EC - GTP cyclohydrolase IIa

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IntEnz Enzyme Nomenclature


Accepted name:
GTP cyclohydrolase IIa
Other name:
GTP cyclohydrolase III
Systematic name:
GTP 8,9-dihydrolase (phosphate-forming)




Requires Mg2+. This enzyme catalyses the hydrolysis of the imidazole ring of guanosine 5'-triphosphate, N7-methylguanosine 5'-triphosphate or inosine 5'-triphosphate. Xanthosine 5'-triphosphate and ATP are not substrates. It also catalyses the hydrolysis of diphosphate to form two equivalents of phosphate. Unlike GTP cyclohydrolase II (EC, this enzyme does not release formate, but does hydrolyze the diphosphate from GTP to phosphate.

Links to other databases

Enzymes and pathways: NC-IUBMB , BRENDA , DIAGRAM , ExplorEnz , ENZYME@ExPASy , KEGG , MetaCyc , UniPathway
Structural data: CSA , EC2PDB
Gene Ontology: GO:0043740
UniProtKB/Swiss-Prot: (27) [show] [UniProt]


  1. Graham, D.E., Xu, H. and White, R.H.
    A member of a new class of GTP cyclohydrolases produces formylaminopyrimidine nucleotide monophosphates.
    Biochemistry 41: 15074-15084 (2002). [PMID: 12475257]

[EC created 2003]