STEP 0
pyruvate dehydrogenase complex

The complex consists of 3 noncovalent enzymes.  The 3 are closely packed and substrate is passed quickly from one to the next.  Step 0 is not the only gateway to the TCA cycle; acetyl-CoA is also produced from the b-oxidation of fatty acids and can enter the cycle directly.
Pyruvate decarboxylase (PDC) catalyzes the decarboxylation of pyruvate and transfer of the acetyl group to lipoic acid.
Dihydrolipoamide acetyltransferase  regulates the nucleophilic attack by coenzyme A on the carbonyl carbon
of the acetyl group.
Lipoic acid leaves and is oxidized by dihydrolipoamide dehydrogenase.
substrate: pyruvate (CO2COCH3)
product: acetyl-CoA (CoAS-COCH3)
Citric Acid Cycle
  Heather Shepheard
  Tainted by Chemical X
pyruvate decarboxylase
dihydrolipoamide acetyltransferase
dihydrolipoamide dehydrogenase