Modeling of the photosynthetic electron transport regulation in cyanobacteria

Abstract

In this work we have performed a computer analysis of electron and proton transport in cyanobacterial cells using a mathematical model of light-dependent stages of photosynthesis taking into account the key stages of pH-dependent regulation of electron transport on both acceptor and donor sides of photosystem 1 (PS1). Comparison of theoretical and experimental data shows that the model adequately describes the multiphase kinetics of photoinduced redox transformations of P700 (the primary electron donor in PS1). Our computer simulation describes the effect of variations of atmospheric gases (CO2 and O2) on the induction events in cyanobacteria (P700 photooxidation, generation of transmembrane ΔpH), which strongly depends on the preillumination conditions (aerobic or anaerobic atmosphere). It has been shown that the variations of CO2 concentration in the cell interior may noticeably affect the kinetics of electron transport, acidification of lumen, and ATP synthesis. The contributions of alternative pathways of electron transport (cyclic electron transport around PS1 and electron outflow to O2) to the function of cyanobacterial photosynthetic apparatus have been analyzed. At the initial stage of induction period, cyclic electron flows around PS1 (“short” and “long” pathways) substantially contribute to photosynthetic electron transport. These flows, however, attenuate with the light-induced activation of the Calvin-Benson cycle reactions. In the meantime, the outflow of electrons from PS1 to O2 (or to other metabolic chains) increases with oxygen accumulation in the medium. The effects of ferredoxin oxidation by hydrogenase catalyzing the H2 formation on the kinetics of P700 photooxidation and distribution of electron flows on the acceptor side of PS1 have been modeled.