transketolasen

Transketolase, sometimes referred to as transketolasen in some languages, is a cytosolic enzyme that depends on thiamine pyrophosphate (TPP) and magnesium ions as cofactors. It belongs to the family of transferases and catalyzes the transfer of two-carbon units in the non-oxidative branch of the pentose phosphate pathway (PPP). Its Enzyme Commission number is 2.2.1.7.

In the non-oxidative PPP, transketolase transfers two-carbon fragments from ketose donors to aldose acceptors. The canonical reactions include transferring a two-carbon unit from xylulose-5-phosphate to ribose-5-phosphate to form glyceraldehyde-3-phosphate and sedoheptulose-7-phosphate, and transferring a two-carbon unit from xylulose-5-phosphate to erythrose-4-phosphate to yield glyceraldehyde-3-phosphate and fructose-6-phosphate. Through these reactions, transketolase enables the interconversion of sugar phosphates, linking the PPP with glycolysis and nucleotide biosynthesis.

Biological role: Transketolase helps regenerate glycolytic intermediates and provides ribose-5-phosphate for nucleotide and nucleic acid synthesis. By operating in the non-oxidative PPP, it complements the oxidative phase that generates NADPH, contributing to cellular redox balance and metabolic flexibility across tissues.

Clinical and diagnostic notes: Because transketolase is thiamine-dependent, its activity is sensitive to thiamine status. Assessment of transketolase activity, often in red blood cells, and the thiamine pyrophosphate effect are used to evaluate thiamine deficiency. Impaired transketolase function is associated with conditions such as Wernicke–Korsakoff syndrome, highlighting the enzyme’s importance in human metabolism.