ABSTRACT
My motivation to study biophysics was the question of how physics can explain the emergence, existence, and evolution of life. Photosynthesis is essential for the present-day living world. The initial irreversible steps convert photon's free energy and redox energy into the electrochemical potential difference of protons (the protonmotive force). The dissipation is associated with the photocycle turnover and also with each transitional step. We derived the proof that maximal entropy production can be found for each transition between enzyme functional states. The MaxEP requirement for the productive charge-separating transitions in the driven cycle produced the optimal efficiency and the optimal value for the recovery rate constant. These values were in good agreement with measurements for the bacteriorhodopsin and Rhodobacter sphaeroides photocycle. We considered the physiological steady state when a large enough protonmotive force of about 0.2 V is established to drive the ATP-synthesis. About 80% of the photon's free-energy is then dissipated as heat, while optimal transduction efficiency is about 20%. We proposed that a productive charge-separation pathway was optimized during biological evolution for maximal contribution to corresponding entropy production steps and modest free-energy transduction efficiency because it led both to the biological gain of optimal power transfer and the increased entropy gain for the universe. This proposal brings biological evolution in complete synergy with thermodynamic evolution: the former accelerates the latter.
