Succinyl coenzyme A synthetase of Escherichia coli. Effects of phosphoenzyme formation and of substrate binding on the reactivity and stability of the enzyme.
Succinyl coenzyme A synthetase of Escherichia coli. Effects of phosphoenzyme formation and of substrate binding on the reactivity and stability of the enzyme.
复制标题
大肠杆菌的琥珀酰辅酶A合成酶。
DOI：
10.1016/s0021-9258(17)42749-9
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发表时间：
1972
期刊：
影响因子：
--
通讯作者：
W. A. Bridger
中科院分区：
文献类型：
--
作者：
F. J. Moffet;T. Wang;W. A. Bridger
摘要大肠杆菌琥珀酰辅酶A合成酶的两个活性位点中只有一个位点形成磷酸组氨酸，导致酶的反应性发生深刻变化。在储存时，去磷酸化形式的酶以约100倍于单磷酸化形式的速率失去活性。类似地，胰蛋白酶对磷酸化和去磷酸化酶的失活速率存在两个数量级的差异。失活的速率和程度与酶的磷酸化状态直接相关。与底物相互转化酶的磷酸化和去磷酸化形式的能力保持一致，ATP保护先前去磷酸化的酶免受蛋白水解攻击，而琥珀酸和Mg++的存在使先前磷酸化的酶对蛋白水解敏感。不仅用胰蛋白酶，而且用具有不同特异性的多种蛋白酶观察到这些效应。结果表明，磷酸化的1个活性位点组氨酸残基每个寡聚酶分子的结果在一个显着的变化，在三维结构的酶，以更紧密的构象，伴随着稳定性，也许，扭曲的第二个活性位点的分子，使其磷酸化是不利的。
Abstract Formation of phosphohistidine at only one of an apparent total of two active sites in Escherichia coli succinyl coenzyme A synthetase results in profound changes in the reactivity of the enzyme. On storage, the dephosphorylated form of enzyme loses activity at a rate approximately 100 times that of the monophosphorylated form. Similarly, there is a difference of two orders of magnitude in the rates of inactivation by trypsin of the phosphorylated and dephosphorylated enzymes. There is direct correlation between both the rate and extent of inactivation and the status of phosphorylation of the enzyme. In keeping with the ability of substrates to interconvert the phosphorylated and dephosphorylated forms of enzyme, ATP protects the previously dephosphorylated enzyme from proteolytic attack, whereas the presence of succinate and Mg++ renders previously phosphorylated enzyme susceptible to proteolysis. These effects are observed not only with trypsin, but with a variety of proteases having different specificities. The results indicate that phosphorylation of 1 active site histidine residue per oligomeric enzyme molecule results in a significant change in the three-dimensional structure of the enzyme to a tighter conformation, with concomitant stability and, perhaps, distortion of the second active site in the molecule so that its phosphorylation is unfavorable.