An instrumental technique used to determine the three-dimensional (3-D) structure of biological molecules. NMR spectroscopy and x-ray crystallography (q.v.) are the only methods capable of analyzing the structures of proteins and nucleic acids at atomic resolution. NMR spectroscopy exploits the behavior of certain atoms when they are placed in a strong static magnetic field and exposed to short pulses of energy in the radio-wave frequency range. For biological samples, the important atoms are H-1, N-15, and C-13, and the magnets used are 10,000–15,000 times stronger than the earth's magnetic field. To increase the level of N-15 and C-13 in the molecular targets, microorganisms from which the molecules are extracted are grown on media enriched with these isotopes. When placed in a strong magnetic field, the atomic nuclei of these atoms exhibit a property called nuclear spin, whereby they behave like tiny compass needles and orient themselves with respect to the magnetic field. When exposed to pulses of radio waves of specific frequencies, the oriented nuclei jump to higher-energy states in which the spin is opposed to the magnetic field. The nuclei are now said to be in resonance, and they emit radio frequency radiation when they revert to their lower-energy states. The amount of energy needed to achieve resonance is dependent on the properties of each nucleus and its chemical environment, and plots of the strengths of the resonance signals versus radio-wave frequencies provide information about the nature of atoms and their proximity to one another. NMR data are coupled with computational tools to produce 3-D structures of biomolecules, which are stored in easily accessible databases. The first protein structure determined by NMR spectroscopy was that of a bull seminal proteinase inhibitor. NMR spectroscopy techniques can also be extended to such areas as the study of molecular interactions, molecular motion, and the rate of chemical reactions. See Chronology, 1985, Williamson et al.; 1966, Ernst and Anderson; 1991, Ernst; 2002, Wüthrich et al.; Antennapedia, proteomics.
Subjects: Genetics and Genomics.