Abstract

Bromine-81 magnetic resonance is used to detect the formation of ternary metal-protein-ligand complexes. Mercury is the metal; EDTA and lysine are the ligands; and acid phosphatase, α-chymotrypsinogen, and peroxidase are the proteins which are studied. The halide-ion probe method permits the determinations of the local correlation time and the bromide-ion exchange rate at the metal binding site. The local correlation time becomes longer as additional mass in the form of the ligand is added to the protein segment containing the metal binding site. The bromide-ion exchange rate increases upon formation of the ternary complex, which is consistent with the pattern of hetero-substitution in bromomercury (II) species. The major factors controlling the bromide-ion exchange rate appear to be steric.