An assessment of the mechanism of initial electron transfer in bacterial reaction centers.

Subpicosecond time-resolved photodichroism measurements on Rhodobacter sphaeroides R26 reaction centers are reported in the key region between 620 and 740 nm, where the anions of both bacteriopheophytin and bacteriochlorophyll (BChl) have their most diagnostic absorption bands. These measurements fail to resolve clearly the formation of a reduced BChl species. The implications of this for elucidating the role of the accessory BChl in the initial stage of charge separation are discussed.