[Luminescent analysis of the structure of human alpha-1-microglobulin]

The spectra of absorption, fluorescence, and excitation of fluorescence of preparations of alpha-1-microglobulin isolated from human urea by two methods, gel chromatography and immunoaffinity chromatography with additional purification by activated charcoal, have been investigated in ultraviolet and visible regions. A possible nature of low-molecular compounds coloring alpha-1-microglobulin yellow-brown and their role in stabilizing the structure of protein globule are discussed. The action of urea (1.0-10 M) and guanidine hydrochloride (0.25-6 M) on the conformational state and the fast (nanosecond) internal dynamics of alpha-1-microglobulin has been investigated by the method of tryptophan fluorescence. It has been shown that the unfolding of alpha-1-microglobulin under the action of these denaturants is associated with a significant increase in the nanosecond internal dynamics of protein. The ability of alpha-1-microglobulin to restore the initial conformation characteristic for the native protein and the internal dynamics after the unfolding of the globule by 10 M urea and 6 M guanidine hydrochloride has been ascertained. It has been found that alpha-1-microglobulin isolated by the method of gel chromatography can exist in solution of 4-6 M urea in a thermodynamically stabile partialy folded state.