IUBMB Enzyme Nomenclature


Accepted name: 6-phospho-3-hexuloisomerase

Reaction: D-arabino-hex-3-ulose 6-phosphate = D-fructose 6-phosphate

For diagram of reaction, click here

Other name(s): 3-hexulose-6-phosphate isomerase; phospho-3-hexuloisomerase; PHI; 6-phospho-3-hexulose isomerase; YckF

Systematic name: D-arabino-3-hexulose-6-phosphate isomerase

Comments: This enzyme, along with EC, 3-hexulose-6-phosphate synthase, plays a key role in the ribulose-monophosphate cycle of formaldehyde fixation, which is present in many microorganisms that are capable of utilizing C1-compounds [1]. The hyperthermophilic and anaerobic archaeon Pyrococcus horikoshii OT3 constitutively produces a bifunctional enzyme that sequentially catalyses the reactions of EC (3-hexulose-6-phosphate synthase) and this enzyme [4].

Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, PDB, CAS registry number:


1. Ferenci, T., Strøm, T. and Quayle, J.R. Purification and properties of 3-hexulose phosphate synthase and phospho-3-hexuloisomerase from Methylococcus capsulatus. Biochem. J. 144 (1974) 477-486. [PMID: 4219834]

2. Yurimoto, H., Kato, N. and Sakai, Y. Assimilation, dissimilation, and detoxification of formaldehyde, a central metabolic intermediate of methylotrophic metabolism. Chem. Rec. 5 (2005) 367-375. [PMID: 16278835]

3. Kato, N., Yurimoto, H. and Thauer, R.K. The physiological role of the ribulose monophosphate pathway in bacteria and archaea. Biosci. Biotechnol. Biochem. 70 (2006) 10-21. [PMID: 16428816]

4. Orita, I., Yurimoto, H., Hirai, R., Kawarabayasi, Y., Sakai, Y. and Kato, N. The archaeon Pyrococcus horikoshii possesses a bifunctional enzyme for formaldehyde fixation via the ribulose monophosphate pathway. J. Bacteriol. 187 (2005) 3636-3642. [PMID: 15901685]

5. Martinez-Cruz, L.A., Dreyer, M.K., Boisvert, D.C., Yokota, H., Martinez-Chantar, M.L., Kim, R. and Kim, S.H. Crystal structure of MJ1247 protein from M. jannaschii at 2.0 Å resolution infers a molecular function of 3-hexulose-6-phosphate isomerase. Structure 10 (2002) 195-204. [PMID: 11839305]

6. Taylor, E.J., Charnock, S.J., Colby, J., Davies, G.J. and Black, G.W. Cloning, purification and characterization of the 6-phospho-3-hexulose isomerase YckF from Bacillus subtilis. Acta Crystallogr. D Biol. Crystallogr. 57 (2001) 1138-1140. [PMID: 11468398]

[EC created 2008]

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