[Electron transport and transmembrane proton transfer in photosynthetic systems of oxygenic type in silico]

In this work, using a mathematical model of light-induced stages of photosynthesis, taking into account the key stages of pH-dependent regulation on the acceptor and donor sides of PS1, we analyzed electron and proton transport in chloroplasts of higher plants and cyanobacterial cells. A comparison of computer simulation results with experimental data showed that our model adequately described a complex non-monotonous kinetics of the light-induced redox transients of P700. Effects of atmospheric gases (CO2 and O2) on the kinetics of photooxidation of P700 and generation of the transmembrane pH difference were studied. We also analyzed how cyclic electron transport influenced the kinetics of electron transfer, the intrathylakoid pH, and ATP production. Within the framework of our model, we described the time-courses of electron flow through PS2 and distribution of electron fluxes on the acceptor side of PS1 in chloroplasts of higher plants and in cyanobacterial cells. It was demonstrated that contributions of cyclic electron transport and electron flow to O2 (the Mehler reaction) were significant during the initial phase of the induction period, but diminished upon the activation of the Calvin-Benson cycle.