Optimal efficiency of the Q-cycle mechanism around physiological temperatures from an open quantum systems approach

TL;DR

This paper uses an open quantum systems approach to model the Q-cycle in photosynthesis, demonstrating optimal efficiency at physiological temperatures and providing insights into quantum effects in biological energy transport.

Contribution

It introduces a quantum master equation model for the Q-cycle, revealing optimal efficiency near physiological temperatures and advancing the understanding of quantum effects in biological systems.

Findings

Optimal thermodynamic efficiency of the Q-cycle around ambient temperatures

Quantum yield calculations consistent with biological data

Validation of quantum open systems theory for biological energy transport

Abstract

The Q-cycle mechanism entering the electron and proton transport chain in oxygenic photosynthesis is an example of how biological processes can be efficiently investigated with elementary microscopic models. Here we address the problem of energy transport across the cellular membrane from an open quantum system theoretical perspective. We model the cytochrome $b_6f$ protein complex under cyclic electron flow conditions starting from a simplified kinetic model, which is hereby revisited in terms of a quantum master equation formulation and spin-boson Hamiltonian treatment. We apply this model to theoretically demonstrate an optimal thermodynamic efficiency of the Q-cycle around ambient and physiologically relevant temperature conditions. Furthermore, we determine the quantum yield of this complex biochemical process after setting the electrochemical potentials to values well established in the literature. The present work suggests that the theory of quantum open systems can successfully push forward our theoretical understanding of complex biological systems working close to the quantum/classical boundary.