OH OH Two main classes of aldolases are found in Nature. Type I aldolases activate the nucleophilic partner by forming an imine as an intermediate; this type of enzyme is found in animals and higher plants. Type II aldolases occur in microorganisms and they require R 2 to be a hydroxy group. These enzymes feature a Zn 2+ ion that promotes the reaction by forming a chelate with both the carbonyl and an α-hydroxy group on the nucleophilic partner. Aldolases are highly stereoselective; the particular absolute and relative stereochemistry shown below is just for illustration. Aldolases perform many important metabolic reactions, in both the forward and reverse directions. OH fructose bisphosphate aldolase β-D-fructose-1,6-phosphate D-glyceraldehyde 3-phosphate dihydroxyacetone phosphate NH 2 glycine acetaldehyde pyruvate phosphoenolpyruvate dihydroxyacetone(phosphate) Aldolases will accept a wide variety of aldehydes as electrophiles, but the scope of the nucleophilic partner is usually limited to the natural substrate or a very close analog. * denotes stereocenter formed An engineered aldolase is being used on an industrial scale to produce the side chain of the statin drugs, widely prescribed for reducing the risk of cardiovascular issues.