Initial electron-transfer in the reaction center from Rhodobacter sphaeroides

The initial electron transfer steps in the photosynthetic reaction
center of the purple bacterium Rhodobacter sphaeroides have been
investigated by femtosecond time-resolved spectroscopy. The
experimental data taken at various wavelengths demonstrate the
existence of at least four intermediate states within the first
nanosecond. The difference spectra of the intermediates and
transient photodichroism data are fully consistent with a
sequential four-step model of the primary electron transfer: Light
absorption by the special pair P leads to the state P*. From the
excited primary donor P*, the electron is transferred within 3.5
+/- 0.4 ps to the accessory bacteriochlorophyll B. State P+B-
decays with a time constant of 0.9 +/- 0.3 ps passing the electron
to the bacteriopheophytin H. Finally, the electron is transferred
from H- to the quinone QA within 220 +/- 40 ps.