Effects of Diffusion and Topological Factors on the Efficiency of Energy Coupling in Chloroplasts with Heterogeneous Partitioning of Protein Complexes in Thylakoids of Grana and Stroma. A Mathematical Model

Abstract

In this work, we studied theoretically the effects of diffusion restrictions and topological factors that could influence the efficiency of energy coupling in the heterogeneous lamellar system of higher plant chloroplasts. Our computations are based on a mathematical model for electron and proton transport in chloroplasts coupled to ATP synthesis in chloroplasts that takes into account the nonuniform distribution of electron transport and ATP synthase complexes in the thylakoids of grana and stroma. Numerical experiments allowed the lateral profiles of pH in the thylakoid lumen and in the narrow gap between grana thylakoids to be simulated under different metabolic conditions (in the state of photosynthetic control and under conditions of photophosphorylation). This model also provided an opportunity to simulate the effects of steric constraints (the extent of appression of thylakoids in grana) on the rates of non-cyclic electron transport and ATP synthesis. This model demonstrated that there might be two mechanisms of regulation of electron and proton transport in chloroplasts: 1) slowing down of non-cyclic electron transport due to a decrease in the intra-thylakoid pH, and 2) retardation of plastoquinone reduction due to slow diffusion of protons inside the narrow gap between the thylakoids of grana. Numerical experiments for model systems that differ with respect to the arrangement of thylakoids in grana allowed the effects of osmolarity on the photophosphorylation rate in chloroplasts to be explained.

Influence of Subenvironmental Conditions and Thermodynamic Coupling on a Simple Reaction-Transport Process in Biochemical Systems

“…Eukaryotic cells possess a hierarchy of transport systems to maintain nonequilibrium concentration levels of some substrates within organelles than those in the cell’s cytoplasm. Still, the cell controls its complex array of chemical reaction cycles so that the supply and demand for substrates, energy, and electrons are balanced and resources are utilized efficiently. ,, …”

“…Some processes will not be dependent on some of the forces when some of the cross-coefficients vanish naturally. For example, some degrees of imperfections due to parallel pathways of reaction or intrinsic uncoupling within the pathway itself may lead to leaks and slips in mitochondria. , …”

“…In order to maintain the self-organization and low-entropy structure processes, living systems must continuously receive nutrients from subenvironment. The population metabolic rate model focuses on this flow of nutrients to be metabolized, its relevant variables, and the rate at which operates. − The metabolism takes place due to the combined effects of many functional, synchronized, and thermodynamically coupled transport and rate processes within the system as a whole. Coupled reaction-transport processes are of great importance in biological systems; many biosynthesis processes, such as synthesis of the complex enzyme macromolecules from the amino acids, are nonspontaneous processes made possible by virtue of being coupled with other spontaneous processes such as oxidation of glucose .…”

“…One of the problems in bioenergetics is to understand the ability of complex coupled cycles of metabolism to achieve efficient and functional processes and their adaptation to variable subenvironmental restrictions and topological factors. − ,, A mathematical model is used to analyze the transport of electron and proton thermodynamically coupled to adenosine triphosphate (ATP) synthesis in chloroplast by taking into account the nonuniform distribution of electron transport and ATP synthases complexes in the thylakoid of grana and stroma. For example, the rate of electron transfer at the plastoquinone site of the chain could be controlled not only by the intrathylakoid pH but also by the value of pH in the interthylakoid gap, which affects the rate of plastoquinone reduction . Also, the rate of ATP synthesis depends on osmotic properties of a chloroplast incubation medium and hence on topological conditions.…”

Effects of thermodynamically coupled reaction diffusion in microalgae growth and lipid accumulation: Model development and stability analysis

“…The population metabolic rate model for the biological systems is focused on the flow of nutrients for metabolism, relevant variables, and the rate at which the metabolic rate model operates (Vershubskii et al, 2004;Virgo et al, 2006). The metabolism is a combined effect of many functional, synchronized, and thermodynamically coupled reaction-diffusion (RD) processes.…”