Stafford W F, Szentkiralyi E M, Szent-Györgyi A G
Biochemistry. 1979 Nov 27;18(24):5273-80. doi: 10.1021/bi00591a002.
Calcium control was studied in single-headed myosin and subfragment-1 (S1) preparations obtained by papain digestion of scallop myosin. Single-headed myosin, containing light chains in stoichiometric amounts, was calcium regulated; in contrast, the actin-activated Mg-ATPase of all S1 species lacked calcium sensitivity. Both regulatory and essential light chains were retained by S1 and single-headed myosin preparations provided divalent cations were present during papain digestion, although a peptide amounting to 10% of the mass was removed from regulatory light chains. The modified regulatory light chain retained its ability to confer calcium binding and restore calcium sensitivity to the ATPase of desensitized myofibrils. Regulatory light chains protected the essential light chains from fragmentation by papain. S1 bound regulatory light chains with a uniformly high affinity and appeared to consist of a single species. The results demonstrate that head to head interactions are not obligatory for calcium control, although they may occur in the intact myosin molecule, and suggest a role for the subfragment-2 region in calcium regulation of myosin.
通过木瓜蛋白酶消化扇贝肌球蛋白获得的单头肌球蛋白和亚片段-1（S1）制剂中的钙调控情况得到了研究。含有化学计量比轻链的单头肌球蛋白受钙调节；相反，所有S1种类的肌动蛋白激活的Mg-ATP酶缺乏钙敏感性。如果在木瓜蛋白酶消化过程中存在二价阳离子，S1和单头肌球蛋白制剂会保留调节性轻链和必需轻链，尽管从调节性轻链中去除了占质量10%的一段肽。修饰后的调节性轻链保留了赋予钙结合能力并恢复脱敏肌原纤维ATP酶钙敏感性的能力。调节性轻链保护必需轻链不被木瓜蛋白酶切割。S1以均匀的高亲和力结合调节性轻链，并且似乎由单一物种组成。结果表明，尽管头对头相互作用可能发生在完整的肌球蛋白分子中，但对于钙调控来说并非必不可少，并且表明亚片段-2区域在肌球蛋白的钙调节中发挥作用。
