Resonance Raman studies of photosynthetic membrane proteins

Abstract

Examples of recent resonance Raman (RR) studies conducted at Saclay on reaction center (RC) proteins of photosynthetic bacteria and plants are given. These include structural studies of the primary donors of bacterial and Photosystem 1 RCs as well as of the early electron acceptors of bacterial and Photosystem 2 RCs. Pump-probe steady state difference RR experiments and time-resolved RR studies of the 12 ns-lived P+HQ state conducted on RCs of the R26 mutant of Rhb sphaeroides showed that a long-lived triggered protein conformational change occurs on a nanosecond timescale around the functional L-side bacteriochiorophyll a (BCh1) molecule in bacterial RCs upon formation of the )+jilcation state. The origin of the influence of the M210 tyrosine side-chain on the primary charge separation has been investigated on two sitedirected mutants. The mutations did not significantly alter the local interactions of any of the L-side pigments hence indicating that Tyr M208 must act directly on intermediate states of the charge separation. Fourier-Transform Raman spectroscopy has been successfully applied to BCh1 a and BPheo a in various environments. Strong preresonances occur with the Qy transitions. In particular in both the P and states the primary donor contributions appear to dominate the FTRR spectra of bacterial RCs. 1 .