Aldol Reactions in Nature

So far, we have examined the non-enzymatic reaction of an aldehyde or ketone with itself (a so-called 'self-condensation' reaction, where 'condensation' means the formation of one larger molecule from two smaller ones). However, aldol reactions occur in several biological pathways, most commonly in the metabolism of carbohydrates (sugars). The enzymes that catalyze aldol reactions are called, not surprisingly, 'aldolases'. They occur in all organisms, but note that Class I aldoases are usually found in animals and higher plants, while Class II aldoases normally appear in bacteria and fungi.