Kameyama T
J Biochem. 1980 Feb;87(2):581-6. doi: 10.1093/oxfordjournals.jbchem.a132781.
The effect of F-actin on the conformation around a specific thiol group, S2, in heavy meromyosin was investigated. The extent of the change was estimated from the residual activity of Ca2+-ATPase after modifying the thiol with N-ethylmaleimide (NEM). Experiments were carried out with a modified heavy meromyosin (HMM), in which S1 had been blocked with NEM, to observe the reactivity of S2 alone. 1. F-Actin markedly increased the ATP-induced conformational change around S2, but did not affect the adenylyl imidodiphosphate (AMPPNP)-induced change, and markedly supressed the adenylyl methylenediphosphate (AMPPCP)-induced change. 2. The initial burst of HMM ATPase was retained after the modification of S1. Replacement of Mg2+ with Mn2+ in the medium reduced the cooperative action of F-actin and ATP with concomitant loss of the initial burst. 3. Nevertheless, F-actin was capable of activating the steady-state ATPase activity of HMM even in the presence of Mn2+. 4. The degree of activation by F-actin of the ATP-induced increase in the reactivity of S2 did not parallel that of the steady-state ATP splitting, when the KCl concentration of the medium was varied. The results indicate that the actin-induced local conformational change in the S2 region is related to an energized state of the myosin molecule caused by Mg2+-ATP, but is apparently not related to the actin-activated steady-state ATPase activity.
研究了F-肌动蛋白对重酶解肌球蛋白中特定硫醇基团S2周围构象的影响。在用N-乙基马来酰亚胺（NEM）修饰硫醇后，根据Ca2+ -ATP酶的残余活性估计变化程度。使用一种修饰的重酶解肌球蛋白（HMM）进行实验，其中S1已被NEM阻断，以单独观察S2的反应性。1. F-肌动蛋白显著增加了ATP诱导的S2周围构象变化，但不影响腺苷酰亚胺二磷酸（AMPPNP）诱导的变化，并显著抑制腺苷酰亚甲基二磷酸（AMPPCP）诱导的变化。2. 在S1修饰后，HMM ATP酶的初始爆发得以保留。培养基中用Mn2+替代Mg2+降低了F-肌动蛋白和ATP的协同作用，同时初始爆发消失。3. 然而，即使在存在Mn2+的情况下，F-肌动蛋白仍能够激活HMM的稳态ATP酶活性。4. 当培养基的KCl浓度变化时，F-肌动蛋白对ATP诱导的S2反应性增加的激活程度与稳态ATP水解程度不平行。结果表明，肌动蛋白诱导的S2区域局部构象变化与Mg2+ -ATP引起的肌球蛋白分子的高能状态有关，但显然与肌动蛋白激活的稳态ATP酶活性无关。
