AVIDIN AS A PROBE OF THE CONFORMATIONAL-CHANGES INDUCED IN PYRUVATE-CARBOXYLASE BY ACETYL-COA AND PYRUVATE
AVIDIN AS A PROBE OF THE CONFORMATIONAL-CHANGES INDUCED IN PYRUVATE-CARBOXYLASE BY ACETYL-COA AND PYRUVATE
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DOI：
10.1016/0014-5793(86)80740-2
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发表时间：
1986-07-28
期刊：
影响因子：
3.5
通讯作者：
WALLACE, JC
中科院分区：
文献类型：
--
作者：
ATTWOOD, PV;MAYER, F;WALLACE, JC
将羊肝丙酮酸羧化酶与抗生物素蛋白以1：1的摩尔比混合，存在乙酰辅酶A依赖性或乙酰辅酶A非依赖性活性所需的测定系统组分的各种组合，并通过电子显微镜检查负染色样品。显着数量的链状聚合物的酶-亲和素复合物是显而易见的，只有当乙酰辅酶A或高水平的丙酮酸存在于介质中。鸡肝丙酮酸羧化酶也得到了类似的结果，尽管这种酶几乎完全缺乏乙酰辅酶A的独立活性。因此，虽然乙酰辅酶A和高浓度的丙酮酸可以诱导丙酮酸羧化酶采取一个“紧”四面体样构象，可以与抗生物素蛋白相互作用，形成链，这种结构的变化本身并不导致酶的形式，是最大的活性。这表明乙酰辅酶A对丙酮酸羧化酶的变构激活至少部分归因于更微妙的构象变化，特别是在鸡酶的情况下。
Sheep liver pyruvate carboxylase was mixed with avidin at a molar ratio of 1:1 in the presence of various combinations of the components of the assay systems required for either the acetyl-CoA-dependent or the acetyl-CoA-independent activity and negatively stained samples were examined by electron microscopy. Significant numbers of chain-like polymers of enzyme-avidin complexes were evident only when acetyl-CoA or high levels of pyruvate were present in the media. Similar results were also obtained for chicken liver pyruvate carboxylase despite this enzyme's almost complete lack of acetyl-CoA-independent activity. Thus, although acetyl-CoA and high concentrations of pyruvate may induce pyruvate carboxylase to adopt a ‘tight’ tetrahedron-like conformation which can interact with avidin to form chains, this structural change alone does not result in an enzymic form that is maximally active. This suggests that the allosteric activation of pyruvate carboxylase by acetyl-CoA is attributable, at least in part to more subtle conformational changes, especially in the case of the chicken enzyme.