Hasegawa T, Takahashi S, Hayashi H, Hatano S
Biochemistry. 1980 Jun 10;19(12):2677-83. doi: 10.1021/bi00553a021.
Physarum actinin previously isolated [Hatano, S., & Owaribe, K. (1976) in Cell Motility (Goldman, R., Pollard, T., & Rosenbaum, J., Eds.) Vol. 3, Book B, p 499, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY] was found to be a 1:1 complex of actin and fragmin which is a regulatory factor in the formation of actin filaments. Since fragmin did not contain a cysteine residue, it was purified from the complex by the selective cleavage of actin with 2-nitro-5-thiocyanobenzoic acid, followed by column chromatography. Fragmin had nearly the same molecular weight as actin, but had a quite different amino acid composition. When added to G-actin before polymerization, fragmin accelerated the initial viscosity increase of actin solutions induced by salts, but kept the final viscosity much lower than normal F-actin. When added to F-actin after polymerization, fragmin drastically reduced the viscosity of actin solutions. In both cases, the final products of reaction of fragmin with actin were short F-actin filaments. The number average length of the filaments decreased with the increasing molar ratio of fragmin to actin, and the length distribution was always exponential. Fragmin required for its activity a concentration of free Ca2+ higher than 10(-6) M. When the concentration of free Ca2+ was lower than 10(-7) M, fragmin affected neither actin polymerization nor F-actin. The regulation by Ca2+ was reversible.
此前分离得到的多头绒泡菌肌动蛋白结合蛋白[波多野，S.，及小针，K.（1976年），载于《细胞运动》（戈德曼，R.，波拉德，T.，及罗森鲍姆，J.编）第3卷，B册，第499页，冷泉港实验室，纽约冷泉港]被发现是肌动蛋白与凝溶胶蛋白的1:1复合物，而凝溶胶蛋白是肌动蛋白丝形成过程中的一种调节因子。由于凝溶胶蛋白不含半胱氨酸残基，通过用2-硝基-5-硫氰基苯甲酸选择性切割肌动蛋白，随后进行柱色谱法，从复合物中纯化出了凝溶胶蛋白。凝溶胶蛋白的分子量与肌动蛋白相近，但氨基酸组成却大不相同。在聚合前添加到G-肌动蛋白中时，凝溶胶蛋白加速了盐诱导的肌动蛋白溶液初始黏度的增加，但使最终黏度远低于正常的F-肌动蛋白。在聚合后添加到F-肌动蛋白中时，凝溶胶蛋白显著降低了肌动蛋白溶液的黏度。在这两种情况下，凝溶胶蛋白与肌动蛋白反应的最终产物都是短的F-肌动蛋白丝。丝的数均长度随凝溶胶蛋白与肌动蛋白摩尔比的增加而减小，且长度分布始终呈指数形式。凝溶胶蛋白发挥活性所需的游离Ca2+浓度高于10^(-6) M。当游离Ca2+浓度低于10^(-7) M时，凝溶胶蛋白对肌动蛋白聚合和F-肌动蛋白均无影响。Ca2+的调节是可逆的。
