Catalytic Wheel as a Brownian Motor

Abstract

A system is considered in which transitions between two states occur through two reaction channels. Because of coupling with an external process which consists of cyclic switching between two regimes (each characterized by a certain fixed set of rate constants), the net circulation flux arises in the system even in the absence of an external generalized force. Such a mechanism underlying a catalytic wheel of many biological processes is considered as a Brownian motor. The basic operational motor characteristics are calculated for the regular and random inter-regime switching, being better in the former case and reaching the optimum at equal relaxation-to-lifetime ratios for the two regimes. The general Brownian motor formalism is exemplified by two particular realizations, the electroconformational-coupling model and the flashing-potential model. The former concerns enzymatically catalyzed ligand pumping through a membrane, and the latter describes particle motion under two sets of potential wells and barriers. Because of a unified thread between the two models, their parameters are interrelated, and all of the relevant conclusions are valid for either of them. In the tight coupling limit, the optimal conditions are analyzed, and they imply that a catalytic wheel operated by the Brownian motor works with the maximum output energy (useful work) or with the maximum efficiency tending to unity under certain conditions.

Adaptive machine and its thermodynamic costs

“…Also, we reproduce the conclusions of 1-4 by keeping the dependence of τ k on ∆Q. Note that the changes in (22) should respect the linear regime:…”

“…If our machine is supposed to work in such an uncertain environment, the only possibility to ensure its optimal functioning is to assume that its structure S changes and adjusts the energy difference to ∆E =μ ′ after each environmental changeμ →μ ′ ; see (22). Then the current is maximal under each environment.…”

“…To quantify this aspect, we need to specify the statistics of environmental changes. For simplicity we assume that in (22) …”

Molecular pump functioning due to fluctuations of intramembrane potential

“…Кроме того, развитие теории таких наноустройств является необходимым для разработки искусственных молеку-лярных и наноразмерных механизмов, движением ко-торых можно управлять путем подведения к ним энер-гии и информации. На подобном принципе основана электроконформационная модель [6][7][8][9], объясняющая работу молекулярного насоса, управляемого флуктуа-циями электрического поля [10,11]. В работах [12,13] анализировалась упрощенная модель молекулярного насоса, в которой флуктуации потенциала внутри клеточной мембраны могут инициировать движение ионов против их градиента концентраций на границах мембраны или, по крайней мере, препятствовать их движению через мембрану.…”

“…Поток мотора обращается в нуль, тогда как поток насоса экспоненциально увеличивается с увеличением амплитуды потенциала. Отметим, что в этом частном случае броуновская динамика насоса описывается точ-ными аналитическими соотношениями во всей области частот флуктуаций знака потенциала [10]. а б Рис.…”