The mobility of chromatophore membranes from Ectothiorhodospira Shaposhnikovii revealed by Rayleigh scattering of Mössbauer radiation (RSMR) experiments

Abstract

Chromatophores from Ectothiorhodospira Shaposhnikovii in solvents of different viscosity were investigated by RSMR experiments in the temperature range between 112 K and room temperature. Additional RSMR-experiments were done on solvents only. The mobility of the molecules and within the molecules is the given by the Debye-Waller factor which yields the meansquare displacement, $\overline {\left\langle {x^2 } \right\rangle }$, averaged over the atoms in the system. The mobility of the atoms of the chromatophores roughly follows the mobility of the atoms of the solvents. At low temperatures the mobility of the chromatophores remains slightly larger than the mobility of the frozen solvent. At room temperature, however, $\overline {\left\langle {x^2 } \right\rangle }$ of the chromatophores remains significantly smaller.

Chromatophores in a glycerol-water mixture (0.001 M Tris-HCl buffer) and in water (0.05 M Tris-HCl buffer) show a different dynamic behaviour. A region with enhanced mobility near T=180 K was indicated for the chromatophores in the glycerolwater mixture.

A correlation has been suggested between the rate of electron transfer from the primary to the secondary quinone and the increase of the conformational mobility of the chromatophores in glycerol-water mixture.