Phototrapping of Mono- and Di- Anionic Bacteriopheophytin in the Photoreaction Center of Ectothiorhodospira sp.

Abstract

The photoreductive trapping method (1–3) was used to study electron transfer reactions of the primary electron donor, P, in the photoreaction center of Ectothiorhodospira sp. This photoreaction center contains a tightly bound c-type (four heme) cytochrome (4) which can reduce P⁺ before it undergoes charge recombination with the reduced primary acceptor. By holding the preparation at low redox potential to insure reduction of the quinones, intermediary reduced acceptors can be photo-trapped. If the lifetime of the trapped state is very long compared with its trapping time, continuous illumination can lead to its trapping in large amounts. The photochemical trapping technique can detect acceptors which are reduced by P with very low quantum yields. Using this method, we found that P can transfer electrons to both bacteriopheophytin molecules (BPh) which can accept either one or two electrons.