The absence of a spectroscopically resolved intermediate state P+Bin bacterial photosynthesis

Abstract
Reaction centers from the photosynthetic bacteriumRhodopseudomonas sphaeroideshave been excited either in the bacteriopheophytin band at 760 nm or in the accessory bacteriochlorophyll (B) band around 800 nm with laser pulses of 150 fs duration. Upon monitoring in the absorption band of the primary donor (P) at 860 nm, ultrafast energy transfer is observed which leads to the excited state of P in less than 100 fs. A transient bleaching recovering in 400 ± 100 fs is specifically detected upon excitation and observation in the 800 nm absorption band of B. However, upon direct excitation of P in the near infrared and using either normal or borohydride‐treated reaction centers, we have found no spectral or kinetic evidence indicating the presence of a transient intermediate state such as P+B.

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