Adenine Nucleotides as Regulators

The three adenine nucleotides, ATP, ADP, and AMP form a very important group of regulators which operate on a large number of reactions to adjust the rate of formation of ATP to its rate of utilization. One well-known example is the effects of ATP and AMP on 6-phosphofructo-kinase activity. ATP inhibits the enzyme and AMP decreases this inhibition (i.e., has a deinhibitory effect). The combined effects of ATP and AMP on the enzyme can be considered to produce a feedback link between ATP utilization and its formation via glycolysis  

In many tissues, the three nucleotides are maintained in equilibrium by the enzyme adenylate kinase which catalyses the reaction. 

The effects of adenine nucleotides on metabolic regulatory systems are so widespread that Atkinson has introduced the concept of energy charge (E) which is defined as 

Since the control of enzyme activity can be analyzed quantitatively by using power approximations, it is possible to apply this to the control of an activity by the adenine nucleotides. Let us assume that an activity ( ) is influenced by the concentrations of the three nucleotides, then 

To do this it is necessary to express the concentration of ADP and AMP in terms of that of ATP (cf. Section in,D) and the required functions are obtained from the following equations [see Eq. (16)]. As a result of the adenylate kinase equilibrium, 

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