Du J, Frieden C
Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, Saint Louis, Missouri 63110, USA.
Biochemistry. 1998 Sep 22;37(38):13276-84. doi: 10.1021/bi981117r.
The effect of yeast cofilin on the kinetics of polymerization of yeast actin has been examined at 20 degrees C at both pH 8.0 and 6.6. In the absence of cofilin, the kinetic data may be described by a simple nucleation-elongation mechanism. Kinetic data in the presence of cofilin suggests a complex dependence on the cofilin concentration. At low cofilin-to-actin ratios, cofilin increases the rate of polymerization in a way best fit by assuming filament fragmentation. The apparent fragmentation rate constants increase with increasing cofilin concentration leveling off above a cofilin-to-actin ratio of 1:8 and are independent of pH. At higher cofilin-to-actin ratios, a nonpolymerizable cofilin-G-actin complex forms resulting in a decreased rate of polymerization. The data from fluorescence photobleaching recovery experiments at low cofilin-to-actin ratios are consistent with the presence of severed filaments at both pH 8 and 6.6. However, at pH 8 and a cofilin-to-actin ratio of 1:16, about 40-50% of the total actin is present as G-actin after polymerization while at pH 6.6 little or no G-actin is present at the same cofilin-to-actin ratio. The results suggest some cooperativity with respect to cofilin binding to filamentous actin which may be pH dependent.
已在20摄氏度、pH 8.0和pH 6.6条件下研究了酵母丝切蛋白对酵母肌动蛋白聚合动力学的影响。在没有丝切蛋白的情况下，动力学数据可用简单的成核-延伸机制来描述。存在丝切蛋白时的动力学数据表明其对丝切蛋白浓度有复杂的依赖性。在低丝切蛋白与肌动蛋白比例下，丝切蛋白以假定的丝状肌动蛋白片段化方式最佳拟合的方式增加聚合速率。表观片段化速率常数随丝切蛋白浓度增加而增加，在丝切蛋白与肌动蛋白比例高于1:8时趋于平稳，且与pH无关。在较高的丝切蛋白与肌动蛋白比例下，形成不可聚合的丝切蛋白-G-肌动蛋白复合物，导致聚合速率降低。低丝切蛋白与肌动蛋白比例下荧光光漂白恢复实验的数据与pH 8和pH 6.6时均存在切断的丝状肌动蛋白一致。然而，在pH 8、丝切蛋白与肌动蛋白比例为1:16时，聚合后约40%-50%的总肌动蛋白以G-肌动蛋白形式存在，而在pH 6.6、相同丝切蛋白与肌动蛋白比例下几乎没有或不存在G-肌动蛋白。结果表明丝切蛋白与丝状肌动蛋白结合存在某种协同性，这可能依赖于pH。
