113Cd-1H heteroTOCSY: a method for determining metal-protein connectivities

113Cd-1H NMR correlation experiments have been extremely useful for determining the amino acid ligands that form metal-binding sites in proteins. To date, the majority of these methods have used heteronuclear multiple-quantum transfer as the basis for establishing correlations. In this paper, we demonstrate the feasibility of using correlation methods that employ heteronuclear cross-polarization (heteroTOCSY) as viable alternatives. Additionally, we couple heteroTOCSY with selective excitation and transfer procedures to take advantage of the small number of heteronuclei usually present in metalloprotein systems. One- and two-dimensional experiments are presented as examples of these techniques.