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首页> 外文期刊>The biochemical journal >Wheat-germ aspartate transcarbamoylase. Steady-state kinetics and stereochemistry of the binding site for l-aspartate
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Wheat-germ aspartate transcarbamoylase. Steady-state kinetics and stereochemistry of the binding site for l-aspartate

机译：小麦胚芽天冬氨酸转基氨基甲酰基。 L-天冬氨酸粘结位点的稳态动力学和立体化学

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p1. The steady-state kinetics of the bisubstrate reaction catalysed by aspartate transcarbamoylase purified from wheat (Triticum vulgare)-germ have been studied at 25 degrees C, pH 8.5 AND I 0.10-0.12. Initial-velocity and product-inhibition results are consistent with an ordered sequential mechanism in which carbamoyl phosphate is the first substrate to bind, followed by L-aspartate, and carbamoyl aspartate is the first product to leave, followed by Pi. The order of substrate addition is supported by dead-end inhibition studies using pyrophosphate and maleate as inhibitory analogues of the substrates. Product inhibition permitted a minimum value for the dissociation constant of L-aspartate from the ternary complex to be estimated. This minimum is of the same order as the dissociation constant (Ki) of succinate. 2. A range of dicarboxy analogues of L-aspartate were tested as possible inhibitors of the enzyme. These studies suggested that L-aspartate is bound with its carboxy groups in the eclipsed configuration, and that the stereochemical constraints around the binding site are very similar to those reported for the catalytic subunit of the enzyme from Escherichia coli [Davies, Vanaman & Stark (1970) J. Biol. Chem. 245, 1175-1179]./p
机译：> 1。已经在25℃，pH8.5和I.10-0.12中研究了由小麦（Triticum vulgare）纯化的天冬氨酸转基氨基酰基溶解的稳态动力学通过从小麦（Triticum vulgare）-germ纯化的纯化物催化。初始速度和产物抑制结果与有序顺序机制一致，其中氨基酰磷酸盐是第一种结合的基材，其次是L-天冬氨酸，并且氨基甲酰天冬氨酸是第一个离开的产物，其次是PI。使用焦磷酸盐和马来酸作为基材的抑制性类似物，通过止血抑制研究支持基材的顺序。产品抑制允许估计三元复合物的L-天冬氨酸解离常数的最小值。这最小值与琥珀酸的解离常数（ki）相同。 2.作为酶的可能抑制剂测试L-天冬氨酸的一系列二羧基类似物。这些研究表明，L-天冬氨酸与其羧基的羧基在野外配置中结合，并且结合位点周围的立体化学约束与来自大肠杆菌的酶的催化亚基的那些非常相似[戴维斯，Vanaman＆amp; Stark（1970）J. Biol。化学。 245,1175-1179]。

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