Organic Department, The Radiochemical Centre, Amersham, Buckinghamshire, England.
Plant Physiol. 1970 Sep;46(3):406-11. doi: 10.1104/pp.46.3.406.
Adenosine diphosphoglucose and uridine diphosphoglucose pyrophosphorylase activities (class EC 2.7.7.9) were assayed radiochemically in ammonium sulfate fractions prepared from mature and germinating wheat grain. Both enzymes showed similar pH optima and metal ion requirements but differed markedly in their response to activation by d-glycerate 3-phosphate and inhibition by sulfate and phosphate.Their stability characteristics also differed greatly. While UDP-glucose pyrophosphorylase was very stable, ADP-glucose pyrophosphorylase rapidly lost activity in dilute solution and upon desalting on columns of Sephadex and was only partially stabilized when stored as a suspension in ammonium sulfate. Relatively high salt concentrations were required to maintain even short term stability. ADP-glucose and UDP-glucose pyrophosphorylases had apparent K(m) values for alpha-d-glucose 1-phosphate of 4.4 x 10(-5)m and 10(-3)m, respectively. In extracts from dry grain, the number of units of UDP-glucose pyrophosphorylase were about 30-fold greater than the number of units of ADP-glucose pyrophosphorylase. During germination, the activity of UDP-glucose pyrophosphorylase increased markedly in both the embryo and the endosperm, while ADP-glucose pyrophosphorylase fell slightly over the initial 4 days of germination.
在从成熟和萌发的小麦籽粒中制备的硫酸铵级分中，用放射化学法测定了腺苷二磷酸葡萄糖和尿苷二磷酸葡萄糖焦磷酸化酶活性（EC 2.7.7.9 类）。两种酶都表现出相似的 pH 最佳值和金属离子要求，但对 3-磷酸甘油酸的激活和硫酸盐和磷酸盐的抑制反应明显不同。它们的稳定性特征也有很大差异。虽然 UDP-葡萄糖焦磷酸化酶非常稳定，但 ADP-葡萄糖焦磷酸化酶在稀溶液中迅速失活，在 Sephadex 柱上脱盐时活性迅速下降，仅在作为硫酸铵悬浮液储存时部分稳定。即使是短期稳定也需要相对高的盐浓度。ADP-葡萄糖和 UDP-葡萄糖焦磷酸化酶对α-D-葡萄糖 1-磷酸的表观 K(m)值分别为 4.4 x 10(-5)m 和 10(-3)m。在干谷物提取物中，UDP-葡萄糖焦磷酸化酶的单位数约为 ADP-葡萄糖焦磷酸化酶的 30 倍。在萌发过程中，胚和胚乳中 UDP-葡萄糖焦磷酸化酶的活性都明显增加，而 ADP-葡萄糖焦磷酸化酶在萌发的最初 4 天内略有下降。
