Steady-state properties of coupled systems in mitochondrial oxidative phosphorylation.

At steady state there is effective coupling among various otherwise independent membrane and internal mitochondrial systems that share the same substrates or ligands (e.g., H+, Ca2+, Pi, ADP, ATP). The number of different systems, coupled through shared substrates or ligands, is no doubt very large. But, just as an infinite series can be approximated by a finite number of terms, here the number of systems included in the analysis can be limited, as an approximation. In two previous papers, the basic but oversimplified set of four tightly coupled systems was studied. These are: respiratory chain; reverse ATPase; proton-phosphate cotransport; and ADP-ATP exchange. Essentially as illustrations of the methodology required for a more realistic analysis, two much more complicated examples are formulated here: eight tightly coupled systems, and the original four systems but with the tight coupling relaxed in two of these four.