How do external parameters control fluxes and concentrations of metabolites? An additional relationship in the theory of metabolic control.

The flux through a metabolic pathway can be controlled by external signals from the environment. These signals are formally described as changes in external parameters, such as concentrations of external metabolites (substrates or effectors) or physical parameters, e.g. temperature, pH, ionic strength. It was proved that the response coefficient of the flux (or of the concentration) to a change in an external parameter is the weighted average of external elasticities of pathway enzymes towards this parameter; weight factors are the control coefficients of corresponding enzymes. As compared with the previously known relationships these ones are applicable to the more common case of parameters acting on more than one enzyme. Along with other applications, the use of the obtained relationships for control analysis of moiety-conserved cycles is considered.