EXPLORING THE STRUCTURE OF THE REACTION CENTER FROM THE AEROBIC PHOTOSYNTHETIC BACTERIUM ROSEOBACTER DENITRIFICANS WITH FOURIER TRANSFORM INFRARED SPECTROSCOPY

摘要

About 20 years ago aerobic, bacteriochlorophyll a containing photosynthetic bacteria were discovered (Harashima et al 1978). In contrast to the traditional purple bacteria as e.g., Rhodobacter (Rba ) sphaeroides and Blastochloris viridis these type ofbacteria require oxygen to build up a photosynthetic apparatus and to perform light-induced charge separation in the reaction center (RC). The need of oxygen was explained by a relatively high midpoint potential and the prereduction of the primary electron acceptor, QA, in the RC before illumination under anoxic conditions. More recently, we derived a structural model of the RC from the aerobic photosynthetic bacterium Roseobacter (Rsb.) denitrificans by homology modelling (Herter et al 1998, Hucke 2002). FTIR difference spectroscopy has been established as a method of choice to probe interactions between the primary electron donor, D, Q_A and the secondary electron acceptor, Q_B, and the surrounding protein matrix during light-induced electron transfer. In this work we focus on the quinone binding pockets. The resulting light-induced FTIR difference spectra were interpreted based on both the structural model and the bands assignments to specific vibrational modes in the corresponding FTIR difference spectra from Rba. sphaeroides.