Abstract
The small-angle X-ray scattering technique (SAXS) is proposed for the investigation of equilibrium macromolecular interactions of the enzyme-substrate type in solution. Experimental procedures and methods of analysing the data obtained from SAXS have been elaborated. The algorithm for the data analysis allows one to determine the stoichiometric, equilibrium and structural parameters of the enzyme-substrate complexes obtained. The thermodynamic characteristics for the formation of complexes of tRNA Phe with phenylalanyl-tRNA synthetase have been determined and demonstrate negative cooperativity for binding of the two tRNA Phe molecules. The structural parameters ( R g, R c, semi-axes) have been determined for free phenylalanyl-tRNA synthetase and tRNA Phe from E. coli MRE-600 and of enzyme complexes possessing one and two tRNA Phe molecules, indicating structural rearrangements of the enzyme in the interaction with tRNA Phe.
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