Schiff base
The generic fructose bisphosphate aldolase enzyme cleaves a 6-carbon fructose sugar into two 3-carbon products in a reverse aldol reaction. This reaction is typified by the formation of a Schiff base intermediate with a lysine residue (lysine 229) in the active site of the enzyme; the formation of a Schiff base is the key differentiator between Class I (produced by animals) and Class II (produced by fungi and bacteria) aldolases. After Schiff base formation, the fourth hydroxyl group on the fructose backbone is then deprotonated by an aspartate residue (aspartate 33), which results in an aldol cleavage. Schiff base hydrolysis yields two 3-carbon products. Depending on the reactant, F1P or FBP, the products are DHAP and glyceraldehyde or glyceraldehyde 3-phosphate, respectively.