Cyclic electron transfer around Photosystem I mediated by 2,3-dichloro-1,4-naphtoquinone and ascorbate.

In this work, we investigated electron transport around the photosynthetic pigment-protein complex of Photosystem I (PS I) mediated by external high-potential electron carrier 2,3-dichloro-1,4-naphtoquinone (Cl NQ) and ascorbate. It has been demonstrated that the oxidized species of Cl NQ and ascorbate serve as intermediates capable of accepting electrons from the iron-sulfur cluster F of PS I. Reduced species of Cl NQ and ascorbate are oxidized by photooxidized PS I primary donor P700+ and/or by molecular oxygen.

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).