In enzymology, a ribose 1,5-bisphosphate phosphokinase (EC 2.7.4.23) is an enzyme that catalyzes the chemical reaction

ATP + ribose 1,5-bisphosphate ${\displaystyle \rightleftharpoons }$ ADP + 5-phospho-alpha-D-ribose 1-diphosphate

Thus, the two substrates of this enzyme are ATP and ribose 1,5-bisphosphate, whereas its two products are ADP and 5-phospho-alpha-D-ribose 1-diphosphate.

This enzyme belongs to the family of transferases, specifically those transferring phosphorus-containing groups (phosphotransferases) with a phosphate group as acceptor. The systematic name of this enzyme class is ATP:ribose-1,5-bisphosphate phosphotransferase. Other names in common use include ribose 1,5-bisphosphokinase, and PhnN. This enzyme participates in pentose phosphate pathway.

• Hove-Jensen B, Rosenkrantz TJ, Haldimann A, Wanner BL (2003). "Escherichia coli phnN, encoding ribose 1,5-bisphosphokinase activity (phosphoribosyl diphosphate forming): dual role in phosphonate degradation and NAD biosynthesis pathways". J. Bacteriol. 185 (9): 2793–801. doi:10.1128/JB.185.9.2793-2801.2003. PMC 154390. PMID 12700258.