Primary Charge Separation Between P700* and the Primary Electron Acceptor Complex A-A0: A Comparison with Bacterial Reaction Centers

Abstract

The mechanism of charge separation and the stabilization of separated charges in photosystem I (PS I) is considered in comparison with reaction centers (RCs) in bacteria. The analysis of the X-ray crystal structures of the RCs together with psec and fsec studies of charge separation coupled to nuclear motion in the system provides new insight into the problem. A psec study of PS I RCs has shown that the primary charge separation takes place between P700∗ and the A-A0 complex. The three-dimensional structure of both the primary electron donor and acceptor shows a possible pathway for electron transfer between P700 and the A-A0 complex that is governed by nuclear motions. A fsec study of a coherent formation of the nuclear wavepacket on the potential energy surface of the excited state of the primary electron donor P∗ and of the charge separated state P+A− (where A is the primary electron acceptor) in native, pheophytin-modified and mutant reaction centers of Rhodobacter spaeroides was compared with X-ray and psec data for PS I RCs. A mechanism of the charge separation and stabilization of separated charges in PS I RCs is proposed.