble glucan isolated fromPleurotus tuber-regium

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Abstract
A water‐insoluble polysaccharide (TM8) was isolated from sclerotium of Pleurotus tuber‐regium by extraction with 0.5M NaOH aqueous solutions at 120°C. Its chemical structure was confirmed by infrared, high performance liquid chromatography, gas chromatography, and 13C NMR in dimethylsulfoxide (DMSO) to be composed of β‐(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°C. The dependencies of intrinsic viscosity [η] and radius of gyration 〈s2〉z1/2 on weight‐average molecular mass Mw for this glucan were found to be [η] = (9.24 ± 0.2) × 10−2Mw0.51 ± 0.02 (cm3g−1) and 〈s2〉z1/2 = (3.67 ± 0.3) × 10−2Mw0.56 ± 0.02 (nm) in the range of Mw from 1.07 × 104 to 77.4 × 104. Based on current theories for a wormlike chain, the conformational parameters of the glucan TM8 were found to be 408 (nm−1) for ML, 3.1 (nm) for q, and 16.8 for C∞, suggesting that the polysaccharide exists as a dense random‐coil chain in DMSO, due to branched structure. © 2001 John Wiley & Sons, Inc. Biopolymers 59: 457–464, 2001

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