School of Pharmacy, University of East Anglia, Norwich, UK.
Carbohydr Res. 2010 Feb 26;345(4):487-97. doi: 10.1016/j.carres.2009.12.019. Epub 2009 Dec 28.
Individual pectin polymers and complexes, isolated from the pericarp of unripe tomato (Lycopersicon esculentum var. Rutgers), were subjected to a mild acid hydrolysis and visualised and characterised by atomic force microscopy (AFM). The AFM images confirm earlier studies showing that individual pectic polysaccharides often possess long branches. The AFM data have been used to construct size and molecular weight distributions for the single molecules and complexes, from which the calculated number-average and weight-average molecular weights can then be compared directly with the published literature data on the rheology of bulk samples. Loss of the neutral sugars arabinose, galactose and rhamnose from the pectin samples does not significantly alter either the size or the branching density of the individual polymers, but is reflected in a breakdown of the complexes. Significant loss of galacturonic acid at long hydrolysis times was found to be accompanied by changes in the size and branching of the single polymers and further breakdown of the complexes. The results suggest that rhamnose, arabinose and galactose are not the major components of the individual polymers but are, instead, confined to the complexes. The polysaccharides represent a previously unrecognised branched homogalacturonan with a minimum mean size some three times larger than that previously reported. The complexes consist of homogalacturonans (HGs) held together by rhamnogalacturonan I (RG-I) regions. Comparison of the rate of depolymerisation of the homogalacturonans and complexes with the published data on changes in the intrinsic viscosity of bulk pectin samples, subjected to similar acid hydrolysis, suggests that the different rates of depolymerisation of RG-I and HG contribute separately to the observed changes in intrinsic viscosity during acid hydrolysis. Thus data obtained using a single molecule microscopy technique provides new insights into the behaviour in the bulk.
个体果胶聚合物和复合物，从未成熟的番茄（Lycopersicon esculentum var. Rutgers）的果皮中分离出来，经过温和的酸水解，并通过原子力显微镜（AFM）进行可视化和特征分析。AFM 图像证实了早期的研究表明，个体果胶多糖通常具有长支链。AFM 数据已用于构建单个分子和复合物的大小和分子量分布，从中可以直接计算出数均分子量和重均分子量，并与关于大块样品流变学的已发表文献数据进行比较。果胶样品中中性糖阿拉伯糖、半乳糖和鼠李糖的损失不会显著改变单个聚合物的大小或支化密度，但会反映在复合物的分解中。在长时间水解时，发现半乳糖醛酸的大量损失伴随着单个聚合物的大小和支化的变化以及复合物的进一步分解。结果表明，鼠李糖、阿拉伯糖和半乳糖不是单个聚合物的主要成分，而是局限于复合物。这些多糖代表了以前未被识别的支化同半乳糖醛酸聚糖，其平均大小至少比以前报道的大 3 倍。复合物由通过鼠李半乳糖醛酸 I（RG-I）区域结合在一起的同半乳糖醛酸聚糖（HG）组成。将同半乳糖醛酸聚糖和复合物的解聚速率与关于在类似酸水解条件下大块果胶样品的特性粘度变化的已发表数据进行比较表明，RG-I 和 HG 的不同解聚速率分别有助于观察到的酸水解过程中特性粘度的变化。因此，使用单分子显微镜技术获得的数据提供了对整体行为的新见解。
