Dribulose5phosphate

D-ribulose-5-phosphate, commonly referred to as ribulose-5-phosphate, is a phosphorylated five-carbon ketose sugar that serves as an intermediate in the pentose phosphate pathway (PPP). It is the product of the oxidative phase of the PPP, formed when 6-phosphogluconate is converted to ribulose-5-phosphate with release of carbon dioxide.

In metabolism, ribulose-5-phosphate can be channeled into different branches of the PPP. It is interconvertible with ribose-5-phosphate by ribulose-5-phosphate isomerase, and can also be converted to xylulose-5-phosphate by ribulose-5-phosphate 3-epimerase. These interconversions feed the non-oxidative branch, where transketolase and transaldolase catalyze carbon skeleton rearrangements. Through these reactions, ribulose-5-phosphate derivatives contribute to the production of glyceraldehyde-3-phosphate and fructose-6-phosphate, which feed into glycolysis, nucleotide biosynthesis, and other anabolic pathways.

Chemically, ribulose-5-phosphate is a D- configured pentulose phosphate, with a phosphate group attached to the fifth carbon. It is typically present transiently in cells, shuttled between enzymes of the PPP according to the cellular demand for NADPH, ribose-5-phosphate for nucleotide synthesis, and biosynthetic precursors for energy metabolism.

See also ribulose-5-phosphate isomerase, ribulose-5-phosphate 3-epimerase, transketolase, transaldolase, and the broader pentose phosphate pathway.