Trapping the P+B(L)- initial intermediate state of charge separation in photosynthetic reaction centers from Rhodobacter capsulatus.

The short-lived (<1 ps) initial intermediate state P(+)B(L)(-) in the photoinduced charge separation process of the bacterial photosynthetic reaction center has been trapped in two D(LL)-based Rhodobacter capsulatus mutants that have Tyr at position M208 and lack the bacteriopheophytin electron acceptor H(L). Transient state P(+)B(L)(-) is characterized by a 1017 nm bacteriochlorophyll anion absorption band and decays by charge recombination with a lifetime of several hundred picoseconds at 295 K. P(+)B(L)(-) is not observed in an otherwise identical mutant that has Phe at M208, which appears to make the state thermodynamically inaccessible from the excited primary electron donor P*.