大豆根瘤中的蔗糖合酶。
Sucrose synthase of soybean nodules.
作者信息
Morell M, Copeland L
机构信息
Department of Agricultural Chemistry, University of Sydney, New South Wales 2006, Australia.
出版信息
Plant Physiol. 1985 May;78(1):149-54. doi: 10.1104/pp.78.1.149.
SUCROSE SYNTHASE (UDPGLUCOSE: d-fructose 2-alpha-d-glucosyl transferase, EC 2.4.1.13) has been purified from the plant cytosolic fraction of soybean (Glycine max L. Merr cv Williams) nodules. The native enzyme had a molecular weight of 400,000. The subunit molecular weight was 90,000 and a tetrameric structure is proposed for soybean nodule sucrose synthase. Optimum activity in the sucrose cleavage and synthesis directions was at pH 6 and pH 9.5 respectively, and the enzyme displayed typical Michaelis-Menten kinetics. Soybean nodule sucrose synthase had a high affinity for UDP (K(m), 5 micromolar) and a relatively low affinity for ADP (apparent K(m), 0.13 millimolar) and CDP (apparent K(m), 1.1 millimolar). The K(m) for sucrose was 31 millimolar. In the synthesis direction, UDPglucose (K(m), 0.012 millimolar) was a more effective glucosyl donor than ADPglucose (K(m), 1.6 millimolar) and the K(m) for fructose was 3.7 millimolar. Divalent cations stimulated activity in both the cleavage and synthesis directions and the enzyme was very sensitive to inhibition by heavy metals.
蔗糖合酶（UDP葡萄糖：d-果糖2-α-d-葡萄糖基转移酶，EC 2.4.1.13）已从大豆（Glycine max L. Merr cv Williams）根瘤的植物胞质部分中纯化出来。天然酶的分子量为400,000。亚基分子量为90,000，推测大豆根瘤蔗糖合酶具有四聚体结构。蔗糖裂解和合成方向的最佳活性分别在pH 6和pH 9.5，并且该酶表现出典型的米氏动力学。大豆根瘤蔗糖合酶对UDP具有高亲和力（K(m)，5微摩尔），对ADP（表观K(m)，0.13毫摩尔）和CDP（表观K(m)，1.1毫摩尔）具有相对低的亲和力。蔗糖的K(m)为31毫摩尔。在合成方向上，UDP葡萄糖（K(m)，0.012毫摩尔）是比ADP葡萄糖（K(m)，1.6毫摩尔）更有效的葡萄糖基供体，果糖的K(m)为3.7毫摩尔。二价阳离子在裂解和合成方向上均刺激活性，并且该酶对重金属抑制非常敏感。
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