Chemical potential of bound ligand, an important parameter for free energy transduction.

The chemical potential (mu(L,b)) of a ligand L bound to a protein or enzyme can be rigorously defined, and this paper describes some of its properties in relation to other thermodynamic parameters, with emphasis on thermodynamic parameters that may be used in the elucidation of the mechanism of biological free energy transduction. Free energy transduction involves the transfer of free energy from one molecule to another, and the actual transfer may often occur while both molecules are bound to the transducer enzyme, which means that mu(L,b) for one bound ligand increases at the expense of mu(L,b) for the other. The free energy change for the overall reaction may be very small, and it is not possible to express the phenomenon of transfer, in thermodynamic terms, without the explicit use of mu(L,b) as a parameter.