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来自大肠杆菌的硒代半胱氨酸合酶。反应序列分析。

Selenocysteine synthase from Escherichia coli. Analysis of the reaction sequence.

作者信息

Forchhammer K, Böck A

机构信息

Lehrstuhl für Mikrobiologie, Universität München, Federal Republic of Germany.

出版信息

J Biol Chem. 1991 Apr 5;266(10):6324-8.

PMID:2007585
Abstract

The product of the selA gene, selenocysteine synthase, is a pyridoxal 5-phosphate-containing enzyme which catalyzes the conversion of seryl-tRNA(Sec UCA) into selenocysteyl-tRNA(Sec UCA). Reduction of the aldimine group of pyridoxal 5-phosphate inactivates the enzyme. When reacted with seryl-tRNA(Sec UCA) as sole substrate, pyruvate (and possibly also ammonia) is released; in the presence of a high concentration of potassium borohydride, alanyl-tRNA(Sec UCA) is formed from seryl-tRNA(Sec UCA). These results support the notion that the formyl group of pyridoxal phosphate forms a Schiff base with the alpha-amino group of L-serine with the subsequent 2,3-elimination of a water molecule and the generation of an aminoacrylyl-tRNA(Sec UCA) intermediate. ATP is not required for this reaction step, but it is necessary for the conversion of aminoacrylyl-tRNA into selenocysteyl-tRNA(Sec UCA) which, in addition, requires the SELD protein and reduced selenium. Selenocysteine synthase forms a stable complex with seryl-tRNA(Sec UCA) with one tRNA molecule bound per two 50-kDa monomers. The enzyme does not interact with serine-inserting tRNA species. Taken together, the results show that biosynthesis of selenocysteine takes place in the enzyme-bound state and involves the dehydration of L-serine esterified to tRNA in a first step formally followed by the 2,3-addition of HSe- which is provided by the SELD protein in an ATP-dependent reaction in the form of a reactive selenium donor molecule.

摘要

硒代半胱氨酸合酶基因(selA)的产物是一种含磷酸吡哆醛的酶,它催化丝氨酰 - tRNA(Sec UCA)转化为硒代半胱氨酰 - tRNA(Sec UCA)。磷酸吡哆醛的醛亚胺基团还原会使该酶失活。当与丝氨酰 - tRNA(Sec UCA)作为唯一底物反应时,会释放出丙酮酸(可能还有氨);在高浓度硼氢化钾存在的情况下,丝氨酰 - tRNA(Sec UCA)会形成丙氨酰 - tRNA(Sec UCA)。这些结果支持了这样一种观点,即磷酸吡哆醛的甲酰基与L - 丝氨酸α - 氨基形成席夫碱,随后2,3 - 消除一个水分子并生成氨基丙烯酰 - tRNA(Sec UCA)中间体。该反应步骤不需要ATP,但将氨基丙烯酰 - tRNA转化为硒代半胱氨酰 - tRNA(Sec UCA)需要ATP,此外还需要SELD蛋白和还原态硒。硒代半胱氨酸合酶与丝氨酰 - tRNA(Sec UCA)形成稳定复合物,每两个50 kDa单体结合一个tRNA分子。该酶不与插入丝氨酸的tRNA种类相互作用。综上所述,结果表明硒代半胱氨酸的生物合成是在酶结合状态下进行的,第一步涉及与tRNA酯化的L - 丝氨酸脱水,随后正式进行由SELD蛋白以反应性硒供体分子形式在ATP依赖性反应中提供的HSe - 的2,3 - 添加。

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