β-（1→3）葡聚糖合成酶的底物激活及其对从小麦叶鞘颗粒酶和 UDP-D-葡萄糖获得的β-葡聚糖结构的影响。
Substrate Activation of beta-(1 --> 3) Glucan Synthetase and Its Effect on the Structure of beta-Glucan Obtained from UDP-d-glucose and Particulate Enzyme of Oat Coleoptiles.
机构信息
Department of Biochemistry, University of California, Berkeley, California 94720.
出版信息
Plant Physiol. 1973 Jun;51(6):998-1001. doi: 10.1104/pp.51.6.998.
UDP-d-glucose, at a micromolar level in the presence of MgCl(2) and oat (Avena sativa) coleoptile particulate enzyme which contains both beta-(1 --> 3) and beta-(1 --> 4) glucan synthetases, produces glucan with mainly beta-(1 --> 4) glucosyl linkages. An activation of beta-(1 --> 3) glucan synthetase by UDP-d-glucose and a decrease in the formation of beta-(1 --> 3) glucan in the presence of MgCl(2) have been observed. However, at high substrate concentration (>/= 10(-4)m), the activation of beta-(1 --> 3) glucan synthetase is so pronounced that the formation of beta-(1 --> 3) glucosyl linkage predominates in synthesized glucan regardless of the presence of MgCl(2). These observations may explain the striking shift in the composition of glucan of particulate enzyme from a beta-(1 --> 4) to beta-(1 --> 3) glucosyl linkage when UDP-d-glucose concentration is raised from a low concentration (</= 10(-5)m) to a higher concentration (>/= 10(-4)m).Besides UDP-d-glucose, CDP-d-glucose can also serve as substrate for the formation of beta-(1 --> 3) glucan in the presence of beta-(1 --> 3) synthetase.
在含有 MgCl2 和燕麦（Avena sativa） coleoptile 颗粒酶的微摩尔水平的 UDP-d-葡萄糖存在下，该酶同时含有β-（1--->3）和β-（1--->4）葡聚糖合成酶，可产生主要具有β-（1--->4）葡萄糖苷键的葡聚糖。已经观察到 UDP-d-葡萄糖对β-（1--->3）葡聚糖合成酶的激活以及 MgCl2 存在下β-（1--->3）葡聚糖形成的减少。然而，在高底物浓度（>= 10-4m）下，β-（1--->3）葡聚糖合成酶的激活非常明显，以至于无论是否存在 MgCl2，合成的葡聚糖中β-（1--->3）葡萄糖苷键的形成都占主导地位。这些观察结果可以解释当 UDP-d-葡萄糖浓度从低浓度（<= 10-5m）升高至高浓度（>= 10-4m）时，颗粒酶中葡聚糖的组成从β-（1--->4）到β-（1--->3）葡聚糖糖苷键的惊人转变。除了 UDP-d-葡萄糖外，CDP-d-葡萄糖也可以在β-（1--->3）合成酶存在的情况下作为β-（1--->3）葡聚糖形成的底物。
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