ENERGETICS AND MECHANISM OF ACTOMYOSIN ADENOSINE-TRIPHOSPHATASE
ENERGETICS AND MECHANISM OF ACTOMYOSIN ADENOSINE-TRIPHOSPHATASE
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DOI：
10.1021/bi00671a020
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发表时间：
1976-01-01
期刊：
影响因子：
2.9
通讯作者：
TAYLOR, EW
中科院分区：
文献类型：
--
作者：
WHITE, HD;TAYLOR, EW
测定了肌动蛋白与亚片段1 （S1）、S1-产物复合物、重肌球蛋白（HMM）和HMM-产物复合物在一定温度、pH值和离子强度范围内的反应速率常数。对于肌动蛋白浓度高达10。M，产物中间体的再结合速率等于肌动球蛋白亚片段1 （action - s1）或action - hmm atp酶的速率。因此，在这些条件下，ATP水解的唯一重要途径是通过S1或HMM的解离和重组。S1和S1产物与肌动蛋白结合的表观速率常数也表现出类似的大离子强度依赖性。S1-生成物反应的温度依赖性与act -S1 ATPase的速率相当，而S1-生成物反应随温度的变化较小。表观速率常数不能测量简单的二阶反应。一个合理的机制是结合步骤的快速平衡，然后是一个过渡（产物释放），增加了结合常数。难熔态也会降低复合的表观速率常数。基于对现有证据和S1 atp酶平衡常数的解释，对动作-S1 atp酶反应的平衡常数进行了近似赋值。
Rate constants were determined for the reaction of actin with subfragment 1 (S1), S1-product complex, heavy meromyosin (HMM) and HMM-products complex for a range of temperatures, pH and ionic strengths [in rabbit muscle]. For actin concentrations up to 10 .mu.M, the rate of reassociation of the product intermediate was equal to the rate of actomyosin subfragment 1 (acto-S1) or acto-HMM ATPase. Therefore, under these conditions, the only important pathway for ATP hydrolysis was through the dissociation and recombination of S1 or HMM. The apparent rate constants for the association of S1 and S1-product with actin showed a similar large ionic strength dependence. The S1-product reaction had a large temperature dependence paralleling the rate of acto-S1 ATPase, while the reaction with S1 had a much smaller variation with temperature. The apparent rate constant did not measure a simple 2nd order reaction. A plausible mechanism was a rapid equilibrium for the binding step, followed by a transition (product release) which increased the association constant. A refractory state could also reduce the apparent rate constant of recombination. An approximate assignment of equilibrium constants for the acto-S1 ATPase reaction was made based on the interpretation of the present evidence and equilibrium constants for the S1 ATPase.