Re: How does thiamin hydrochloride work as a coenzyme in cellular respiration?

Thiamine or Vitamin B1 is an important cofactor in the Krebs or citric 
acid cycle which takes place in the mitochondria.  Before thiamine is 
incorporated into the enzymes pyruvate dehydrogenase and alpha-
ketogluterate dehydrogenase, the pyrophosphate group is added to thiamine 
to make thiamine pyrophosphate.  It is this molecule that participates 
along with other cofactors in the catalytic oxidative decarboxylation of 
pyruvate (a product of glycolysis) to form acetyl CoA.  Acetyl CoA then 
enters the citric acid cycle and ultimately produces NADH and FADH2 which 
then participate in the electon transport chain.

Stryer, Lubert,  Biochemistry,  3rd edition, 1988, Chapter 16