The linear Onsager coefficients for biochemical kinetic diagrams as equilibrium one-way cycle fluxes

Abstract

In a biochemical kinetic diagram¹, the various discrete states of an enzyme or enzyme complex are represented by points, and interstate transitions are represented by lines. Figure 1 is an example. I show here that, for steady states near equilibrium, the phenomenological Onsager coefficients in the linear flux–force equations that are a consequence of any such diagram have a transparent physical interpretation: these coefficients are simple combinations of one-way cycle fluxes¹ at equilibrium. The existence of this kind of relationship was pointed out recently in an appendix of a paper² on another subject. I present here the explicit connection between the phenomenological coefficients and the one-way cycle fluxes of the diagram. These coefficients are considered by many scientists to be strictly empirical and incomprehensible. My report provides a simple interpretation of them, at the molecular level, for any biochemical kinetic diagram. This is analogous to the molecular interpretation of phenomenological equilibrium thermodynamics that is provided by statistical mechanics.