Electron nuclear double resonance characteristics

NMR and EPR techniques provide unique information on the microscopic properties of solids, such as symmetry of atomic sites, covalent character of bonds, strength of exchange interactions, and rates of atomic and molecular motion. The recent developments of nuclear double resonance, the Overhauser effect, and ENDOR will allow further elucidation of these properties. Since the catalytic characteristics of solids are presumably related to the detailed electronic and geometric structure of solids, a correlation between the results of magnetic resonance studies and cata lytic properties can occur. The limitation of NMR lies in the fact that only certain nuclei are suitable for study in polycrystalline or amorphous solids while EPR is limited in that only paramagnetic species may be observed. These limitations, however, are counter-balanced by the wealth of information that can be obtained when the techniques are applicable. 

The structures now available at 5-8 A resolution allow differentiation of protein a-helices from double-helical regions of rRNA based on their structural characteristics some protein -sheets can also be seen. The structures of several individual ribosomal proteins have been solved by X-ray crystallography or nuclear magnetic resonance spectroscopy, and the X-ray data on the whole 508 particle have been correlated with the previously determined structures of individual proteins. As expected, the accumulated data fromlEM, cross-linking, and neutron diffraction helped to position these protein stmctures within the ribosome electron density and will continue to direct placement of proteins and specihc regions of rRNA. 

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