Trace element speciation at cell membranes: aqueous, solid and lipid phaseeffects

Biological interest in trace element speciation has tended to be polarised in very different ways according to the concerns of the investigators. Much of the ecological interest has centred on the effects of metal ions in the external environment with the ''free metal ion model" dominating discussio ns of potential toxicity. By way of contrast biochemists have been much mor e concerned with the stereochemical and kinetic aspects of specificity in m etal-protein interactions in the cytoplasm. Separating these two sets of in terests are the membrane biophysicists whose studies have concentrated on t he channel concept. All three groups have tended to ignore speciation onto the solid phase. In the overall biological context, trace element speciatio n in the cell is more concerned with kinetics and the evolution of specific ity of interaction between diverse ligands than with the conditions for equ ilibrium.