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

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 protein complex under cyclic electron flow conditions starting from a simplified kinetic model, which is hereby revisited in terms of a Markovian 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.

Efficient and reversible electron bifurcation with either normal or inverted potentials at the bifurcating cofactor

“…8,23,32,33 However, the proposed gating mechanisms have not been demonstrated conclusively in cytochromes bc 1 . 10,[22][23][24][34][35][36][37] Recently, a thermodynamic landscape (the reversible EB scheme) was discovered that robustly insulates near-reversible electron bifurcating enzymes from short-circuiting, enabling an efficient and reversible electron bifurcation 10 (the reverse process is known as electron confurcation), illustrated in Figure 1B. The redox landscapes of the high-and low-potential branches in the EB scheme have steep redox-potential gradients that are much greater than the thermal energy.…”

“…The kinetics of electron bifurcating systems is rich. Proton-coupled electron transfer, 9,44 conformational movement, 50,57,58 and transmembrane particle motion 23,37 may all be coupled to electron bifurcation and add potential complexity. While our model does not explore any of these specific features in molecular detail, we suggest that the rate constants used in our model are typical, 59 and that many of the emergent kinetic features are generic.…”

Quantum dissipative adaptation

“…As a consequence of our work, we establish the starting point of a quantum thermodynamics of driven self-organization, so far unexplored to the best of our knowledge. We hope that the notion of a quantum dissipative adaptation may also provide fresh insights to quantum biology 16 , not only because adaptation and self-organization are concepts inspired in life-like behavior, but also because our results may find applications to discussions on quantum signatures in photosynthesis [17][18][19][20] .…”

Molecular mechanisms underlying the renal protective effects of coenzyme Q10 in acute kidney injury

“…CoQ10 appears generally in two forms: reduced (ubiquinol) and oxidized (ubiquinone) [ 32 ]. Both coexist and regenerate each other via sequential redox reactions (Q cycle) [ 33 ]. Ubiquinol shows antioxidant behaviors in cell and organelle membranes, reducing oxidative stress and lipid peroxidation and regenerating vitamins C and E back to their active form [ 29 ].…”