Charge Separation In Bacterial Reaction Centers Research Articles

Primary processes in bacterial reaction center revealed by femtosecond broadband fluorescence spectroscopy

To gain a deeper understanding of the highly efficient mechanisms within the photosynthetic bacterial reaction center (BRC), we have employed femtosecond broadband fluorescence spectroscopy to investigate the dynamics of initial photo-induced energy transfer and charge separation in BRC at room temperature. Benefiting from the broadband spectral coverage inherent of this technique, two distinct transient emission species associated with bacteriochlorophylls B and P are directly identified, with Stokes shifts determined to be ~197 and 450 cm−1, respectively. The ultrafast energy transfers from bacteriopheophytin H to B (98 fs) and from B to P (170 fs) are unveiled through fitting the emission dynamics. Notably, the anticipated sub-200 fs lifetime of B emission significantly extends to ~400 fs, suggesting a plausible coupling between the electronic excited state of Band the vibronic states of P, potentially influencing the acceleration of the energy transfer process. These findings should pave the way for understanding the impact of vibronic dynamics on the photo-induced primary processes in the photosynthetic reaction center.

Early Bacteriopheophytin Reduction in Charge Separation in Reaction Centers of Rhodobacter sphaeroides

A question at the forefront of biophysical sciences is, to what extent do quantum effects and protein conformational changes play a role in processes such as biological sensing and energy conversion? At the heart of photosynthetic energy transduction lie processes involving ultrafast energy and electron transfers among a small number of tetrapyrrole pigments embedded in the interior of a protein. In the purple bacterial reaction center (RC), a highly efficient ultrafast charge separation takes place between a pair of bacteriochlorophylls: an accessory bacteriochlorophyll (B) and bacteriopheophytin (H). In this work, we applied ultrafast spectroscopy in the visible and near-infrared spectral region to Rhodobacter sphaeroides RCs to accurately track the timing of the electron on BA and HA via the appearance of the BA and HA anion bands. We observed an unexpectedly early rise of the HA− band that challenges the accepted simple picture of stepwise electron transfer with 3 ps and 1 ps time constants. The implications for the mechanism of initial charge separation in bacterial RCs are discussed in terms of a possible adiabatic electron transfer step between BA and HA, and the effect of protein conformation on the electron transfer rate.