Mathematical model of thylakoid as the distributed heterogeneous system of electron and proton transport

A mathematical model is constructed of the thylakoid functioning as the spatially non-homogeneous system with uneven distribution of the electron transporting and ATP-synthase complexes in lateral direction of the thylacoid membrane. Photosystem I, photosystem II, the b/f-complex are considered as the structural functioning elements; along the thylakoid membrane the interaction between them is realized by plastoquinone diffusion and in the thylakoid lumen by - plastocyanine. The considered proton transporting processes include the proton transfer and lateral diffusion of H⁺ ions in intrathylakoid lumen and the narrow gap of the interthylakoid grana space. The results of numerical calculations agree with some experimental data on the kinetics of the electron and proton transport in chloroplasts, and also show the possibility of the existante of non-homogeneous profiles of the mobile electron carriers distribution (plastoquinone and plastocyanine) and the transmembrane pH difference in the lateral direction of thylacoids. It is shown that the velosity of the electron transport between photosystems may be controlled not only by the value of pH_in in thylakoid at the stage of plastoquinol oxidation, but also at stage of plastoquinone protonation. The limited velosity of diffusiop of H⁺ ions from stroma to the acceptors of photosystem II, those are located in the central part of the thylakoid grana, restricts the plastoquinol protonation and the frequency of the photosystem II functioning.