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首页> 外文期刊>European Journal of Medicinal Chemistry: Chimie Therapeutique >Sucrose synthase isoforms in cultured tobacco cells
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Sucrose synthase isoforms in cultured tobacco cells

机译：培养烟草细胞中的蔗糖合酶同工型

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摘要

The plant enzyme sucrose synthase (SuSy; EC 2.4.1.13) catalyzes the reversible conversion of sucrose and UDP into UDP-glucose (UDP-Glc) and fructose. The enzyme exists in different isoforms and is both located in the cytosol, membrane-bound and associated to the actin cytoskeleton. We here investigate sucrose synthase from tobacco (Nicotiana tabacum L.) BY-2 heterotrophic cell suspensions. Two different isoforms of sucrose synthase SuSy1 and SuSy2, could be purified from cytosolic extracts of these cells using a combination of poly(ethylene glycol) (PEG) precipitation, gel filtration, ion-exchange chromatography and affinity chromatography. They were clearly distinct, both with regard to the binding to the ion-exchange column and with regard to their kinetic and regulatory properties. SuSy1, the more abundant species, showed lower V_(max) and K_m for sucrose and UDP compared to the less abundant SuSy2. The activity of SuSy2 in the breakdown direction was stimulated by 60% by actin, in contrast to that of SuSy1, which showed a 17% inhibition. An indication of interaction between SuSy1 and actin was obtained by partitioning in aqueous Dextran–PEG two-phase systems. Furthermore, fructose 2,6-bisphosphate (F26BP) at micromolar concentrations stimulated SuSy2 in the presence of actin while SuSy1 was strongly inhibited by fructose. Possible roles of these two isoforms in the sucrose turnover in BY-2 cells are discussed.
机译：植物酶蔗糖合酶（SuSy; EC 2.4.1.13）催化蔗糖和UDP可逆转化为UDP-葡萄糖（UDP-Glc）和果糖。该酶以不同的同工型存在，并且既位于细胞溶胶中，也与膜结合并且与肌动蛋白的细胞骨架相关。我们在这里研究了烟草（Nicotiana tabacum L.）BY-2异养细胞悬浮液中的蔗糖合酶。可以使用聚（乙二醇）（PEG）沉淀，凝胶过滤，离子交换色谱和亲和色谱的组合，从这些细胞的胞质提取物中纯化出蔗糖合酶SuSy1和SuSy2的两种不同的同工型。它们在离子交换柱的结合以及动力学和调节性能方面都明显不同。 SuSy1是较丰富的物种，与不那么丰富的SuSy2相比，蔗糖和UDP的V_（max）和K_m较低。肌动蛋白刺激SuSy2在分解方向的活性为60％，而SuSy1的抑制作用为17％。 SuSy1和肌动蛋白之间相互作用的迹象是通过在水性葡聚糖-PEG两相系统中分配获得的。此外，在肌动蛋白存在下，微摩尔浓度的果糖2,6-二磷酸（F26BP）刺激了SuSy2，而果糖强烈抑制了SuSy1。讨论了这两种同工型在BY-2细胞中蔗糖周转中的可能作用。

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