Xu5P

Xu5P is the abbreviation for xylulose-5-phosphate, a phosphorylated five-carbon sugar that functions as an intermediate in the pentose phosphate pathway (PPP). It is a central metabolite in cellular carbon metabolism and is found across many organisms.

In biosynthesis and metabolism, Xu5P is produced during the oxidative branch of the PPP. Glucose-6-phosphate is oxidized to ribulose-5-phosphate, which is then converted to xylulose-5-phosphate by the enzyme ribulose-5-phosphate 3-epimerase. This interconversion between ribulose-5-phosphate and Xu5P helps balance the outputs of the oxidative phase with the needs of the non-oxidative phase and glycolysis.

In the non-oxidative phase of the PPP, Xu5P participates in transketolase- and transaldolase-catalyzed reactions that shuffle carbon skeletons among sugar phosphates. For example, Xu5P can react with ribose-5-phosphate to form glyceraldehyde-3-phosphate and sedoheptulose-7-phosphate, and it can also react with glyceraldehyde-3-phosphate to yield fructose-6-phosphate and erythrose-4-phosphate. These reactions help convert pentose phosphates into glycolytic intermediates and into biosynthetic precursors such as ribose-5-phosphate.

Structural and chemical properties of Xu5P include its identity as a ketose phosphate with a phosphate group at the fifth carbon. It is highly polar and negatively charged at physiological pH, enabling interaction with a range of PPP enzymes.

Xu5P is widely referenced in biochemistry and physiology as a key PPP metabolite. Its flux influences the balance between NADPH production, ribose-5-phosphate supply for nucleotide synthesis, and the generation of glycolytic intermediates.

See also: pentose phosphate pathway, ribulose-5-phosphate, glyceraldehyde-3-phosphate, sedoheptulose-7-phosphate.