6] Metal-buffered systems

Abstract

The design of a metal ion buffer system useful in a given enzymological application is subject to a number of different requirements. 1. The total concentration of added metal ion, Mt, should be large enough to damp out the effect of any adventitious quantities of the same metal ion and to overwhelm adventitious quantities of other metal ions. 2. The ratio of free to bound ligand should be high enough that the calculated ratio between the concentrations of free metal ion M and Mt will not be unduly sensitive to uncertainties in the values of metal-ligand stability constants. If possible, [Lt]/[Mt] should be large enough that the variation of free metal ion concentration, [M], with [Mt] will be effectively linear in the range of interest. 3. The concentrations of metal ion buffer species, both the free ligand and metal-ligand complexes, should be kept reasonably low in order to minimize the possibility of perturbation of the enzyme/metal ion equilibrium. The best design will be that which most successfully balances these sometimes opposing requirements.