Interaction of various types of photosystem I complexes with exogenous electron acceptors.

Interaction of photosystem I (PS I) complexes from cyanobacteria Synechocystis sp. PCC 6803 containing various quinones in the A-site (phylloquinone PhQ in the wild-type strain (WT), and plastoquinone PQ or 2,3-dichloronaphthoquinone Cl NQ in the menB deletion strain) and different numbers of FeS clusters (intact WT and F-core complexes depleted of F/F centers) with external acceptors has been studied. The efficiency of interaction was estimated by measuring the light-induced absorption changes at 820 nm due to the reduction of the special pair of chlorophylls (P) by an external acceptor(s). It was shown that externally added Cl NQ is able to effectively accept electrons from the terminal iron-sulfur clusters of PS I. Moreover, the efficiency of Cl NQ as external acceptor was higher than the efficiency of the commonly used artificial electron acceptor, methylviologen (MV) for both the intact WT PS I and for the F-core complexes. The comparison of the efficiency of MV interaction with different types of PS I complexes revealed gradual decrease in the following order: intact WT > menB > F-core. The effect of MV on the recombination kinetics in menB complexes of PS I with Cl NQ in the A-site differed significantly from all other PS I samples. The obtained effects are considered in terms of kinetic efficiency of electron acceptors in relation to thermodynamic and structural characteristics of PS I complexes.