transaldolase

Transaldolase is an enzyme that plays a crucial role in the pentose phosphate pathway. This metabolic pathway is responsible for generating NADPH and precursor molecules for nucleotide synthesis. Transaldolase catalyzes the reversible transfer of a three-carbon fragment (dihydroxyacetone) from fructose-6-phosphate to glyceraldehyde-3-phosphate. This reaction forms erythrose-4-phosphate and xylulose-5-phosphate. Specifically, transaldolase belongs to the family of lyases, which are enzymes that catalyze the cleavage of a chemical bond by an elimination reaction, other than hydrolysis, to leave a double bond or a ring structure.

The enzyme's mechanism involves the formation of a Schiff base intermediate with a lysine residue in its active site. This intermediate facilitates the transfer of the dihydroxyacetone moiety. Transaldolase is particularly important in organisms that utilize the Calvin cycle for carbon fixation, such as plants and cyanobacteria, where it contributes to the regeneration of ribulose-1,5-bisphosphate, a key acceptor of carbon dioxide. In mammals, transaldolase is also present and contributes to carbohydrate metabolism, although its specific roles can vary across tissues and physiological conditions. Defects in transaldolase activity have been linked to certain metabolic disorders, highlighting its importance in cellular homeostasis.