Biely P, Vrsanská M, Krátký Z
Eur J Biochem. 1981 Oct;119(3):565-71. doi: 10.1111/j.1432-1033.1981.tb05645.x.
The action pattern and reaction mechanism of the endo-1,4-beta-xylanase of the yeast Cryptococcus albidus were investigated using reducing-end (1-3H)-labelled and uniformly 14C-labelled beta-1,4-xylooligosaccharides up to xylopentaose. The enzyme was found to catalyze degradation of oligosaccharides also by other pathways than a simple hydrolytic cleavage. Bond-cleavage frequency of xylotriose, xylotetraose and xylopentaose were found to be concentration dependent. At high substrate concentration reactions such as xylosyl, xylobiosyl and xylotriosyl transfer occur and result in the formation of products larger than the starting substrate. Xylose and xylobiose to significant extent enter the reaction pathways as glycosyl acceptors. None of the transglycosylic reactions observed with reducing-end-labelled substrates or acceptors were accompanied by a significant label redistribution from the reducing-end unit, suggesting that the enzyme-glycosyl intermediates effective in the transfer reactions can be formed from the non-reducing-end units of oligosaccharides. Evidence for the formation of a termomolecular shifted complex of beta-xylanase with xylotriose has also been obtained. All features of the degradation of oligosaccharides by beta-xylanase are consistent with the lysozyme-type reaction mechanism.
使用还原端（1-³H）标记和均匀¹⁴C标记的直至木五糖的β-1,4-木寡糖，研究了酵母浅白隐球酵母内切-1,4-β-木聚糖酶的作用模式和反应机制。发现该酶除了通过简单的水解裂解外，还通过其他途径催化寡糖的降解。发现木三糖、木四糖和木五糖的键裂解频率与浓度有关。在高底物浓度下，会发生木糖基、木二糖基和木三糖基转移等反应，并导致形成比起始底物更大的产物。木糖和木二糖在很大程度上作为糖基受体进入反应途径。用还原端标记的底物或受体观察到的转糖基反应均未伴随着还原端单元的显著标记重新分布，这表明在转移反应中有效的酶-糖基中间体可以由寡糖的非还原端单元形成。还获得了β-木聚糖酶与木三糖形成三分子移位复合物的证据。β-木聚糖酶对寡糖的降解的所有特征都与溶菌酶型反应机制一致。
