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

Abstract
The interaction of Li+ with myo‐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 ± 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 Mg2+ < Ca2+ Be2+. In contrast to lithium, their binding is enhanced by phosphate.