MAGNESIUM VS MANGANESE COFACTORS FOR METALLONUCLEASE ENZYMES - A CRITICAL-EVALUATION OF THERMODYNAMIC BINDING PARAMETERS AND STOICHIOMETRY

An experimental analysis of Mg2+ vs, Mn2+ binding to Escherichia coli ribonuclease H and exonuclease III enzymes by isothermal titration cal orimetry clearly demonstrates a 1:1 stoichiometry for metal binding to ribonuclease H, hut distinct metal-dependent behaviour for exonucleas e III, suggesting caution in the interpretation and generalization of results concerning the location and stoichiometry of Mg2+ binding site s from crystallographic and mechanistic experiments with Mn2+.