Coupling agents adenylate system

The coupling of reaction sequences through the adenylate system is entirely different from the two types of stoichiometric relationships discussed above. The stoichiometry of each reaction in which ATP is regenerated or used is, of course, fixed by the nature of the reaction, but the number and types of reactions in which ATP is involved have been determined by evolutionary processes, rather than by simple chemical necessity. Indeed the use of ATP as a coupling agent and the evolutionary adjustments of stoichiometric relationships for maximal metabolic advantage are at the very center of biological function. This fact is underscored by the participation of ATP in every extended metabolic sequence. 

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