MECHANISM OF MUSCULAR CONTRACTION
MECHANISM OF MUSCULAR CONTRACTION
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DOI：
10.1126/science.164.3886.1356
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发表时间：
1969-01-01
期刊：
影响因子：
56.9
通讯作者：
HUXLEY, HE
中科院分区：
文献类型：
--
作者：
HUXLEY, HE
《科学》第164卷，关于I带中的肌动蛋白丝。因此，很明显，它们形成了肌球蛋白丝结构的永久部分。由于它们是肌动蛋白和肌球蛋白丝之间产生力的唯一可见的机械因子，因此有人认为（4）这确实是它们的功能，而且它们很可能代表肌球蛋白分子的重裂肌球蛋白亚基。已经知道肌动蛋白结合能力和腺苷三磷酸酶活性与分子的这一部分有关（7），并且似乎可以合理地假设，对这些特性负责的位点将以这样一种方式构建在肌肉的整体结构中，即它们可以直接与肌动蛋白丝相互作用。在肌肉收缩过程中，即使是一次抽搐，其结构也可能比原来的长度缩短30%或更多，因此肌动蛋白和肌球蛋白细丝必须在每半个肌节中相互滑动0.375微米（即3750埃）（在青蛙肌肉中，静止肌节长度为2.5微米）。在电子显微照片中可以看到横桥取向的一些变化，但是如果桥精确地垂直于粗丝，则远端似乎从未从它们所占据的位置移位超过约100埃。因此，很明显，为了产生更大的整体滑动运动，横桥与肌动蛋白丝之间的某种重复相互作用是必要的。一种可能性是，横桥以周期性方式来回移动，附着在肌动蛋白丝上，并在其行程的一部分将其拉向A带的中心，并在其返回行程之前再次分离。另一种可能是，横桥可能保持刚性固定在位置上，而肌动蛋白丝的重复性内部变化使它们能够沿着这样提供的一系列固定点爬行。但无论细节如何，基本的想法是，当力产生时，横桥与肌动蛋白丝直接接触，它们是传递力的机械媒介。由于化学反应的可能自由能显然最
SCIENCE, VOL. 164 on the actin filaments in the I-bands. It was clear, therefore, that they formed a permanent part of the myosin fila-ment structure. As they were the only visible mechanical agents by which a force could be developed between the actin and myosin-filaments, it was suggested (4) that this indeed was their function, and that they very probably represented the heavy-meromyosin subunit of the myosin molecule. It was already known that the actin-combining ability and adenosine triphosphatase activity were associated with this part of the molecule (7), and it seemed rea-sonable to suppose that the sites re-sponsible for these properties would be built into the overall structure ofthe muscle in such a way thatthey could in-teract directly with the actin filaments. During the contraction ofa muscle, even during a single twitch, the struc-ture may shortenby 30 percent of its original length or more, and the actin and myosin filaments must therefore slide past each other (in a frog muscle starting at a resting sarcomere length of 2.5 microns) by 0.375 microns (that is, 3750 angstroms) in each half-sarcomere. Some variation in orientation of the cross-bridges can be seen in electron micrographs, but the distal ends never seem to be displaced by more than about 100 angstroms from the position they would occupy if the bridges were accurately perpendicular to the thick filaments. It is clear thereforethat, in order to produce the much larger over-all sliding movement, some type of re-petitive interaction of the cross-bridges with the actin filaments is necessary. One possibility might be that the cross-bridges move to and fro in a cyclical manner, attaching to the actin fila-ments and pulling them toward the center of theA-band on one part of their stroke, and detaching again prior to their return stroke. Alternatively, the cross-bridges might remain rigidly fixed in position while repetitive internal changes in the actin filaments enabled them to crawlalong the series of fixed points so provided. But whatever the details, the basic idea was that the cross-bridges were in direct contact with the actin filaments when force was developed, and that they were the me-chanical agents through which the force was transmitted. Since the probable free energy of the chemical reaction apparently most