STEP 3
Isocitrate Dehydrogenase

Oxidative decarboxylation of isocitrate to a-ketoglutarate occurs in 2 steps.

In the first step, isocitrate is oxidized to form the intermediate, oxalosuccinate. This step reduces NAD+ to NADH. 

Oxalosuccinate is a b-keto acid and easily decarboxylated.  This occurs in the second step, producing CO2 and a-ketoglutarate.
 
DG = -17.5  kJ/mol
DGº' = -8.4  kJ/mol
Keq =  29.7

substrate: isocitrate (CO2CH2CH(CO2)CH(OH)CO2)
product: a-ketoglutarate (CO2CH2CH2COCO2)
  Citric Acid Cycle
  Heather Shepheard
  Tainted by Chemical X
isocitrate dehydrogenase