Effects of actin and calcium ion on chymotryptic digestion of skeletal myosin and their implications to the function of light chains.
Effects of actin and calcium ion on chymotryptic digestion of skeletal myosin and their implications to the function of light chains.
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DOI：
10.1021/bi00565a024
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发表时间：
1980-11
期刊：
影响因子：
2.9
通讯作者：
S. Oda;C. Oriol-Audit;E. Reisler
中科院分区：
文献类型：
--
作者：
S. Oda;C. Oriol-Audit;E. Reisler
已经进行了实验以评估肌球蛋白轻链[通过用5，5'-二硫代双（2-硝基苯甲酸）（Nbs2）处理肌球蛋白获得]在控制横桥运动和肌动球蛋白相互作用中的参与。肌球蛋白、肌动球蛋白和肌原纤维的糜蛋白酶消化未检测到肌球蛋白亚片段2区域中任何Ca 2+诱导的变化。肌动蛋白，如Ca 2+，保护原位Nbs2轻链的蛋白水解，并导致部分开关的消化产物的肌球蛋白从亚片段1重裂肌球蛋白。这种效果是独立的肌球蛋白的聚集状态，并坚持在acto重meromyosin和放线菌球蛋白在0.6 M NaCl。消化和沉降研究表明，不存在直接的acto轻链相互作用。肌球蛋白的蛋白质水解显示出从产生重肌球蛋白到亚片段1的逐渐过渡，随着盐水平的降低。在Ca2+的存在下，在聚合肌球蛋白和单体肌球蛋白的双链中产生重肌球蛋白。这些结果被解释在Nbs2轻链和亚片段1内的局部变化。在肌球蛋白头部的亚基相互作用导致Ca2+诱导的重肌球蛋白的亲和力降低肌动蛋白在MgATP的存在下。在高盐浓度（75 mM KCl）下可以检测到肌动蛋白激活的肌球蛋白ATP酶的Ca2+抑制。
Experiments have been carried out to assess the involvement of the myosin light chains [obtained by treatment of myosin with 5,5'-dithiobis(2-nitrobenzoic acid) (Nbs2)] in the control of cross-bridge movement and actomyosin interactions. Chymotryptic digestions of myosin, actomyosin, and myofibrils do not detect any Ca2+-induced change in the subfragment 2 region of myosin. Actin, like Ca2+, protects the in situ Nbs2 light chains from proteolysis and causes a partial switch in the digestion product of myosin from subfragment 1 to heavy meromyosin. This effect is independent of the state of aggregation of myosin, and it persists in acto heavy meromyosin and in actinomyosin in 0.6 M NaCl. Digestions and sedimentation studies indicate that there is no direct acto light chain interaction. Proteolysis of myosin shows a gradual transition from production of heavy meromyosin to subfragment 1 with lowering of the salt level. In the presence of Ca2+ heavy meromyosin is generated both in digestions of polymeric and of monomeric myosin. These results are explained in terms of localized changes within the Nbs2 light chains and subfragment 1. Subunit interactions in the myosin head lead to a Ca2+-induced reduction in the affinity of heavy meromyosin for actin in the presence of MgATP. The resulting Ca2+ inhibition of the actin-activated ATPase of myosin can be detected at high salt concentrations(75 mM KCl).