REVERSIBILITY OF ADENOSINE-TRIPHOSPHATE CLEAVAGE BY MYOSIN
REVERSIBILITY OF ADENOSINE-TRIPHOSPHATE CLEAVAGE BY MYOSIN
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DOI：
10.1042/bj1330323
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发表时间：
1973-01-01
影响因子：
4.1
通讯作者：
TRENTHAM, DR
中科院分区：
文献类型：
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作者：
BAGSHAW, CR;TRENTHAM, DR
对于最简单的动力学模型，在pH8.0和22°C下，在5 mm-MgCl 2、50 mm-KCl和20 mm-Tris-HCl缓冲液中，纯化的兔骨骼肌重肌球蛋白和重肌球蛋白亚片段1与ATP结合和切割相关的反向速率常数（k− 1和k −2）为：k−1<0.02s− 1和k −1= 16 s −1。显然，在纯度较低的蛋白质制备物中发现了较高的k-1和k-2值。k − 1和k − 2的值满足先前关于H218 O掺入Pi部分对ATP水解的研究所要求的条件，并表明裂解步骤确实涉及ATP的水解或ATP与水之间加合物的形成。在肌球蛋白活性位点处的裂解步骤的平衡常数为9。如果肌肉收缩过程中的事件循环是由Wynn和Taylor（1971）提出的模型描述的，那么对于裂解步骤只有小的负标准自由能变化的事实对于肌肉收缩过程中有效的化学能到机械能交换是有利的。
For the simplest kinetic model the reverse rate constants (k−1andk−2) associated with ATP binding and cleavage on purified heavy meromyosin and heavy meromyosin subfragment 1 from rabbit skeletal muscle in the presence of 5mm-MgCl2, 50mm-KCl and 20mm-Tris–HCl buffer at pH8.0 and 22°C are:k−1<0.02s−1andk−1=16s−1. Apparently, higher values ofk−1andk−2are found with less-purified protein preparations. The values ofk−1andk−2satisfy conditions required by previous18O-incorporation studies of H218O into the Pimoiety on ATP hydrolysis and suggest that the cleavage step does involve hydrolysis of ATP or formation of an adduct between ATP and water. The equilibrium constant for the cleavage step at the myosin active site is 9. If the cycle of events during muscle contraction is described by the model proposed by Lymn & Taylor (1971), the fact that there is only a small negative standard free-energy change for the cleavage step is advantageous for efficient chemical to mechanical energy exchange during muscle contraction.