Lerouge P, O'Neill M A, Darvill A G, Albersheim P
Complex Carbohydrate Research Center, University of Georgia, Athens 30602-4712.
Carbohydr Res. 1993 May 7;243(2):359-71. doi: 10.1016/0008-6215(93)87039-u.
Rhamnogalacturonan I (RG-I) has been isolated from the walls of suspension-cultured sycamore cells (Acer pseudoplatanus), and additional structural features of the polysaccharide were elucidated. Treatment of RG-I with a purified endo-(1-->5)-alpha-L-arabinanase released a series of arabinose-containing oligosaccharides with degrees of polymerization (dp's) between 2 and 20. These oligosaccharides were shown, by glycosyl-linkage composition analysis, to contain terminal, 5-, and (3-->5)-linked Araf residues. These results provide evidence that a branched arabinan is attached to the backbone of RG-I. RG-I was freed of 95% of its arabinosyl residues by treating the polysaccharide with a combination of endo-(1-->5)-alpha-L-arabinanase and alpha-L-arabinosidase. No galacturonic acid was released by these enzymes, which is evidence that the arabinosyl-containing portions of the side chains do not contain galactosyluronic acid residues. The galactose-containing portions of the side chains of RG-I were not fragmented by an endo-(1-->4)-beta-D-galactanase. However, approximately 85% of the galactose and small amounts of galacturonic acid were released by digestion of arabinose-depleted RG-I with a combination of endo- and exo-beta-D-galactanases. The galacturonic acid may have been released by small amounts of an exo-alpha-galactosyluronidase contaminating the galactanases. Treatment of RG-I with this mixture of endo- and exo-glycanases resulted in a relatively size-homogeneous, almost side chain-free backbone composed of the O-acetylated diglycosyl repeating unit -->4)-alpha-D-GalpA-(1-->2)-alpha-L-Rhap. A combination of 1H NMR spectroscopy and periodate oxidation established that the backbone repeating unit contained a single O-acetyl substituent on C-2 or C-3 of each galactosyluronic acid residue.
鼠李半乳糖醛酸聚糖I（RG-I）已从悬浮培养的悬铃木细胞（槭树）壁中分离出来，并且阐明了该多糖的其他结构特征。用纯化的内切（1→5）-α-L-阿拉伯聚糖酶处理RG-I，释放出一系列聚合度（dp）在2至20之间的含阿拉伯糖的寡糖。通过糖基连接组成分析表明，这些寡糖含有末端、5-和（3→5）连接的阿拉伯糖残基。这些结果提供了证据，表明分支的阿拉伯聚糖连接到RG-I的主链上。通过用内切（1→5）-α-L-阿拉伯聚糖酶和α-L-阿拉伯糖苷酶的组合处理该多糖，RG-I的95%阿拉伯糖基残基被去除。这些酶没有释放出半乳糖醛酸，这证明侧链的含阿拉伯糖部分不含有半乳糖醛酸残基。RG-I侧链的含半乳糖部分没有被内切（1→4）-β-D-半乳聚糖酶切割。然而，用内切和外切β-D-半乳聚糖酶组合消化去除阿拉伯糖的RG-I，大约85%的半乳糖和少量半乳糖醛酸被释放出来。半乳糖醛酸可能是由污染半乳聚糖酶的少量外切α-半乳糖基醛酸酶释放出来的。用这种内切和外切聚糖酶混合物处理RG-I，产生了一种相对大小均匀、几乎无侧链的主链，其由O-乙酰化二糖基重复单元→4）-α-D-半乳糖醛酸-（1→2）-α-L-鼠李糖组成。1H NMR光谱和高碘酸盐氧化的组合确定，主链重复单元在每个半乳糖醛酸残基的C-2或C-3上含有单个O-乙酰基取代基。
