xylulose5fosfat

Xylulose-5-phosphate is a phosphorylated ketose sugar, a five-carbon sugar phosphate in which a phosphate group is attached to the fifth carbon of D-xylulose. It is an important intermediate in the pentose phosphate pathway (PPP), where it participates in the non-oxidative phase and helps link carbohydrate metabolism to nucleotide biosynthesis and redox balance.

In the oxidative phase of the PPP, glucose-6-phosphate is oxidized, generating NADPH and producing ribulose-5-phosphate. This intermediate can be isomerized to ribose-5-phosphate or epimerized to xylulose-5-phosphate by ribulose-5-phosphate 3-epimerase. Xylulose-5-phosphate then serves as a substrate for transketolase in the non-oxidative branch.

Transketolase transfers two-carbon units from xylulose-5-phosphate to aldose phosphates. The two principal reactions are: xylulose-5-phosphate plus ribose-5-phosphate yields glyceraldehyde-3-phosphate and sedoheptulose-7-phosphate; and xylulose-5-phosphate plus erythrose-4-phosphate yields glyceraldehyde-3-phosphate and fructose-6-phosphate. These reactions rearrange carbon skeletons, enabling production of glycolytic intermediates and intermediates for nucleotide synthesis.

Biological significance: xylulose-5-phosphate is a key carrier in the PPP, facilitating the interconversion of sugar phosphates and supporting NADPH production, ribose-5-phosphate generation, and integration with glycolysis. It is a conserved intermediate found across bacteria, plants, and animals as part of the cellular carbohydrate metabolism network.