| Abstract
| - We have employed the technique of single-molecule fluorescence microspectroscopy toinvestigate the spontaneous conformational evolution of individual peripheral LH2 complexes from thepurple bacterium Rhodopseudomonas acidophila. Fluorescence microscopy is a sensitive tool, which allowsthe spectral changes of single complexes to be monitored on a time scale from 0.1 s to many minutes.Here we have investigated “natural” (occurring in the absence of excitation) spectral diffusion after aspectral jump has occurred. In a quarter of all the observed spectral jumps recorded with the LH2 complexes,a further spontaneous evolution occurs, in the absence of illumination, that results in the formation of adifferent spectroscopic state. We suggest that this is due to a natural conformational development of thepigment−protein complex, which so far has not been observed for this type of complex at the single-molecule level. The functional significance of such structural rearrangements is not yet clear but may beassociated with the necessity for the light-harvesting complexes to adjust their shape in the densely packedphotosynthetic membrane.
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