Relationship of thermal quenching of protein fluorescence to intramolecular structural mobility

Temperature dependence (over the range from 5 to 75 degrees C) of the fluorescence quantum yield--the parameter sensitive to the rapid (ns) mobility--has been investigated. For native proteins containing 1--2 fluorescing chromophores this dependence in the non-denaturing temperature range can be described by the equation 1/q = a + b . T/eta (a and b are temperature-independent constants, T is the temperature (K), eta is the viscosity of water, (cP). The linearity of the plot of 1/q vs. T/eta probably indicates that the internal mobility of different parts of the protein globule is limited by the diffusion of the molecules of the solvent. The peculiarity of individual protein structures is reflected by various absolute values of the constants of quenching rates. The results of the studies indicate that an analysis of the temperature dependence of the protein fluorescence quantum yield (thermal quenching curves) might be a new experimental approach to the study of the mobility of protein structures. The thermal quenching curves of proteins could be used as a measure of the temperature dependence of the rapid reverse structural mobility.