Biological Systems Ion Exchange

R. J. P. Williams, Imperial College, London, UK

Copyright © 2000 Academic Press

There are two very different processes which are described under the heading of ion exchange within biological systems. The first is exchange in an aqueous environment of two different ions, MA and MB, held by a molecule in free solution, or in a precipitate, or on a membrane surface:

Here, M is a metal cation and X is an anion, often an organic molecule which can be as large as a protein or DNA. Exchange of anions is also possible, as in the equilibrium:

Both eqns [1] and [2] have been written for exchanging ions of equal charge type n. This is not a necessary condition, so we can also consider:

Again, the charge balance shown so far in the equations is not essential, so we must also examine the situation of electrogenic exchange:

where charge distribution is associated with MX changes. Before considering the second way in which ion exchange can occur across a membrane, we give one or two examples of ion exchange to and from a bound condition in a single aqueous solution.

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