Center for Soft and Living Matter, Institute for Basic Science, Ulsan 44919, Republic of Korea.
Department of Physics, Ulsan National Institute of Science and Technology, Ulsan 44919, Republic of Korea.
Proc Natl Acad Sci U S A. 2020 Nov 24;117(47):29435-29441. doi: 10.1073/pnas.2019810117. Epub 2020 Nov 9.
Molecular agitation more rapid than thermal Brownian motion is reported for cellular environments, motor proteins, synthetic molecular motors, enzymes, and common chemical reactions, yet that chemical activity coupled to molecular motion contrasts with generations of accumulated knowledge about diffusion at equilibrium. To test the limits of this idea, a critical testbed is the mobility of catalytically active enzymes. Sentiment is divided about the reality of enhanced enzyme diffusion, with evidence for and against. Here a master curve shows that the enzyme diffusion coefficient increases in proportion to the energy release rate-the product of Michaelis-Menten reaction rate and Gibbs free energy change ()-with a highly satisfactory correlation coefficient of 0.97. For 10 catalytic enzymes (urease, acetylcholinesterase, seven enzymes from the glucose cascade cycle, and one other), our measurements span from a roughly 40% enhanced diffusion coefficient at a high turnover rate and negative to no enhancement at a slow turnover rate and positive Moreover, two independent measures of mobility show consistency, provided that one avoids undesirable fluorescence photophysics. The master curve presented here quantifies the limits of both ideas, that enzymes display enhanced diffusion and that they do not within instrumental resolution, and has possible implications for understanding enzyme mobility in cellular environments. The striking linear dependence of Δ for the exergonic enzymes (Δ <0), together with the vanishing effect for endergonic enzyme (Δ >0), are consistent with a physical picture in which the mechanism boosting the diffusion is an active one, utilizing the available work from the chemical reaction.
据报道,在细胞环境、马达蛋白、合成分子马达、酶和常见化学反应中,分子的搅动比热布朗运动快,然而,这种与分子运动相耦合的化学活性与几代人积累的关于平衡扩散的知识相矛盾。为了检验这一观点的极限,一个关键的试验台是催化活性酶的流动性。关于增强酶扩散的现实性存在分歧,有支持和反对的证据。这里的一条主曲线表明,酶的扩散系数与能量释放率成正比,即米氏-门坦反应速率和吉布斯自由能变化的产物(),相关系数高达 0.97。对于 10 种催化酶(脲酶、乙酰胆碱酯酶、葡萄糖级联循环中的 7 种酶和另一种酶),我们的测量结果跨越了从高周转率和负到低周转率和正的大约 40%的增强扩散系数。此外,两种独立的流动性测量方法具有一致性,前提是避免不希望的荧光光物理。这里提出的主曲线量化了酶显示增强扩散和在仪器分辨率内没有增强扩散的极限的两个想法,并可能对理解细胞环境中酶的流动性具有意义。对于放能酶(Δ<0),Δ的显著线性依赖性,以及对于吸能酶(Δ>0)的消失效应,与一种物理图景一致,即促进扩散的机制是一种主动机制,利用化学反应中可用的功。