MOSSBAUER STUDY OF SPIN-LATTICE RELAXATION AND INTRAMOLECULAR MOTIONS IN TRANSFERRIN

A new approach for the investigation of intramolecular motions in proteins, based on the study of spin-lattice relaxation of ferric iron in the protein active centres, has been developed. The Mossbauer spectra of dry and hydrated transferrin enriched with Fe-57 isotope have been obtained. They revealed a paramagnetic hyperfine structure with the magnetic splitting of lines up to room temperature. This allowed one to investigate experimentally high temperature conformational motions in the protein and to study their influence on spin-lattice relaxation. A theoretical model for the fitting of the relaxation spectra has been developed that made it possible to restore the frequency distribution of spin-lattice relaxation rates from experimental data. Two peaks in these distributions at 10(8) s(-1) and 10(10) s(-1) have been discovered in the temperature interval 78-300 K. It proves that there is a difference in the dynamic states of two iron atoms in the active centres of the transferrin molecule for N- and C-lobes. The approach developed for the study of intramolecular dynamics of proteins based on the analysis of spin-lattice relaxation increases the frequency range of the molecular motions under investigation at least one order in comparison with the traditional methods, based on the study of the Mossbauer effect probabilities and mean-square displacements of atoms.