Diffusion-controlled generation of a proton-motive force across a biomembrane

TL;DR

This paper presents a kinetic model of bacterial respiration that explains how electron and proton transfers generate a proton-motive force across membranes, highlighting the role of electrostatic coupling and efficiency in energy conversion.

Contribution

It introduces a detailed kinetic model of the redox loop mechanism, including multiple binding sites, to analyze proton translocation and efficiency in bacterial respiration.

Findings

Proton translocation can occur against a 200 mV gradient.

The model achieves about 37% thermodynamic efficiency.

Electrostatic coupling significantly influences energy conversion.

Abstract

Respiration in bacteria involves a sequence of energetically-coupled electron and proton transfers creating an electrochemical gradient of protons (a proton-motive force) across the inner bacterial membrane. With a simple kinetic model we analyze a redox loop mechanism of proton-motive force generation mediated by a molecular shuttle diffusing inside the membrane. This model, which includes six electron-binding and two proton-binding sites, reflects the main features of nitrate respiration in E. coli bacteria. We describe the time evolution of the proton translocation process. We find that the electron-proton electrostatic coupling on the shuttle plays a significant role in the process of energy conversion between electron and proton components. We determine the conditions where the redox loop mechanism is able to translocate protons against the transmembrane voltage gradient above 200 mV with a thermodynamic efficiency of about 37%, in the physiologically important range of temperatures from 250 to 350 K.