Intrinsic Phosphorescence of Proteins

Abstract

Various methods of luminescence analysis are currently used on a large scale for studies of different aspects of the dynamics of protein structure as well as of conformational analysis of protein macromolecules. In recent years, many specialists have been displaying a keen interest for phosphorescence which is a spin-forbidden emissive transition of a molecule from the excited triplet state to the ground singlet one. The lifetime of phosphorescent molecules ranges from a few tens of seconds to 10 ⁻⁵ s, which makes it possible to study processes occurring with their participation within this time interval. Owing to the long lifetime of the triplet, the phosphorescence method allows, in principle, to significantly expand the time interval of the processes under study (at the molecular level), as compared to the fluorescence method. Until recently, however, application of this method in spectroscopy of proteins had been very limited. This can be explained by the fact that the parameters of low temperature phosphorescence depend relatively little on the structural organization of proteins. This is due to unification of the properties of the macro- environment of natural chromophores of proteins resulting from the freezing of samples to the temperature of liquid nitrogen. Phosphorescence of proteins at room temperature was observed for the first time during studies of solid protein structures — keratin of wool and fibroin of silk as well as protein crystals and films (Konev and Bobrovich 1966; Konev 1967).