Thiamine (Ia), in the form of its pyrophosphate, cocarboxylase (Ib), is the coenzyme for a number of important biochemical reactions, including the decarboxylation of pyruvic acid to acetaldehyde, the conversion of pyruvic acid to acetoin and the transketolase reaction; it is also involved in the oxidative decarboxylation of pyruvic acid to “active acetate.''