Enzymatic degradation of methacrylated dextrans
Enzymatic degradation of methacrylated dextrans
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DOI：
10.1021/ma970887s
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发表时间：
1997-12-01
期刊：
影响因子：
5.5
通讯作者：
Hennink, WE
中科院分区：
文献类型：
--
作者：
Franssen, O;vanOoijen, RD;Hennink, WE
利用葡聚糖酶对右旋糖酐和甲基丙烯酸葡聚糖（dex-MA）进行降解，并采用电喷雾质谱对降解产物进行表征。结果表明，右旋糖酐和dex-MA的主要降解产物均为异麦芽糖。在降解的dex-MA中，主要的甲基丙烯酸酯化产物是异麦芽三糖。具有较高分子量的低聚糖（高达异麦芽六糖）和多甲基丙烯酸酯化低聚糖的相对贡献随着dex-MA取代度的增加而增加。三底物模型的酶动力学表明，单甲基丙烯酸酯化底物的米氏常数小于未取代的底物，而多甲基丙烯酸酯化底物的米氏常数较高。这表明一个甲基丙烯酸酯基团与酶中疏水结合亚位点的有利相互作用。然而，最大降解速率，是实质上低于取代基板比原生基板。从这些结果。可以得出结论，该酶水解在dex-MA链中甲基丙烯酸化的吡喃葡萄糖残基和未取代的吡喃葡萄糖残基之间的糖苷键。这一假设得到了电喷雾质谱法的进一步支持，因为在寡糖的非还原端存在碎片化形成的离子，并且不存在甲基丙烯酸酯数量等于或超过吡喃葡萄糖残基数量的寡糖。
Dextran and methacrylated dextrans (dex-MA) were degraded with dextranase, and the formed degradation products were characterized by electrospray mass spectrometry. It was shown that the main degradation product was isomaltose for both dextran and dex-MA. In degraded dex-MA, the main methacrylated product was isomaltotriose. The relative contribution of oligosaccharides with a higher molecular weight (up to isomaltohexaose) and of multiply methacrylated oligosaccharides increased with the degree of substitution of dex-MA. Enzyme kinetics with a three-substrate model showed that the Michaelis-Menten constant for the monomethacrylated substrate was smaller than for the unsubstituted substrate, whereas the Michaelis-Menten constant for multiply methacrylated susbtrates was higher. This indicates a favorable interaction of one methacrylate group with a hydrophobic binding subsite in the enzyme. The maximum degradation rate, however, was substantially lower for the substituted substrates than for the native substrate. From these results. it is concluded that the enzyme hydrolyzes a glycosidic bond between a methacrylated glucopyranose residue and an unsubstituted one in the dex-MA chain. This hypothesis is further supported with electrospray mass spectrometry because of both the presence of an ion formed by fragmentation at the nonreducing end of an oligosaccharide and the absence of oligosaccharides in which the number of methacrylates equals or exceeds the number of glucopyranose residues.