Grassi de Gende A O, Alonso G L
J Mol Cell Cardiol. 1985 May;17(5):505-9. doi: 10.1016/s0022-2828(85)80055-9.
The effect of [Ca2+] on (Ca2+ + Mg2+)-ATPase activity from dog heart sarcoplasmic reticulum fragments was evaluated under three different pH values: 6.0, 6.8 and 7.6. Considering pH 6.8 as reference, under pH 7.6 an increase of the activity at saturating [Ca2+], an increase of pCa needed for half-maximal activation, and a decrease of the Hill coefficient, were observed. Opposite results were obtained under pH 6.0. The positively cooperative effect of Ca2+ was only observed at the lowest pH. The results are in line with previous suggestions regarding the existence of two enzymatic states with different Ca2+ affinities; this paper suggests as well, that equilibrium between these states is affected by pH. The results are compared with data obtained with skeletal sarcoplasmic reticulum fragments under the same experimental conditions.
在三种不同的pH值（6.0、6.8和7.6）下，评估了[Ca2+]对犬心脏肌浆网片段中（Ca2+ + Mg2+）-ATP酶活性的影响。以pH 6.8为参照，在pH 7.6时，观察到在饱和[Ca2+]下活性增加、半最大激活所需的pCa增加以及希尔系数降低。在pH 6.0时得到了相反的结果。Ca2+的正协同效应仅在最低pH值时观察到。这些结果与之前关于存在两种具有不同Ca2+亲和力的酶状态的建议一致；本文还表明，这些状态之间的平衡受pH影响。将这些结果与在相同实验条件下用骨骼肌浆网片段获得的数据进行了比较。
