Ca^(2+)、Mg^(2+)对心肌肌球蛋白ATP酶活性的影响

Effects of Ca^(2+) and Mg^(2+) on the Enzymatic Properties of Cardiac Muscle Myosin.

目的研究Ca2 +、Mg2 +对心肌肌球蛋白ATP酶活性的影响。方法采用一种简便、快速的方法从心肌组织中提取肌球蛋白 ,根据酶反应ATP分解释放的无机磷含量检测Ca2 +、Mg2 +激活肌球蛋白ATP酶的Km值及最大反应速度Vmax,以及不同浓度的Ca2 +、Mg2 +、pH值对肌球蛋白ATP酶活性的影响。 结果Ca2 +、Mg2 +-肌球蛋白ATP酶Km值为 5 .2 7± 2 .1 0mmol、7.0 4± 2 .0 6mmol,Vmax分别为 :1 .1 0± 0 .1 3μmol·mg- 1 ·min- 1 、0 .61 7± 0 .0 9μmol·mg- 1 ·min- 1 ;Ca2 +较Mg2 +具有较大的酶激活能力 (P <0 .0 1 ) ,但Mg2 +的浓度影响着肌球蛋白ATP酶对Ca2 +的敏感性 ,当Mg2 +浓度大于 6mmol/L时 ,酶对Ca2 +的存在无反应 ;不同的pH值 ,对Mg2 +激活的酶反应影响较小。结论Ca2 +、Mg2 +对肌球蛋白ATP酶的作用机理不同 ,Mg2 +是维系肌球蛋白具有酶活性构象所必需 ,而Ca2

Objective To study the influence of Ca 2+ and Mg 2+ on the enzymatic properties of cardiac muscle myosin. Method A convenient method for the purification myosin from the left ventricle of rabbit heart was described. The Km and V max of Ca 2+ activated and Mg 2+ activated ATPase and the effects on the enzymatic properties of myosin ATPase in different ionic concentration and different pH range were determined from the rate of Pi release in enzymatic reaction. Result The Km values of Ca 2+ ?Mg 2+ activated myosin ATPase at high ironic strength were 5.27±2.10 mmol?7.04±2.06 mmol and the V max values were 1.10±0.13 μmol·mg -1 ·min -1 ?0.617±0.09 μmol·mg -1 ·min -1 respectivily. The Km of Ca 2+ activated ATPase was higher than that of Mg 2+ activated ATPase. But the ATPase activity of Ca 2+ was influenced by the concentrations of MgCl 2 .The effect of Ca 2+ activated ATPase increase was found at lower MgCl 2 concentrations. As the MgCl 2 concentration increased above 6 mmol/L, Ca 2+ sensitivity was decreased. The pH activity profiles showed that Mg 2+ activated myosin ATPase activity was more stable than that of Ca 2+ activated. Conclusion The mechanism of Ca 2+ and Mg 2+ effect on myosin ATPase were different. Mg 2+ is essential to maintain the conformation of enzymatic activity of myosin in cardiac muscle contraction. Ca 2+ is likely acted as a role conducting signals and regulating function.