Gómez-Puyou A, Ayala G, Muller U, Tuena de Gómez-Puyou M
J Biol Chem. 1983 Nov 25;258(22):13673-9.
ATP hydrolysis, the exchange of inorganic phosphate with ATP, and ATP synthesis have been studied as a function of Mg2+ concentration in bovine heart submitochondrial particles. The rate of exchange is low at concentrations of Mg2+ below 3 mM, at higher concentrations, the exchange is several times higher. ATP hydrolysis shows a different pattern with respect to the concentration of Mg2+. The ratio of ATP hydrolyzed to ATP exchanged is above 20 at Mg2+ concentrations below 3 mM and about 5 at high Mg2+ concentrations; ADP induces a further drop of the ratio (2-3). By assays of the sensitivity of the hydrolytic reaction to organic solvents (dimethyl sulfoxide), it has been possible to determine the rate-limiting step of ATP hydrolysis. At 3 mM Mg2+, the rate-limiting step is the release of ADP in the soluble, but not in the particulate enzyme. However at higher Mg2+ concentrations, the rate-limiting step in the particulate enzyme is also ADP release. Therefore, the decrease in the ratio of ATP hydrolysis to inorganic phosphate incorporated into ATP coincides with a change in the kinetics of the enzyme, i.e. when the terminal step of ATP hydrolysis becomes rate-limiting, the inorganic phosphate-ATP exchange increases. Ca2+ induces an increase in the phosphate-ATP exchange at low Mg2+ concentrations.
在牛心亚线粒体颗粒中，已研究了ATP水解、无机磷酸与ATP的交换以及ATP合成作为Mg2+浓度的函数关系。在Mg2+浓度低于3 mM时，交换速率较低，在较高浓度时，交换速率高出几倍。ATP水解相对于Mg2+浓度呈现出不同的模式。在Mg2+浓度低于3 mM时，水解的ATP与交换的ATP的比率高于20，而在高Mg2+浓度时约为5；ADP会导致该比率进一步下降（至2 - 3）。通过测定水解反应对有机溶剂（二甲基亚砜）的敏感性，得以确定ATP水解的限速步骤。在3 mM Mg2+时，限速步骤是可溶性酶而非颗粒性酶中ADP的释放。然而，在较高Mg2+浓度时，颗粒性酶中的限速步骤也是ADP的释放。因此，ATP水解与掺入ATP中的无机磷酸的比率下降与酶动力学的变化相吻合，即当ATP水解的终末步骤成为限速步骤时，无机磷酸 - ATP交换增加。在低Mg2+浓度下，Ca2+会诱导磷酸 - ATP交换增加。
