Wegner A, Engel J
Biophys Chem. 1975 Jul;3(3):215-25. doi: 10.1016/0301-4622(75)80013-5.
The cooperative formation of actin filaments from monomers was followed by light scattering and electron microscopy. The results are well described by a simple model mechanism in which the growth and destruction of filaments occurs by stepwise addition or dissociation of protomers. All steps except the dimerisation step are assumed to have identical rate constants. These were found to be 5 X 10(3) M-1 - sec-1 and 3 X 10(-2) sec-1 for the association and dissociation, respectively (at pH 7.5 and in the presence of 10(-3) M calcium chloride). The equilibrium constant of elongation as obtained from the critical concentration is 1.7 X 10(5) M-1. The corresponding equilibrium constant of dimerisation is about 10 million times smaller (cooperativity parameter sigma = 2 X 10(-7)). This makes the nucleation extremely difficult and cooperativity very high. A best fit of the model to the experimental data is achieved when the destruction of a dimer is much faster than the addition of a third protomer (fast monomer- dimer pre-equilibrium). The size of the nucleus from which propagation becomes faster than dissociation is 3.
通过光散射和电子显微镜观察肌动蛋白单体协同形成丝的过程。一个简单的模型机制能很好地描述这些结果，在该模型中，丝的生长和破坏通过原聚体的逐步添加或解离发生。除二聚化步骤外，所有步骤的速率常数都假定相同。在pH 7.5且存在10⁻³ M氯化钙的条件下，发现缔合和解离的速率常数分别为5×10³ M⁻¹·s⁻¹和3×10⁻² s⁻¹。从临界浓度获得的伸长平衡常数为1.7×10⁵ M⁻¹。相应的二聚化平衡常数约小1000万倍（协同参数σ = 2×10⁻⁷）。这使得成核极其困难且协同性非常高。当二聚体的破坏比第三个原聚体的添加快得多（快速单体 - 二聚体预平衡）时，该模型与实验数据能实现最佳拟合。传播速度快于解离的核的大小为3。
