Hydrolases;
Acting on carbon-nitrogen bonds, other than peptide bonds;
In cyclic amidines
BRITE hierarchy

GTP 7,8-8,9-dihydrolase (formate-releasing, phosphate-releasing)

GTP + 4 H2O = formate + 2,5-diamino-6-hydroxy-4-(5-phospho-D-ribosylamino)pyrimidine + 2 phosphate [RN:R00425]

R00425
Reaction

GTP [CPD:C00044];
H2O [CPD:C00001]

The enzyme, found in prokaryotes and some eukaryotes, hydrolytically cleaves the C-N bond at positions 8 and 9 of GTP guanine, followed by a subsequent hydrolytic attack at the base, which liberates formate, and cleavage of the alpha-beta 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 3.5.4.16, GTP cyclohydrolase I, EC 3.5.4.29, GTP cyclohydrolase IIa, and EC 3.5.4.39, GTP cyclohydrolase IV.

EC 3.5.4.25 created 1984, modified 2011, modified 2022