IQUIFIB-Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956, 1113 Buenos Aires, Argentina.
Arch Biochem Biophys. 2010 Mar 1;495(1):62-6. doi: 10.1016/j.abb.2009.12.021. Epub 2009 Dec 24.
The plasma membrane Ca2+ ATPase catalyzed the hydrolysis of ATP in the presence of millimolar concentrations of EGTA and no added Ca2+ at a rate near 1.5% of that attained at saturating concentrations of Ca2+. Like the Ca-dependent ATPase, the Ca-independent activity was lower when the enzyme was autoinhibited, and increased when the enzyme was activated by acidic lipids or partial proteolysis. The ATP concentration dependence of the Ca2+-independent ATPase was consistent with ATP binding to the low affinity modulatory site. In this condition a small amount of hydroxylamine-sensitive phosphoenzyme was formed and rapidly decayed when chased with cold ATP. We propose that the Ca2+-independent ATP hydrolysis reflects the well known phosphatase activity which is maximal in the absence of Ca2+ and is catalyzed by E(2)-like forms of the enzyme. In agreement with this idea pNPP, a classic phosphatase substrate was a very effective inhibitor of the ATP hydrolysis.
质膜 Ca2+ATP 酶在存在 EGTA（一种 Ca2+螯合剂）和无外加 Ca2+的情况下，于毫摩尔浓度下将 ATP 水解，其速率接近在饱和 Ca2+浓度下达到的速率的 1.5%。与 Ca2+依赖性 ATP 酶一样，当酶自动抑制时，非依赖性 Ca2+的活性较低，而当酶被酸性脂质或部分蛋白水解激活时，活性增加。非依赖性 ATP 酶的 ATP 浓度依赖性与 ATP 结合到低亲和力调节位点一致。在这种情况下，形成少量的羟胺敏感的磷酸酶，当用冷 ATP 追踪时，它迅速衰减。我们提出，非依赖性 Ca2+水解反映了众所周知的磷酸酶活性，这种活性在没有 Ca2+的情况下最大，并由酶的 E2 样形式催化。与这一观点一致的是，pNPP（一种经典的磷酸酶底物）是 ATP 水解的非常有效的抑制剂。
