Department of Applied Physics, Tokyo University of Agriculture and Technology, Koganeishi, Tokyo184-8588, Japan.
Biochem Biophys Res Commun. 2011 Feb 25;405(4):651-6. doi: 10.1016/j.bbrc.2011.01.087. Epub 2011 Jan 31.
Muscle contraction results from an attachment-detachment cycle between the myosin heads extending from myosin filaments and the sites on actin filaments. The myosin head first attaches to actin together with the products of ATP hydrolysis, performs a power stroke associated with release of hydrolysis products, and detaches from actin upon binding with new ATP. The detached myosin head then hydrolyses ATP, and performs a recovery stroke to restore its initial position. The strokes have been suggested to result from rotation of the lever arm domain around the converter domain, while the catalytic domain remains rigid. To ascertain the validity of the lever arm hypothesis in muscle, we recorded ATP-induced movement at different regions within individual myosin heads in hydrated myosin filaments, using the gas environmental chamber attached to the electron microscope. The myosin head were position-marked with gold particles using three different site-directed antibodies. The amplitude of ATP-induced movement at the actin binding site in the catalytic domain was similar to that at the boundary between the catalytic and converter domains, but was definitely larger than that at the regulatory light chain in the lever arm domain. These results are consistent with the myosin head lever arm mechanism in muscle contraction if some assumptions are made.
肌肉收缩是由肌球蛋白丝上伸出的肌球蛋白头部与肌动蛋白丝上的结合位点之间的附着-脱离循环引起的。肌球蛋白头部首先与肌动蛋白一起结合 ATP 水解产物，进行与水解产物释放相关的力作用冲程，并在与新的 ATP 结合后脱离肌动蛋白。然后，脱离的肌球蛋白头部水解 ATP，并进行恢复冲程以恢复其初始位置。已经提出这些冲程是由杠杆臂结构域围绕转换器结构域的旋转引起的，而催化结构域保持刚性。为了确定肌肉中杠杆臂假说的有效性，我们使用附着在电子显微镜上的气体环境室，在水合肌球蛋白丝中记录单个肌球蛋白头部内不同区域的 ATP 诱导运动。使用三种不同的定点抗体用金颗粒标记肌球蛋白头部。在催化结构域的肌动蛋白结合位点处的 ATP 诱导运动的幅度与在催化和转换器结构域之间的边界处的幅度相似，但明显大于在杠杆臂结构域中的调节轻链处的幅度。如果做出一些假设，这些结果与肌肉收缩中的肌球蛋白头部杠杆臂机制一致。
