The symbiosis of metal ion and protein chemistry
The binding of metal ions to biological macromolecules is made extremely complicated by the existence of different compartments in cells, organs and whole organisms. The compartments are not at equilibrium. Apart from considerations of binding constants and rates of combination of metal and ligand with which an inorganic chemist is familiar the distribu— tion of elements within biological systems is controlled by a mon—equili-brium partitioning between the compartments. The compartments can differ simply in the sense that they are at different pH or redox values. More complicated situations arise through other energised activities within and between compartments. Particularly important are (i) the controlled syn— theses of different proteins and ligands in a given compartment (ii) the pumping of specific ions in and out of compartments (iii) the energised movement of proteins and metalloproteins across membranes. The pecularities of the function of one metal ion are related to this control over its distribution. Catalytic function of an element can only be understood in the light of this sophisticated fractionation of the elements in space.