Low temperature spectroscopy of proteins. Part II: Experiments with single protein complexes

In this part of the review we describe aspects of the physics of proteins at low temperature as they are reflected in the spectra of individual pigment-protein complexes. The focus of this review is on the spectral diffusion of chromophores that are naturally embedded in light-harvesting complexes from purple bacteria. From the spectral diffusion behaviour we can deduce details about the organisation of the energy landscape of the protein and discuss the implications for the motions of the protein in conformational phase space.