Metal Ion NMR: Application to Biological Systems

Abstract

This chapter discusses the biological importance of metal ion nuclear magnetic resonance (NMR). Inorganic elements have a multitude of functions in biological systems, such as carriers of ionic signals, triggering of proteins, formation of structures, electron transport, and enzyme catalysis. All essential elements in biological systems and all elements of the periodic table have at least one potentially valuable isotope for NMR studies. This is because the NMR sensitivity of many biologically interesting nuclei is very low. NMR parameters are generally dependent upon the chemical nature of the nuclear environment and on its structure and dynamics. Thus, NMR spectroscopy may be used to identify and characterize metal ion binding sites on biological macromolecules and how these change during the course of biochemical reactions. The possibility of using NMR to determine metal ion populations of individual binding sites on a multisite protein is not matched by many other physical techniques. Metal ion NMR also makes it possible to address such elusive questions as cooperatively or anticooperativity of ion binding. As the relaxation of quadrupolar nuclei usually is caused by fluctuating electrical field gradients at the site of the nucleus, NMR studies can provide insight into ion binding to poly electrolytes, discriminate between nonspecific and specific ion binding, and are in general useful for testing theoretical models of ion binding