The properties of intrinsic tryptophan fluorescence of two forms (molecular weight 2X 59 000 and 2X39 000) of tyrosyl-tRNA synthetase from bovine liver have been studied. The contributions of exposed and internal tryptophan residues into fluorescence spectrum of tyrosyl-tRNA synthetase have been determined in terms of the model of discrete structure-physical classes of tryptophanyls in the proteins. The temperature dependence of parameters of tryptophan fluorescence testified that temperature-induced mobility of separate protein fragments increased in temperature range from 40 °C to 75 °C. Analysis of temperature quenching of enzyme fluorescence in co-ordinate of the 1/q(T) and 1/q(T/η) indicated that the mobility of synthetase in the solution was regulated by diffusion characteristics of the solvent. It is true both for surface and for internal parts of protein.