Zhu Bin, Wan Chao-min, Liu Rong-tao, Sun Ai-min, Huang Sun, Wang Zheng-rong
Space Med Med Eng (Beijing). 2002 Oct;15(5):355-8.
Objective. To study the influence of Ca2+ and Mg2+ 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 Vmax 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 Ca2+, Mg(2+)-activated myosin ATPase at high ionic [correction of ironic] strength were 5.27 +/- 2.10 mmol, 7.04 +/- 2.06 mmol and the Vmax values were 1.10 +/- 0.13 micromoles mg-1 min-1, 0.617 +/- 0.09 micromoles mg-1 min-1 respectively. The Km of Ca(2+)-activated ATPase was higher than that of Mg(2+)-activated ATPase. But the ATPase activity of Ca2+ was influenced by the concentrations of MgCl2. The effect of Ca(2+)-activated ATPase increase was found at lower MgCl2 concentrations. As the MgCl2 concentration increased above 6 mmol/L, Ca2+ 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 Ca2+ and Mg2+ effect on myosin ATPase were different. Mg2+ is essential to maintain the conformation of enzymatic activity of myosin in cardiac muscle contraction. Ca2+ is likely acted as a role conducting signals and regulating function.
目的。研究Ca2+和Mg2+对心肌肌球蛋白酶活性的影响。方法。描述了一种从兔心脏左心室纯化肌球蛋白的简便方法。根据酶促反应中Pi释放速率，测定Ca(2+)激活和Mg(2+)激活的ATP酶的Km和Vmax，以及不同离子浓度和不同pH范围内对肌球蛋白ATP酶酶活性的影响。结果。在高离子强度下，Ca2+、Mg(2+)激活的肌球蛋白ATP酶的Km值分别为5.27±2.10 mmol、7.04±2.06 mmol，Vmax值分别为1.10±0.13微摩尔mg-1 min-1、0.617±0.09微摩尔mg-1 min-1。Ca(2+)激活的ATP酶的Km高于Mg(2+)激活的ATP酶。但Ca2+的ATP酶活性受MgCl2浓度的影响。在较低的MgCl2浓度下发现Ca(2+)激活的ATP酶活性增加。当MgCl2浓度增加到6 mmol/L以上时，Ca2+敏感性降低。pH-活性曲线表明，Mg(2+)激活的肌球蛋白ATP酶活性比Ca(2+)激活的更稳定。结论。Ca2+和Mg2+对肌球蛋白ATP酶的作用机制不同。Mg2+对于维持心肌收缩中肌球蛋白酶活性的构象至关重要。Ca2+可能起到传导信号和调节功能的作用。
