In the citric acid cycle, malate is dehydrogenated to oxaloacetate in a highly endergonic reaction with a ΔG’o of +30 kJ mol-1: L‐malate + NAD+ ⇌ oxaloacetate + NADH + H+ Calculate the equilibrium constant K’eq of this reaction. What is the implication of this result?

Respuesta :

Answer :  The value of [tex]K_{eq}[/tex] of this reaction is, [tex]5.51\times 10^{-6}[/tex]

At equilibrium, [L-malate] > [oxaloacetate]

Explanation :

The relation between the equilibrium constant and standard Gibbs free energy is:

[tex]\Delta G^o=-RT\times \ln K_{eq}[/tex]

where,

[tex]\Delta G^o[/tex] = standard Gibbs free energy  = +30 kJ/mol = +30000 J/mol

R = gas constant = 8.314 J/K.mol

T = temperature = [tex]25^oC=273+25=298K[/tex]

[tex]K_{eq}[/tex]  = equilibrium constant  = ?

The given reaction is:

[tex]\text{L-malate}+NAD^+\rightleftharpoons \text{oxaloacetate}+NADH+H^+[/tex]

[tex]\Delta G^o=-RT\times \ln K_{eq}[/tex]

[tex]+30000J/mol=-(8.314J/K.mol)\times (298K)\times \ln K_{eq}[/tex]

[tex]K_{eq}=5.51\times 10^{-6}[/tex]

Therefore, the value of [tex]K_{eq}[/tex] of this reaction is, [tex]5.51\times 10^{-6}[/tex]

As, the value of [tex]K_{eq}[/tex] < 1 that means the reaction mixture contains reactants.

At equilibrium, [L-malate] > [oxaloacetate]