Pressure-induced structural reorganizations due to the presence of an internal cavity in the photochemical reaction centre (RC) from Rhodobacter sphaeroides

Abstract

Spectroscopic measurements at high pressures have been used to investigate the nature of the couplings that govern the structure, spectral properties and function of the reaction centers (RC) from Rhodobacter sphaeroides. Up to at least 0.6 GPa, the RC proteins from the wild-type (WT) and R26.1 strains do not loose their three dimensional structures at room temperature. However, the RC from strain R26.1, which has a large internal cavity due to the absence of the carotenoid chromophore, experiences nearly an order of magnitude decrease in oscillator strength of the Qy electronic transition state of the primary electron donor (P) between 0.3 and 0.6 GPa. Also, Raman spectra indicate that a number of local reorganizations in the binding site of P occur up to about 0.3 GPa. However, no major structural reorganizations of P occur at higher pressures. Thus, the pressure-induced change in the absorption of P in R26.1 presumably is caused by an increase in the mixing between its singlet excited and optically forbidden charge-transfer states. Thus, the pressure-induced change in the absorption of P in R26.1 presumably is caused by an increase in the mixing between its singlet excited and optically forbidden charge-transfer states.