Preparation of metal ion buffers for biological experimentation: A methods approach with emphasis on iron and zinc

Transition metal ions are a challenge to study in physiology because of problems associated with solubility, oxidation, binding, and attaining appropriate free activities in solution. This review discusses these problems and potential ways of accommodating them. Special attention is given to iron and zinc ions, but many of the concepts can be applied for studying other transition metals. Selection of reagents appropriate for metal work (including water, salts, noncomplexing pH buffers) is briefly discussed. Calculation of the solubility product (K-sp) for common iron and zinc precipitates is covered, as well as techniques used to solubilize Fe3+ with organic chelates. Factors that affect Fe2+ oxidation are mentioned, and the use of ascorbate as a reducing agent is considered. Measurement of the rate of Fe2+ oxidation (or Fe3+ reduction) with the Fe2+ chromophores ferrozine and BPS is also discussed. Generation of a free metal ion activity through use of metal buffers (chelators) is discussed. Theoretical problems associated with this technique are explored, and selected shareware metal ion buffer calculators are described. Finally, techniques for measuring and minimizing nonspecific binding of iron and zinc ions to biological membranes are considered. J. Exp. Zool. 292:507-522, 2002. (C) 2002 Wiley-Liss, Inc.