The T 1 -accordion COSY experiment has been applied to acyl carrier protein (ACP) to locate the divalent ion binding sites in the protein using the paramagnetic ion, Mn 2 + , as a substitute for Ca 2 + . Replacement with Mn 2 + leads to an enhancement of proton spin-lattice (T 1 ) relaxation rates. These enhancements have a l/r 6 , distance dependence that makes them extremely useful in structural analyses. Ion-proton distances ranging from 3.0 to 9.0 Å have been obtained from this experiment and subsequently used as constraints in the molecular mechanics module of AMBER to refine a protein structure.