Thiamin plays an essential role in the metabolism of carbohydrates as the diphosphate ester thiamin pyrophosphate, which is also called cocarboxylase.
Thiamin pyrophosphate is required for the oxidative decarboxylation of alpha-ketoacids by serving as an essential cofactor in multi-enzyme alpha-ketoacid dehydrogenase complexes. Identified thiamin pyrophosphate-dependent alpha-ketoacid dehydrogenases are pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase and branched-chain alpha-ketoacid dehydrogenase.
Thiamin pyrophosphate is required as an essential cofactor for transketolase which catalyzes the cleavage of a C-C bond in alpha-ketosugars in the hexose monophosphate shunt.
It is also clear that thiamin has a vital role in nerve function, although the biochemical nature of that role is unclear.