an enzyme of the lyase class that takes part in the anaerobic decomposition of carbohydrates in the cells of certain microorganisms, for example, brewer’s yeast, and in the tissues of higher plants. Pyruvate decarboxylase catalyzes the nonoxidative decarboxylation of pyruvic acid, resulting in the formation of acetaldehyde:

CH₃COCOOH → CH₃CHO + CO₂

The reaction proceeds in the presence of thiamine pyrophosphate, which acts as a coenzyme, and of Mg²⁺ ions, which act as cofactors. Pyruvate decarboxylase also decarboxylates other alpha keto acids, for example, α-ketobutyric and α-ketovaleric acids. The activity of the enzyme decreases in proportion to the length of the carbon chain in the substrate.

Pyruvate decarboxylase was discovered in yeast in 1911 by the German biochemist C. Neuberg. It is isolated in pure form from plant tissues, for example, brewer’s yeast and wheat germ; the molecular weight of the wheat-germ variety is about 1,000,000. The term “pyruvate decarboxylase” is also used to designate one of the components of pyruvate dehydrogenase, which catalyzes the oxidative decarboxylation of pyruvic acid with the resultant formation of an acetyl group (CH₃CO—).