Ma Zhaocheng, Wang Jianguo, Zhang Lina
Department of Chemistry, Wuhan University, Wuhan 430072, China.
Biopolymers. 2008 Jul;89(7):614-22. doi: 10.1002/bip.20971.
From Auricularia auricula-judae, a water soluble beta-D-glucan, named as AAG, was isolated by extraction with 70% ethanol/water solution. Its chemical structure was analyzed by gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS), matrix-assisted laser desorption /ionization (MALDI)-time of flight (TOF), and 1D, 2D NMR. AAG was detected, for the first time, to be composed of a main chain of (1-->4)-linked D-glucopyranosyl with glucopyranosyl side groups at O6. With the help of MALDI-TOF-MS, the sequence and the distribution of glucuronic acid were determined and the content of glucuronic acid is about 19%. Five fractions were prepared from the AAG sample in water by ultrasonic degradation method. Their molecular weight, size, and shape (chain conformation) were studied by dynamics light scattering (DLS), static laser light scattering (LLS), size exclusion chromatography combined LLS (SEC-LLS) and viscometry in 0.1M NaCl aqueous solution at 25 degrees C. The dependence of intrinsic viscosity ([eta]) on Mw for this polysaccharide was established to be [eta] = 1.22 x10(-3)Mw (1.00) (cm3 g(-1)) in the range of Mw from 3.40 x 10(4) to 2.88 x 10(5). The conformational parameters of the AAG polysaccharide were found to be 820 nm(-1) for molar mass per unit contour length (ML), 12.3 nm for persistence length (q) and 2.1 for rho (s2(1/2)/Rh). The results suggested that the polysaccharide exists as extended chains in 0.1M NaCl aqueous solution. The chemical structure of AAG containing glucuronic acid and side groups led to steric hindrance, resulting in the increased stiffness of the chains.
从木耳中，通过用70%乙醇/水溶液萃取分离出一种名为AAG的水溶性β-D-葡聚糖。采用气相色谱（GC）、气相色谱-质谱联用（GC-MS）、基质辅助激光解吸/电离（MALDI）-飞行时间（TOF）以及一维、二维核磁共振对其化学结构进行了分析。首次检测到AAG由一条（1→4）连接的D-吡喃葡萄糖主链和O6位的吡喃葡萄糖侧基组成。借助MALDI-TOF-MS确定了葡萄糖醛酸的序列和分布，葡萄糖醛酸含量约为19%。通过超声降解法从水中的AAG样品中制备了五个级分。在25℃下，于0.1M NaCl水溶液中，采用动态光散射（DLS）、静态激光光散射（LLS）、尺寸排阻色谱联用LLS（SEC-LLS）和粘度测定法研究了它们的分子量、尺寸和形状（链构象）。确定了该多糖的特性粘度（[η]）与Mw的关系为[η] = 1.22×10⁻³Mw¹.⁰⁰（cm³ g⁻¹），Mw范围为3.40×10⁴至2.88×10⁵。发现AAG多糖的构象参数为单位轮廓长度的摩尔质量（ML）为820 nm⁻¹，持久长度（q）为12.3 nm，rho（s₂¹/₂/Rh）为2.1。结果表明该多糖在0.1M NaCl水溶液中以伸展链的形式存在。含有葡萄糖醛酸和侧基的AAG的化学结构导致空间位阻，从而使链的刚性增加。
