Formation of the covalent bond between thiamine and pyruvateThe proton on the carbon between the "N" and "S" of thiamine has a very low pK for a C-H bond and it dissociates easily. The resulting carbonion (negatively charged carbon atom) can attack a carbnyl (ketone) to generate a covalent bond

The bond between pyruvate and thiame has formed. This places a N+ in the right place t initiate an aldol reaction.

  1. A pair of electrons from the C+N double bond moves to the N+
  2. the electron cascade moves from the carboxyl group to here

The transition state is shown as well as CO2 has formed

  1. The transition state collapses back toward the original but instead of grabbing the CO2 it grabs a proton

the products are shown

  1. CO2 is shown
  2. acetaldehyde is formed but is still bonded to the thiamine
  3. the thiamine is released as the -O- moves to reform the C=O double bond
  4. the bond to thiamine goes back to form the carbanion

The enzyme is in is original state - except to reprotonate the acid to begin the next cycle

Pyruvate Decarboxylase Information

Enzyme Name

Pyruvate Decarboxylase

Reaction Catalyzed

Cleavage of C-C bond adjacent to a ketone to make carbon dioxide

Reaction Type

Aldol Reaction (thiamine dependent)

Pathway Involvement

Yeast only (in combination with ethanol dehydrogenase) Termination of glycolysis under anaerobic conditions


Thiamine pyrophophate is a required cofactor