While the TPP-stabilized carbanion intermediate in the pyruvate decarboxylase reaction went on to become protonated, however, the carbanion in the pyruvate dehydrogenase reaction acts as a nucleophile...While the TPP-stabilized carbanion intermediate in the pyruvate decarboxylase reaction went on to become protonated, however, the carbanion in the pyruvate dehydrogenase reaction acts as a nucleophile, attacking one of the sulfurs in a disulfide bridge of a coenzyme called lipoamide. (step 3 below).
