Analysis of Metabolic Control:- The Response Coefficient Expresses the Effect of an Outside Controller on Flux through a Pathway
We can also derive a quantitative expression for the relative impact of an outside factor (such as a hormone or growth factor), which is neither a metabolite nor an enzyme in the pathway, on the flux through the pathway. The experiment would measure the flux through the pathway (glycolysis, in this case) at various levels of the parameter P (the insulin concentration, for example) to obtain the response coefficient, R, which expresses the change in pathway flux when P ([insulin]) changes.
The three coefficients C, ɛ, and R are related in a simple way: the responsiveness (R) of a pathway to an outside factor that affects a certain enzyme is a function of (1) how sensitive the pathway is to changes in the activity of that enzyme (the control coefficient, C) and (2) how sensitive that specific enzyme is to changes in the outside factor (the elasticity, ɛ): R=C. ɛ
Each enzyme in the pathway can be examined in this way, and the effects of any of several outside factors on flux through the pathway can be separately determined. Thus, in principle, we can predict how the flux of substrate through a series of enzymatic steps will change when there is a change in one or more controlling fac tors external to the pathway. Box 15–3 shows how these qualitative concepts are treated quantitatively.
