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In enzymology, a GTP cyclohydrolase II (EC 3.5.4.25) is an enzyme that catalyzes the chemical reaction

GTP + 3 H₂O ${\displaystyle \rightleftharpoons }$ formate + 2,5-diamino-6-hydroxy-4-(5-phosphoribosylamino)pyrimidine + diphosphate

Thus, the two substrates of this enzyme are GTP and H₂O, whereas its 3 products are formate, 2,5-diamino-6-hydroxy-4-(5-phosphoribosylamino)pyrimidine, and diphosphate.

This enzyme belongs to the family of hydrolases, those acting on carbon-nitrogen bonds other than peptide bonds, specifically in cyclic amidines. The systematic name of this enzyme class is GTP 7,8-8,9-dihydrolase (diphosphate-forming). Other names in common use include guanosine triphosphate cyclohydrolase II, and GTP-8-formylhydrolase. This enzyme participates in riboflavin metabolism.

Structural studies

As of late 2007, two structures have been solved for this class of enzymes, with PDB accession codes 2BZ0 and 2BZ1.

References

• Foor F, Brown GM (1975). "Purification and properties of guanosine triphosphate cyclohydrolase II from Escherichia coli". J. Biol. Chem. 250 (9): 3545–51. doi:10.1016/S0021-9258(19)41549-4. PMID 235552.

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