Transaldolase

Transaldolase is an enzyme of the pentose phosphate pathway. Transaldolase has a Lys residue in the active site, which forms a Schiff base with the keto group in sedoheptulose-7-phosphate. The reaction mechanism is similar to the reverse reaction catalyzed by aldolase: the bond joining carbons 3 and 4 is split, leaving dihydroxyacetone joined to the enzyme via a Schiff base. This cleavage reaction generates the unusual aldose sugar erythrose-4-phosphate. Then transaldolase catalyzes the condensation of glyceraldehyde-3-phosphate with the Schiff base of dihydroxyacetone, yielding enzyme bound fructose-6-phosphate. Hydrolysis of the Schiff base liberates free fructose-6-phosphate, one of the products of the pentose phosphate pathway.