Question

Isocitrate dehydrogenase catalyzes the oxidative decarboxylation of D-isocitrate to a-ketoglutarate according to the scheme (1):

D-Isocitrate + NAD+ → a-ketoglutarate + NADH + CO2 + H+ (1)

Use the following half reactions (2,3) and the corresponding reduction potentials to
determine the standard free energy for reaction (1).

a-ketoglutarate + 2e- + CO2 + H+ → D-Isocitrate (2) (Eo’ = -0.38 V)

NAD+ + 2e- +2H+ → NADH + H+ (3) (Eo’ = -0.32 V)

Answer: -11.6 kJ/mol Please explain steps

Answer 1

Reduction : NAD+ + 2e- +2H+ → NADH + H+           Eo = - 0.32 V

Oxidation : D-Isocitrate -----------> a-ketoglutarate + 2e- + CO2 + H+    ,    Eo = - 0.38 V

Eocell = Eored - Eo oxidation

          = - 0.32 - ( - 0.38)

Eocell = 0.06 V

delta Go = - n F Eocell

              = - 2 x 96485 x 0.06 x 10^-3

delta Go   = - 11.6 kJ/mol