ID 3.5.4.29 DE GTP cyclohydrolase IIa. AN GTP cyclohydrolase III. CA GTP + 3 H2O = 2-amino-5-formylamino-6-(5-phospho-D- CA ribosylamino)pyrimidin-4(3H)-one + 2 H(+) + 2 phosphate. CC -!- This enzyme catalyzes the hydrolysis of the imidazole ring of CC guanosine 5'-triphosphate, N(7)-methylguanosine 5'-triphosphate or CC inosine 5'-triphosphate. CC -!- Xanthosine 5'-triphosphate and ATP are not substrates. CC -!- It also catalyzes the hydrolysis of diphosphate to form two CC equivalents of phosphate. CC -!- Unlike EC 3.5.4.25, this enzyme does not release formate, but does CC hydrolyze the diphosphate from GTP to phosphate. DR Q9HQT7, GCH31_HALSA; Q9HQS9, GCH32_HALSA; Q9YC89, GCH3_AERPE ; DR B9LRB1, GCH3_HALLT ; Q57609, GCH3_METJA ; A4FZ97, GCH3_METM5 ; DR A9A6P4, GCH3_METM6 ; A6VJ40, GCH3_METM7 ; Q6M066, GCH3_METMP ; DR A5ULV0, GCH3_METS3 ; Q2NEH8, GCH3_METST ; O27096, GCH3_METTH ; DR A6US18, GCH3_METVS ; Q3INZ0, GCH3_NATPD ; Q8ZU20, GCH3_PYRAE ; DR A4WKJ7, GCH3_PYRAR ; A3MV81, GCH3_PYRCJ ; A1RRI0, GCH3_PYRIL ; DR B1YAW1, GCH3_PYRNV ; Q980B6, GCH3_SACS2 ; C3MZ63, GCH3_SULIA ; DR C4KIE1, GCH3_SULIK ; C3MR15, GCH3_SULIL ; C3MX03, GCH3_SULIM ; DR C3NGF2, GCH3_SULIN ; C3N783, GCH3_SULIY ; Q975M4, GCH3_SULTO ; //