Kinetics of Charge Separation and A0 - → A1 Electron Transfer in Photosystem I Reaction Centers

• Published in: Biochemistry (Easton) 2001-08, Vol.40 (31), p.9282-9290
• Main Authors: Savikhin, Sergei, Xu, Wu, Martinsson, Peter, Chitnis, Parag R, Struve, Walter S
• Format: Article
• Language: English
• Subjects: Chlorophyll - metabolism; Computer Simulation; Confidence Intervals; Cyanobacteria - metabolism; Electron Transport; Kinetics; Light-Harvesting Protein Complexes; Models, Chemical; Normal Distribution; Photolysis; Photosynthetic Reaction Center Complex Proteins - metabolism; Photosystem I Protein Complex; Spectrophotometry - methods; Spectrophotometry - statistics & numerical data
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi0104165

The charge separation P700*A0 → P700+A0 - and the subsequent electron transfer from the primary to secondary electron acceptor have been studied by subtracting absorption difference profiles for cyanobacterial photosystem I (PS I) complexes with open and closed reaction centers. Samples were excited at 660 nm, which lies toward the blue edge of the core antenna absorption spectrum. The resulting PS I kinetics were analyzed in terms of the relevant P700, P700+, A0, and A0 - absorption spectra. In our kinetic model, the radical pair P700+A0 - forms with 1.3 ps rise kinetics after creation of electronically excited P700*. The formation of A1 - via electron transfer from A0 - requires ∼13 ps. The kinetics of the latter step are appreciably faster than previously estimated by other groups (20−50 ps).