Modeling the Q-cycle mechanism of transmembrane energy conversion

TL;DR

This paper presents a kinetic model of the Q-cycle mechanism in an artificial system, demonstrating efficient proton translocation and energy conversion similar to natural bioenergetic processes.

Contribution

It introduces a novel kinetic model of the Q-cycle in an artificial system, revealing conditions for natural electron bifurcation and high proton translocation efficiency.

Findings

Translocates over 1.8 protons per electron on average

Achieves thermodynamic efficiency of around 32% or higher

Identifies energetic conditions for natural electron pathway bifurcation

Abstract

The Q-cycle mechanism plays an important role in the conversion of the redox energy into the energy of the proton electrochemical gradient across the biomembrane. The bifurcated electron transfer reaction, which is built into this mechanism, recycles one electron, thus, allowing to translocate two protons per one electron moving to the high-potential redox chain. We study a kinetic model of the Q-cycle mechanism in an artificial system which mimics the bf complex of plants and cyanobacteria in the regime of ferredoxin-dependent cyclic electron flow. Using methods of condensed matter physics, we derive a set of master equations and describe a time sequence of electron and proton transfer reactions in the complex. We find energetic conditions when the bifurcation of the electron pathways at the positive side of the membrane occurs naturally, without any additional gates. For reasonable parameter values, we show that this system is able to translocate more than 1.8 protons, on average, per one electron, with a thermodynamic efficiency of the order of 32% or higher.