Temporal Analysis of the Transition between Steady States

Abstract

Most Studies of metabolic control have concentrated on defining pathway flux and its determinants. In particular the fine-control of enzyme activity and the homeostatic maintenance of steady states has been a focus of attention. In the cell many changes are more dramatic and involve large changes of flux. Much less attention has been given to the equally important topic of the time-scale on which such changes, and metabolic processes generally, operate. A full description of regulation of a system must include such temporal analysis. It is insufficient to ask of a pathway, cell or organism “How fast does it go?”, it is also necessary to ask “How long does it take to get there?”. This temporal responsiveness sets the time-scale on which metabolism operates and is best described by the pathway transition or transient time, τ. The reluctance to study pathway dynamics probably arises partly from a mistaken belief that real-time measurements or a detailed knowledge of pathway kinetics is necessary. Either way the experimentation would be difficult.