Near-equilibrium reactions

Figure 3.27 Representation of the rates ofthefonvard and reverse reactions for non- and near-equilibrium reactions in one reaction in a hypothetical pathway. The values represent actual rates, not rate constants. The net flux through the pathway is given by (1/f-l/r). In the non-equilibrium reaction, the rate of the forward reaction dominates, so that the net flux is almost identical to this rate. In the near-equilibrium reaction, both forward and reverse rates are almost identical but considerably in excess of the flux.

Figure 8.11 Five near-equilibrium reactions involved in transamination of five different amino adds. Three enzymes are involved in these reactions (1) alanine aminotransferase (2) aspartate aminotransferase (3) branched-chain amino acid aminotransferase, i.e. one enzyme catalyses the three reactions. (The branched-chain amino acids are essential.)...

Near equilibrium, reaction rates become approximately linear in their deviation from equilibrium conditions. Suppose fe, is a point on the equilibrium curve of... 

This reaction is readily reversible (a near-equilibrium reaction) and has a AG of —0.7 kcal/mol (—2.9 kJ/mol). It proceeds with the formation of intermediates of the enzyme with succinyl phosphate and with phosphate (Pi), the latter being linked to histidyl residue of the enzyme (E) ... 

Fructose-6-phosphate is then converted to glucose-6-phosphate by reversal of another near-equilibrium reaction of glycolysis. In the last reaction in gluconeoge-... 

In general, flux through the glycolytic pathway is regulated by the activity of hexokinase, 6-phosphofructo-l-kinase, and pyruvate kinase. These enzymes have in common that the metabolic steps they catalyze are non-equilibrium reactions. All other enzymes in the glycolytic pathway appear to catalyze a near-equilibrium reaction and are, therefore, not subject to regulation of the conversion of glucose to pyruvate or lactate. 

These limitations of 5(1 A), parallel those noted in Section III for IT(5 x). Namely, just as S(Fp A) drives only nearly reversible processes, lF(5 x) drives only near equilibrium reactions —> Xp. 

In a near-equilibrium reaction the reverse process (u,) is not insignificant and hence must be taken into account. For the reaction... 

The effect of a near-equilibrium reaction in a substrate cycle can be included when calculating the sensitivity of each route by the product rule. Thus, if Rp denotes the reversibility of F,... 

The important difference between the two types of reaction is that, with a near-equilibrium reaction, changes in the concentration of product can change the rate of the reverse reaction and hence can influence the flux through the reaction by a mass action effect. 

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