Phosphorylation of calcium adenosinetriphosphatase by inorganic phosphate: reversible inhibition at high magnesium ion concentrations.
Phosphorylation of calcium adenosinetriphosphatase by inorganic phosphate: reversible inhibition at high magnesium ion concentrations.
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无机磷酸盐对钙腺苷三磷酸酶的磷酸化：高镁离子浓度下的可逆抑制。
DOI：
10.1021/bi00530a026
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发表时间：
1982
期刊：
影响因子：
2.9
通讯作者：
Tanford,C
中科院分区：
文献类型：
--
作者：
Loomis,CR;Martin,DW;McCaslin,DR;Tanford,C
卡森河卢米斯，德怀特W. 1 Darrell R. McCaslin，8和Charles Tanford** 摘要：镁通过无机磷酸盐刺激肌浆网钙泵蛋白的磷酸化，但这种作用被高[Mg 2 +]逆转，这种逆转很容易解释为酶的两种构象状态的普遍接受的存在，E！和E2。E2是酶的一种形式，能被P β磷酸化，并有一个Mg ~（2+）结合位点。Ej是具有两个高亲和力Ca 2+结合位点的酶的形式，并且当Ca 2+结合时，它被ATP磷酸化。Mg ~（2+）可与两个Ca ~（2+）位点和第三个Ca ~（2+）位点弱结合。骨骼肌肌浆网Ca ~（2+）-ATP酶可存在两种主要的构象状态Et和E_2（de Meis & Vianna，1979）。E有两个对Ca ~（2+）高亲和力的位点，一个对ATP高亲和力的位点，可能还有一个对ATP低亲和力的位点。当ATP和Ca ~（2+）结合时，E_1转化为ADP敏感的磷酸酶Ca ~（2+）E_1-P。当两者结合时，可以转化为ADP敏感的磷酸酶MgE 2-P。（Martin & Tanford，1981），我们研究了由未配体的酶（E1 + E2）形成MgE 2-P的热力学。在低Mg ~（2+）浓度下（约10 mM），磷酸化程度服从图1右半部分所示的简单双反应物图解，我们的结果和推导的平衡常数与Punzen-gruber埃塔尔以前的数据一致。（1978年）。然而，在高[Mg 2 +]下，
Carson R. Loomis, Dwight W. Martin, 1 Darrell R. McCaslin, 8 and Charles Tanford** abstract: Magnesium stimulates phosphorylation of the calcium pump protein of the sarcoplasmic reticulum by inorganic phosphate, but the effect is reversed by high [Mg2+], This reversal is readily explained in terms of the generally accepted existence of two conformational states of the enzyme, E! and E2. E2 is the formof the enzyme that can be phos-phorylated by P¡, and it has one binding site for Mg2+. Ej is the form of the enzyme that has two high-affinity Ca2+ binding sites, and it is phosphorylated by ATP when Ca2+ is bound. Mg2+ can bind weakly to the two Ca2+ sites andto a third siteThe Ca2+-ATPase of skeletal muscle sarcoplasmic reticulum can exist in two major conformational states, Et and E2 (de Meis & Vianna, 1979). E, has two high-affinity sites for Ca2+, a high-affinity site for ATP, and possibly a second site of lower affinity forATP. When both ATP and Ca2+ are bound, E, is converted to an ADP-sensitive phosphoenzyme, Ca2E,-P. E2 binds one Mg2+ and one inorganic orthophosphate (P¡)’ion and, when both are bound, can be converted to an ADP-in-sensitive phosphoenzyme, MgE2-P. In a previous paper (Martin & Tanford, 1981), we studied the thermodynamics of formation of MgE2-P from unliganded enzyme (Ej+ E2). At low Mg2+ concentration (to about 10 mM), the extent of phosphorylation was found to obey the simple bireactant scheme shown in the right half ofFigure 1, and our results and derived equilibrium constants were found to be in good agreement with the previous data of Punzen-gruber etal.(1978). At high [Mg2+], however, the extent of