EC - GTP cyclohydrolase II

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IntEnz Enzyme Nomenclature


Accepted name:
GTP cyclohydrolase II
Other names:
guanosine triphosphate cyclohydrolase II
Systematic name:
GTP 7,8-8,9-dihydrolase (formate-releasing, phosphate-releasing)



The enzyme, found in prokaryotes and some eukaryotes, hydrolytically cleaves the C8-N9 bond of GTP guanine, followed by a subsequent hydrolytic attack at the base, which liberates formate, and cleavage of the α-β phosphodiester bond of the triphosphate to form diphosphate. The enzyme continues with a slow cleavage of the diphosphate to form two phosphate ions. The enzyme requires zinc and magnesium ions for the cleavage reactions at the GTP guanine and triphosphate sites, respectively. It is one of the enzymes required for flavin biosynthesis in many bacterial species, lower eukaryotes, and plants. Cf. EC, GTP cyclohydrolase I, EC, GTP cyclohydrolase IIa, and EC, GTP cyclohydrolase IV.

Links to other databases

Enzymes and pathways: NC-IUBMB , BRENDA , ExplorEnz , ENZYME@ExPASy , KEGG , MetaCyc , UniPathway
Structural data: CSA , EC2PDB
Gene Ontology: GO:0003935
UniProtKB/Swiss-Prot: (221) [show] [UniProt]


  1. Foor, F. and Brown, G.M.
    Purification and properties of guanosine triphosphate cyclohydrolase II from Escherichia coli.
    J. Biol. Chem. 250 : 3545-3551 (1975). [PMID: 235552]
  2. Smith, M. M., Beaupre, B. A., Fourozesh, D. C., Meneely, K. M., Lamb, A. L., Moran, G. R.
    Finding Ways to Relax: A Revisionistic Analysis of the Chemistry of E. coli GTP Cyclohydrolase II.
    Biochemistry 60 : 3027-3039 (2021). [PMID: 34569786]

[EC created 1984]