Taniguchi M
Biochim Biophys Acta. 1976 Mar 18;427(1):126-40. doi: 10.1016/0005-2795(76)90291-9.
Asakura, Taniguchi and Oosawa [1]proposed that muscle actin polymer under sonic vibration is in a different state from that of the ordinary double stranded helical structure (F-actin), characterised by partially interrupted structures of F-actin, a state of "f-actin". In order to confirm different states for actin polymers [1, 2], physicochemical studies were made by measurements of viscosity, flow birefringence, electric birefringence, fluorescence, electron microscopy, quasielastic light scattering and ATP splitting. The following results were obtained. (1) F-actin polymers can undergo two processes of depolymerization upon treatment with urea and various salts as judged by measurements of flow birefringence and viscosity: one is a rapid process in a solution containing K+ or Ca2+ and urea; the other is a slow process following a brief rapid one in a solution containing Mg2+ and urea. (2) In the presence of Mg2+ and a suitable concentration of urea, F-actin (FMU-actin) appeared to exhibit different properties than ordinary F-actin; it had lower viscosity and lower flow birefringence and it had on the whole a more flexible polymer structure, also judging from experiments of quasielastic light scattering, electric birefringence. The different structure was confirmed directly be electron microscopic observation. The aromatic side chains of FMU-actin were also more mobile than those of F-actin judging from fluorescence measurements. The transformation between F-actin and FMU-actin was reversible. (3) The state of FMU-actin polymers was also characterized by ATP splitting; FMU-actin split about one mole of ATP into ADP and inorganic phosphate per mole of actin monomer at room temperature, where F-actin did not. A molar excess of Mg2+ with respect to actin monomer at room temperature, where F-actin did not. A molar excess of Mg2+ with respect to actin monomer is required for ATP splitting. F-actin in solutions containing K+ or Ca2+ and urea did not split ATP. FMU-actin activated on Mg-ATP-ase of myosin at nearly the same rate as that of F-actin. (4) We have postulated a flexible filament model (f-actin). The relationships between the structure of f-actin and its functional role for force generation during contraction are discussed.
朝仓、谷口和大泽[1]提出，在声波振动下肌肉肌动蛋白聚合物处于与普通双链螺旋结构（F-肌动蛋白）不同的状态，其特征是F-肌动蛋白结构部分中断，即“f-肌动蛋白”状态。为了证实肌动蛋白聚合物的不同状态[1,2]，通过测量粘度、流动双折射、电双折射、荧光、电子显微镜、准弹性光散射和ATP分解进行了物理化学研究。得到了以下结果。（1） 通过测量流动双折射和粘度判断，F-肌动蛋白聚合物在用尿素和各种盐处理时可经历两个解聚过程：一个是在含有K+或Ca2+和尿素的溶液中的快速过程；另一个是在含有Mg2+和尿素的溶液中短暂快速过程后的缓慢过程。（2） 在Mg2+和合适浓度尿素存在下，F-肌动蛋白（FMU-肌动蛋白）似乎表现出与普通F-肌动蛋白不同的性质；它具有较低的粘度和较低的流动双折射，并且从准弹性光散射、电双折射实验判断，其聚合物结构总体上更灵活。通过电子显微镜观察直接证实了不同的结构。从荧光测量判断，FMU-肌动蛋白的芳香侧链也比F-肌动蛋白的更具流动性。F-肌动蛋白和FMU-肌动蛋白之间的转变是可逆的。（3） FMU-肌动蛋白聚合物的状态还以ATP分解为特征；在室温下，每摩尔肌动蛋白单体FMU-肌动蛋白将约一摩尔ATP分解为ADP和无机磷酸盐，而F-肌动蛋白则不会。室温下相对于肌动蛋白单体需要摩尔过量的Mg2+才能进行ATP分解。含有K+或Ca2+和尿素的溶液中的F-肌动蛋白不会分解ATP。FMU-肌动蛋白激活肌球蛋白的Mg-ATP酶的速率与F-肌动蛋白几乎相同。（4） 我们提出了一个柔性细丝模型（f-肌动蛋白）。讨论了f-肌动蛋白的结构与其在收缩过程中产生力的功能作用之间的关系。
