Fluctuation analysis of motor protein movement and single enzyme kinetics.

We studied fluctuations in the displacement of silica beads driven by single molecules of the motor protein kinesin, moving under low mechanical loads at saturating ATP concentrations. The variance in position was significantly smaller than expected for the case of stepwise movement along a regular lattice of positions with exponentially distributed intervals. The small variance suggests that two or more sequential processes with comparable reaction rates dominate the biochemical cycle. The low value is inconsistent with certain recently proposed thermal ratchet models for motor movement as well as with scenarios where the hydrolysis of a single ATP molecule leads to a cluster of several steps. Fluctuation analysis is a potential powerful tool for studying kinetic behavior whenever the output of a single enzyme can be monitored.

本研究针对三磷酸腺苷（ATP）饱和浓度、低机械负载条件下，由单分子驱动蛋白（kinesin）驱动的二氧化硅微球的位移波动展开了分析。观测得到的位置方差显著低于沿规则位置晶格、以指数分布间隔步进运动时的理论预期值。这种偏低的位置方差提示，两个乃至更多反应速率相近的连续过程主导了该生化循环。该结果与近期提出的若干用于解释马达蛋白运动的热棘轮模型相悖，同时也不符合单个ATP水解即可触发多步步进的相关假说。只要能够监测单个酶的活性输出，波动分析便可成为研究其动力学行为的有力工具。