Supply-demand analysis a framework for exploring the regulatory design of metabolism

The living cell can be thought of as a collection of linked chemical factories, a molecular economy in which the principles of supply and demand obtain. Supply-demand analysis is a framework for exploring and gaining an understanding of metabolic regulation, both theoretically and experimentally, where regulatory performance is measured in terms of flux control and homeostatic maintenance of metabolite concentrations. It is based on a metabolic control analysis of a supply-demand system in steady state in which the degree of flux and concentration control by the supply and demand blocks is related to their local properties, which are quantified as the elasticities of supply and demand. These elasticities can be visualized as the slopes of the log-log rate characteristics of supply and demand. Rate characteristics not only provide insight about system behavior around the steady state but can also be expanded to provide a view of the behavior of the system over a wide range of concentrations of the metabolic intermediate that links the supply and the demand. The theoretical and experimental results of supply-demand analysis paint a picture of the regulatory design of metabolic systems that differs radically from what can be called the classical view of metabolic regulation, which generally explains the role of regulatory mechanisms only in terms of the supply, completely ignoring the demand. Supply-demand analysis has recently been generalized into a computational tool that can be used to study the regulatory behavior of kinetic models of metabolic systems up to genome-scale.