A kinetic study of salt-induced denaturation of actin during storage at low temperature

少量的F-肌动球蛋白复合物在加热时作为游离肌球蛋白分子的交联剂，并且它被认为是肌动蛋白诱导的肌球蛋白凝胶形成性改善的先决条件。因此，肌球蛋白热诱导凝胶的性质取决于肌动蛋白在盐处理过程中的稳定性。本工作旨在阐明低温孵育过程中盐诱导肌动蛋白变性的机制.动力学分析表明，肌动蛋白溶液在低温（0 ℃）下的变性遵循不可逆连续反应（F-ADP-actin --> G-ADP-actin -->变性肌动蛋白）理论.向F-肌动蛋白溶液中加入足够量的ATP有效地延缓了肌动蛋白变性的进程。ATP被认为在盐处理期间稳定解聚的G-肌动蛋白的结构。即ATP的存在延缓了G-ADP-肌动蛋白→变性肌动蛋白的过程.很明显，少量的HMM在0 ℃孵育期间加速了F-肌动蛋白的解聚速率。因此，释放的G-肌动蛋白被推测在没有ATP的情况下快速进入变性过程。当将原肌球蛋白加入到含有单独的肌动蛋白或肌动蛋白-HMM复合物的溶液中时，在0.2 M KCl和0.6 M KCl之间，肌动蛋白的变性被显著抑制。从这个结果可以清楚地看出，在低于0.6 M的离子强度下，原肌球蛋白稳定肌动蛋白丝，防止其解体。

The small amount of F-actomyosin complex acts as a cross-linker with the free myosin molecule on heating, and it is considered to be a prerequisite for actin-induced improvement in the gel formability of myosin. Therefore, the property of heat-induced gel of myosin depends on the stability of actin during treatment with salt. The present work was conducted to elucidate the mechanism of salt-induced denaturation of actin during incubation at a low temperature.1. A kinetic analysis by measuring DNase l inhibition capacity of actin demonstrated that the denaturation of actin obeys the theory of an irreversible continuous reaction (F-ADP-actin ---> G-ADP-actin ---> denatured actin) when actin solution is incubated at a low temperature (0ﾟC).2. The addition of a sufficient amount of ATP to an F-actin solution effectively retards the progress of the denaturation of actin. ATP is thought to stabilize the structure of G-actin depolymerized during treatment with salt. That is, the present of ATP retards the process of G-ADP-actin -->denatured actin.3. It has become apparent that a small amount of HMM accelerates the rate of depolymerization of F-actin during incubation at 0ﾟC.As a result, released G-actin is presumed to enter quickly the denaturation process without ATP.4. When tropomyosin was added to solution containing actin alone or actin-HMM complex, the denaturation of actin was suppressed remarkably between 0.2 M KCI and 0.6 M KCI.From this result, it is clear that tropomyosin stabilizes the actin filament against disassembly at ionic strengths lower than 0.6 M.KCI