BOVINE INOSITOL MONOPHOSPHATASE - STUDIES ON THE BINDING INTERACTIONSWITH MAGNESIUM, LITHIUM AND PHOSPHATE IONS

Rapid equilibrium dialysis has been used to show that recombinant bovi ne brain inositol monophosphatase binds one equivalent of P(i) per sub unit of enzyme. P(i) is only bound in the presence of Mg2+ ions. The d issociation constant for the equilibrium is approximately 50 muM. This value of K(d) is independent of the concentration of the Mg2+ ions an d of the presence or absence of Li+ ions. Lithium ions which inhibit t he enzyme uncompetitively are not able to support the binding of the P (i) to the enzyme. The observation that P(i) only binds in the presenc e of Mg2+ ions supports similar conclusions made in experiments which studied the protection of the enzyme from proteolytic degradation and chemical modification.