Abstract
In this theoretical work, we analyse the kinetics of charge recombination reaction after a light excitation of the Reaction Centres extracted from the photosynthetic bacterium Rhodobacter sphaeroides and reconstituted in small unilamellar phospholipid vesicles. Due to the compartmentalized nature of liposomes, vesicles may exhibit a random distribution of both ubiquinone molecules and the Reaction Centre protein complexes that can produce significant differences on the local concentrations from the average expected values. Moreover, since the amount of reacting species is very low in compartmentalized lipid systems the stochastic approach is more suitable to unveil deviations of the average time behaviour of vesicles from the deterministic time evolution.
Highlights
The bacterial photosynthetic Reaction Centre (RC) is a transmembrane pigment-protein complex [1,2,3], that, upon photoexcitation, generates a charge-separated state among a bacteriochlorophyll dimer: the primary donor (D) and two ubiquinone-10 complexes (Q) located in two protein sites indicated as QA and QB, respectively [4].The electron is reversibly exchanged between the two ubiquinones with a thermodynamic constant, named LAB, whose magnitude is related to the stability of Q− in the site QB respect to the stability in the site QA
The charge recombination kinetics of photo-excited reaction centres reconstituted in lipid vesicles have been analysed with two complementary approaches
The first one, the deterministic approach, is based on the numerical solution of the ordinary differential equations (ODE) set associated to the charge recombination (CR) kinetic mechanism
Summary
The bacterial photosynthetic Reaction Centre (RC) is a transmembrane pigment-protein complex [1,2,3], that, upon photoexcitation, generates a charge-separated state among a bacteriochlorophyll dimer: the primary donor (D) and two ubiquinone-10 complexes (Q) located in two protein sites indicated as QA (the primary acceptor) and QB (the secondary acceptor), respectively [4]. Following the deterministic approach and using the experimental POPC decay curves already published by our group [11], this work focuses the attention on how stochastic effects can influence the average time behaviour of a vesicle population determining significant displacements from the deterministic CR time course. This will be done performing Monte Carlo simulations that allow to calculate the CR reaction curves averaging the stochastic behaviour of a large number of single vesicles, using a software platform [21] that implements the Gillespie’s stochastic simulation algorithm [22,23]. Different examples of Monte Carlo methods for the simulation of stochastic kinetics of chemically reacting systems have been reported in earlier works [24,25]
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