COOPERATIVE BINDING OF MYOSIN SUBFRAGMENT-1 TO THE ACTIN-TROPONIN-TROPOMYOSIN COMPLEX
COOPERATIVE BINDING OF MYOSIN SUBFRAGMENT-1 TO THE ACTIN-TROPONIN-TROPOMYOSIN COMPLEX
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DOI：
10.1073/pnas.77.5.2616
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发表时间：
1980-01-01
期刊：
影响因子：
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通讯作者：
EISENBERG, E
中科院分区：
文献类型：
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作者：
GREENE, LE;EISENBERG, E
在ADP（离子强度，0.23 M; 22 ° C）存在下检测兔肌球蛋白亚片段-1（S-1）与F-肌动蛋白-肌钙蛋白-原肌球蛋白复合物（调节的F-肌动蛋白）的结合。C）通过使用超浓缩物和用碘[14 C]乙酰胺在SH 1处封闭的S-1。S-1·ADP在Ca存在和不存在的情况下都以正协同性结合到受调节的F-肌动蛋白;它独立地结合到未受调节的肌动蛋白。在有和没有Ca 2+的情况下，在S-1·ADP对受调节的肌动蛋白的占有率非常低的水平下，S-1·ADP与受调节的肌动蛋白的结合强度小于S-1·ADP与未受调节的肌动蛋白的结合强度的1%，S-1·ADP与受调节的肌动蛋白的结合强度比与未受调节的肌动蛋白的结合强度强约3倍。在存在和不存在Ca 2+的情况下获得的结果与调节的肌动蛋白之间的主要差异在于，在不存在Ca 2+的情况下，S-1·ADP的结合保持弱，直到达到更高的游离S-1·ADP浓度，并且向强结合的转变更加协同。这些结果与Hill的合作结合模型基本相似的模型是一致的。受调节的肌动蛋白丝可以以两种形式存在，弱结合和强结合形式;并且作为变构效应物的Ca 2+和S-1·ADP改变两种形式之间的平衡。
The binding of rabbit myosin subfragment-1 (S-1) to the F-actin-troponin-tropomyosin complex (regulated F-actin) was examined in the presence of ADP (ionic strength, 0.23 M; 22.degree. C) by using the ultracentrifuge and S-1 blocked at SH1 with iodo[14C]acetamide. S-1.cntdot.ADP binds with positive cooperativity to regulated F-actin, both in the presence and absence of Ca; it binds independently to unregulated actin. With and without Ca2+ at very low levels of occupancy of the regulated actin by S-1.cntdot.ADP, S-1.cntdot.ADP binds to the regulated actin with < 1% of the strength that it binds to unregulated actin by S-1.cntdot.ADP, S-1.cntdot.ADP binds about 3-fold more strongly to the regulated actin than it does to unregulated actin. The major difference between the results obtained in the presence and absence of Ca2+ with regulated actin is that, in the absence of Ca2+, the binding of S-1.cntdot.ADP remains weak until a higher free S-1.cntdot.ADP concentration is reached and the transition to strong binding is much more cooperative. These results are consistent with a model that is basically similar to the cooperative binding model of Hill. The regulated actin filament can exist in 2 forms, a weak-binding and a strong-binding form; and Ca2+ and S-1.cntdot.ADP, acting as allosteric effectors, shift the equilibrium between the 2 forms.