IUBMB Enzyme Nomenclature


Accepted name: GTP cyclohydrolase IIa

Reaction: GTP + 3 H2O = 2-amino-5-formylamino-6-(5-phospho-D-ribosylamino)pyrimidin-4(3H)-one + 2 phosphate

For diagram of reaction, click here

Systematic name: GTP 8,9-hydrolase (phosphate-forming)

Comments: 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 hydrolyse the diphosphate from GTP to phosphate.

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


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 (2002) 15074-15084. [PMID: 12475257]

[EC created 2003, modified 2011]

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