Sulová Z, Farkas V
Institute of Chemistry, Slovak Academy of Sciences, Bratislava, Slovakia.
Gen Physiol Biophys. 1998 Jun;17(2):133-42.
Xyloglucan-endotransglycosylase (XET) is an enzyme involved in the metabolism of xyloglucan (XG) in plant cell walls and seeds. This enzyme acts both as a hydrolase and as a transglycosylase by transferring the fragments of xyloglucan molecules to other XG molecules or xyloglucan-derived oligosaccharides (XGOs). In this work, we studied the kinetics of interaction between XET and XG. The equilibrium in the reaction of XG degradation by XET was found to depend on the initial enzyme concentration and the availability of suitable glycosyl acceptors. After reaching the equilibrium, the addition to the reaction mixture of XET or XGOs caused further degradation of XG, and a new equilibrium with a higher degree of XG depolymerization was established. These results indicated that in the course of XG depolymerization, the enzyme is bound in a relatively stable, temporarily inactive enzyme-glycosyl complex and this complex is decomposed by transferring its glycosyl moiety to suitable oligosaccharide acceptor. Mouse polyclonal antibody against XET linked to AffiGel 10 (Affi-Ab) adsorbed both XET and XET-XG complex but not [3H]XG alone. XET immobilized onto Affi-Ab was able to bind [3H]XG and catalyze transglycosylation in presence of XGOs.
木葡聚糖内转糖基酶（XET）是一种参与植物细胞壁和种子中木葡聚糖（XG）代谢的酶。这种酶既作为水解酶，又作为转糖基酶，通过将木葡聚糖分子片段转移到其他XG分子或木葡聚糖衍生的寡糖（XGOs）上发挥作用。在这项工作中，我们研究了XET与XG之间相互作用的动力学。发现XET降解XG反应中的平衡取决于初始酶浓度和合适糖基受体的可用性。达到平衡后，向反应混合物中添加XET或XGOs会导致XG进一步降解，并建立一个具有更高XG解聚程度的新平衡。这些结果表明，在XG解聚过程中，酶与相对稳定的、暂时无活性的酶 - 糖基复合物结合，并且该复合物通过将其糖基部分转移到合适的寡糖受体上而分解。与AffiGel 10偶联的抗XET小鼠多克隆抗体（Affi - Ab）能吸附XET和XET - XG复合物，但不能单独吸附[3H]XG。固定在Affi - Ab上的XET能够结合[3H]XG并在XGOs存在下催化转糖基化反应。
