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

Abstract

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 (Cl2NQ) and ascorbate. It has been demonstrated that the oxidized species of Cl2NQ and ascorbate serve as intermediates capable of accepting electrons from the iron–sulfur cluster FX of PS I. Reduced species of Cl2NQ and ascorbate are oxidized by photooxidized PS I primary donor P700+ and/or by molecular oxygen. We have found the synergistic effect of Cl2NQ and ascorbate on the rate of P700+ reduction. Accelerated electron flow to P700+, observed in the presence of both Cl2NQ and ascorbate, is explained by an increase in the reduced species of Cl2NQ due to electron transfer from ascorbate.