Ribose-5-Phosphate

Ribose-5-phosphate (R5P) is a five-carbon sugar phosphate that functions as an important intermediate in cellular metabolism. Chemically, it consists of ribose with a phosphate group attached to its fifth carbon. Its best-known role is providing the ribose framework needed for nucleotide synthesis .^1,2

Ribose-5-phosphate is produced through the pentose phosphate pathway. In the oxidative phase, glucose-6-phosphate is converted to ribulose-5-phosphate while NADPH is generated, and ribulose-5-phosphate can then be converted into ribose-5-phosphate. Reversible reactions of the nonoxidative phase can also generate R5P from intermediates shared with glycolysis, allowing cells to adjust production according to their relative needs for ribose-5-phosphate and NADPH .²

For nucleotide synthesis, R5P is converted into 5-phosphoribosyl-1-pyrophosphate (PRPP). PRPP provides an activated ribose-phosphate group used in both de novo nucleotide synthesis, in which nucleotides are built from smaller precursors, and salvage pathways, which recycle preformed nitrogenous bases .^2,3

Ribose-5-phosphate should not be confused with ribulose-5-phosphate. Both are five-carbon sugar phosphates in the pentose phosphate pathway, but ribose is an aldose sugar whereas ribulose is a ketose. An isomerase can reversibly convert ribulose-5-phosphate and ribose-5-phosphate into one another .²