Structure and function of Heads A and B of Myosin

利用A、B两头肌球蛋白氨基酸序列的差异，制备了针对A头和B头肌球蛋白的抗体。我们研究了是否有一个肌球蛋白分子具有A-B杂二聚体结构。结果表明，存在A和B两个不同的头部。我们用这种方法固定了与不溶性物质结合的蛋白-A的抗体，并检测了肌球蛋白或肌球蛋白头S-1是否能与这些抗体结合。我们发现，几乎所有添加的肌球蛋白都被抗A或抗B抗体吸收。因此，我们得出结论，大部分肌球蛋白分子具有A-B杂二聚体结构。除了第86个反应性赖氨酸残基附近的氨基酸序列外，肌球蛋白分子头部A和B的化学结构的差异尚不清楚。然后，我们用针对两个头部的抗体研究了S-1的胰酶消化。S-1用胰酶消化时，肌球蛋白重链(100 KDa)被消化成3个片段，其相对分子质量分别为25、50和21 kDa。只有25 kDa的多肽含有反应性赖氨酸残基。都被抗体染上了。25 kDa的多肽是由25 kDa的多肽和2 kDa的结合肽组成的27 kDa多肽。27 kDa的多肽仅被抗B抗体染色。这一结果表明，A、B头在25k-50k连接附近的结构不同。由于ATPase活性部位位于25 kDa和50 kDa之间，因此A、B头之间的ATPase活性部位结构可能不同。

We prepared antibodies specific to heads A and B of myosin using the difference in the amino-acid sequences of two heads of myosin. We studied whether one myosin molecula has A-B heterodimer structure. It has shown that there exists two defferent heads, A and B.We fixed antibodies thus obtained to protein-A which binds to insoluble materials, and examined whether myosin or S-1 (myosin head) can bind with these antibodies. We found that almost all the myosin added was absorbed by either anti-A or anti-B antibody. Therefore, we concluded that most of the myosin molecule has A-B heterodimer structure. The difference in the chemical structure between heads A and B of the myosin molecule has not yet been elucidated, except the amino-acid sequence around 86th reactive lysine residue. Then, we studied the tryptic digestion of s-1 using antibodies specific to two heads. When S-1 was digested by trypsin myosin heavy chain (100 kDa) was digested into three fragments with molecular masses of 25,50, and 21 kDa. Only 25 kDa peptide which contain the reactive lysine residue. was stained by the antibodies. The 25 kDa peptide was formed via 27 kDa peptide, which is the complex of 25 KDa peptidew and 2 kDa junction peptide. The 27 kDa peptide was stained only by anti-B antibodies. This result suggested that the structure around 25 k-50 k junction differs between heads A and B.Since the ATPase active site was located between the domains of 25 kDa and 50 kDa, the structure of ATPase active site may differs between heads A and B.