a 2-oxocarboxylate + H(+) = an aldehyde + CO2 Binds 1 metal ion per subunit. Binds 1 thiamine pyrophosphate per subunit. Homotetramer. Expressed in shoots and at lowe levels in roots, flowers and siliques. By abscisic acid (ABA), salt and osmotic stress. Not induced by anoxia. Belongs to the TPP enzyme family.