Ueno H, Harrington W F
Proc Natl Acad Sci U S A. 1981 Oct;78(10):6101-5. doi: 10.1073/pnas.78.10.6101.
We have determined the rates of chymotryptic proteolysis of the myosin hinge region in glycerinated rabbit psoas fibers and myofibrils in in rigor-inducing, activating, and relaxing buffers. The time course of formation of light meromyosin (LMM) provides a specific probe for cleavage within the hinge domain. In rigor-inducing and relaxing buffers proteolysis within the hinge is depressed, but on activation LMM is formed at a markedly increased rate, which is dependent on the concentration of MgATP. Peptide bond cleavage occurs at four widely separated sites spanning the length of the hinge domain. Only a trivial amount of proteolysis occurs at the head--rod swivel or within the heavy chain of the head itself (S-1 subunit) in rigor-inducing and relaxing solvents, and we find no significant change on activation. The rate of formation of LMM in rigor-inducing buffer is unchanged by addition of MgADP, Pi, or magnesium adenosine 5'-[beta, gamma-imido]triphosphate or in activating solvent at zero overlap between thick and thin filaments. These results provide evidence for a conformational (helix--coil) transition within the myosin hinge upon activation of skeletal muscle.
我们已经测定了甘油处理的兔腰大肌纤维和肌原纤维中，肌球蛋白铰链区在诱导僵直、激活和松弛缓冲液中的胰凝乳蛋白酶解速率。轻酶解肌球蛋白（LMM）的形成时间进程为铰链结构域内的裂解提供了一个特异性探针。在诱导僵直和松弛缓冲液中，铰链区内的蛋白水解受到抑制，但在激活时，LMM的形成速率显著增加，这取决于MgATP的浓度。肽键裂解发生在跨越铰链结构域长度的四个相距很远的位点。在诱导僵直和松弛溶剂中，在头部-杆部旋转点或头部自身的重链（S-1亚基）内仅发生少量的蛋白水解，并且我们发现在激活时没有显著变化。在诱导僵直缓冲液中加入MgADP、Pi或5'-[β,γ-亚氨基]三磷酸镁腺苷，或在粗细肌丝零重叠的激活溶剂中，LMM的形成速率均不变。这些结果为骨骼肌激活时肌球蛋白铰链区内的构象（螺旋-卷曲）转变提供了证据。
