Zn2 +调节鸟氨酸transcarbamoylase。二世。金属结合位点。
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李郭LC,卡隆C, S,赫兹伯格W
Zn2 +调节鸟氨酸transcarbamoylase。二世。金属结合位点。
J杂志。1990年1月5日,211 (1):271 - 80。
- PubMed ID
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2405164 (在PubMed]
- 文摘
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两种类型的构象变化介导的大肠杆菌鸟氨酸transcarbamoylase由金属离子锌。在绑定锌的快速均衡,经历一个变构酶过渡。在缺乏底物,zinc-bound酶进一步与相应活动经历了一个缓慢的异构化损失。三种金属离子紧密包裹在异构化酶由凝胶色谱法和原子吸收光谱。由于酶是由相同的亚基组成的三聚物,锌离子是绑定/酶单体。与定点诱变的应用,酶的半胱氨酰残基在273位置已被确定为一个金属配体。锌渣是由丙氨酸取代,不再是一个紧束缚抑制剂,不促进异构化。变更的锌在突变酶的作用是由于减少金属亲和力。突变体酶饱和的金属时,会显示一个内在从野生型的变构效应不变;找到一个相同的希尔系数1.5为锌绑定Ala273和野生型酶。 Cys273 is also a binding site of L-ornithine. At pH 8.5, the Ala273 enzyme binds the substrate analog L-norvaline ten times more weakly and exhibits a kcat/Kmorn that is 27 times less than that of the wild-type enzyme. This finding supports our earlier interpretation that the zinc-induced ornithine co-operativity of ornithine transcarbamoylase is caused by direct competition between L-ornithine and the metal for the same site. As controls, each of the remaining three cysteinyl residues of the bacterial ornithine transcarbamoylase has also been replaced with alanine. These sulfhydryl groups are found not to be related to zinc complexation, ornithine binding or enzyme allostery.