Clarke M L, Rodger C D, Tregear R T
J Muscle Res Cell Motil. 1984 Feb;5(1):81-96. doi: 10.1007/BF00713153.
Substitution of ethylene glycol for part of the solvent water changes the mechanical properties, structure and nucleotide binding of glycerol-extracted flight muscle fibres from the waterbug Lethocerus. On addition of ethylene glycol the rigor tension falls, rapidly and reversibly. With increasing glycol concentration the effect saturates at a non-zero tension. The isotonic stiffness is unchanged on adding ethylene glycol. Adding MgAMPPNP (adenylylimidodiphosphate) to a muscle fibre in 50% ethylene glycol causes a further rapid tension fall; above 100 microM AMPPNP the tension reaches zero. The isotonic stiffness of restretched muscle is then close to that of a relaxed fibre. Removal of MgAMPPNP from the bathing medium has no immediate mechanical effect. After several hours the isotonic stiffness rises to some extent; on removal of the glycol both tension and stiffness rise to rigor values within one minute. 3H-Labelled AMPPNP binds to muscle fibres in 50% ethylene glycol in a similar amount to the number of myosin heads present. The binding is tighter than that in aqueous solution and the nucleotide is only released very slowly. Upon removal of the ethylene glycol nucleotide is rapidly released. X-ray diffraction of muscle in 50% ethylene glycol reveals a highly ordered structure, in which both the 14 nm and the 38 nm layer lines are sharply sampled and are of intermediate values between rigor and relaxation. The two inner equatorial peaks are also of intermediate values. On adding MgAMPPNP the pattern resembles that of relaxed muscle. Upon removal of the nucleotide the pattern does not revert towards rigor but on removal of glycol it does. These results are interpreted in terms of changes within the myosin heads and their array within the filament lattice.
用乙二醇替代部分溶剂水会改变仰泳蝽甘油提取的飞行肌纤维的机械性能、结构和核苷酸结合。加入乙二醇后，强直张力迅速且可逆地下降。随着乙二醇浓度的增加，这种效应在非零张力下达到饱和。加入乙二醇时，等张刚度不变。向50%乙二醇中的肌纤维添加MgAMPPNP（腺苷酰亚胺二磷酸）会导致张力进一步快速下降；在100 microM以上的AMPPNP时，张力降至零。重新拉伸的肌肉的等张刚度随后接近松弛纤维的等张刚度。从浴液中去除MgAMPPNP没有立即产生机械效应。几小时后，等张刚度在一定程度上上升；去除乙二醇后，张力和刚度在一分钟内升至强直值。3H标记的AMPPNP以与存在的肌球蛋白头部数量相似的量结合到50%乙二醇中的肌纤维上。这种结合比在水溶液中更紧密，核苷酸释放非常缓慢。去除乙二醇后，核苷酸迅速释放。50%乙二醇中肌肉的X射线衍射显示出高度有序的结构，其中14纳米和38纳米的层线都被清晰采样，且处于强直和松弛之间的中间值。两个内赤道峰也处于中间值。加入MgAMPPNP后，模式类似于松弛肌肉的模式。去除核苷酸后，模式不会恢复到强直状态，但去除乙二醇后会恢复。这些结果是根据肌球蛋白头部内的变化及其在细丝晶格中的排列来解释的。
