Adenylate charge

Thus ATP is the effective controller of metabolism but because AMP + ADP + ATP is constant, it is really the ratio of adenine nucleotides which is important This ratio is termed die adenylate charge or energy charge and is expressed as ... 

The energy status of a cell can be calculated from the levels of adenylate nucleotides and is expressed as the energy or adenylate charge ... 

Fig. 2.34. Periodic variation of the adenylate charge in the course of sustained oscillations in the allosteric model with positive feedback. At the unstable steady state, the charge is equal to 0.945 (Goldbeter, 1974).

Taking this one step further, perhaps even an inorganic gene may have been provided by clay mineral sources. Earliest clay samples are of a mineral called montmorillonite that consists of sheets of aluminosilicates in which Fe2+, Fe3+ and Mg2+ are substituted for some of the Al3+, and Al3+ is substituted for Si4+. The oxygen content of the layers does not change and the alternative valencies allow the production of positive and negatively charged layers. Dramatically, Paecht-Horowitz and co-workers showed that the amino acid adenylate could be polymerised with up to 50 units on the montmorillonite surface in aqueous solution. Similar condensation reactions for carbohydrates on hydrotalcite surfaces have... 

Significant decline in adenylate energy charge in gills after 10 days exposure normal by day 30 of exposure LC50 (96 h)... 

Aminoacyl adenylates (296), which are formed from protein amino acids and ATP, act as acylating agents towards t-RNAs, acylating their terminal 3 -hydroxy groups. These charged tRNAs are then used in protein synthesis. Little is known about the reactivity of aminoacyl adenylates (296), and studies are now reported of a model compound, alanyl ethyl phosphate (297). As expected, hydrolysis in both acid and base involves attack at the C=0 group of (297) with departure of ethyl phosphate. Metal ions (Cu +, Zn +) were found to act as catalysts of the hydrolysis. 

The energy charge (or adenylate energy charge) is estimated by substituting the measured ATP, ADP, and AMP concentrations into the following expression ... 

The energy charge quotient has a value of unity (or, 1.00) when only ATP is present and a value of zero when only AMP is present. Thus, the adenine nucleotide system is said to be fully charged at EC = 1 and fully discharged at EC = 0. At intermediate values, the adenine nucleotides are interconverted by adenylate kinase, and their concentrations are constrained by the adenylate kinase mass action ratio ... 

When IRS, [14C]Ile, tRNA, and ATP are mixed in the quenched-flow apparatus (Figure 7.6), the initial rate of charging of tRNA extrapolates back through the origin without any indication of a burst of charging. The burst of pyrophosphate release is due to the formation of the aminoacyl adenylate before the transfer of the amino acid to tRNA. 

Relative concentrations of ATP, ADP, and AMP as a function of the adenylate energy charge. The adenylate kinase reaction was assumed to be at equilibrium, and a value of 1.2 was used for its effective equilibrium constant in the direction shown in the equation in the text. 

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