7Li Nuclear‐Magnetic‐Resonance Study of Lithium Binding to Myo‐Inositol Monophosphatase

The interaction of Li' with myn-inositol monophosphatase was studied by 7Li-NMR spectroscopy. Li' binding to the enzyme induces a downfield shift and broadening of the 7Li-NMR signal. Changes of the chemical shift were used to follow the titration of the enzyme with lithium and to determine a dissociation constant, Kd = (1 .0 2 0.1) mM. Only one major binding site/enzyme subunit was inferred. The complex forms independently of the presence of inorganic phosphate. Metals from the group IIa of the periodic table compete with Li' binding with the affinity increasing in the order Mg" < Ca" < Be". In contrast to lithium, their binding is enhanced by phosphate.