GTP cyclohydrolases are enzymes that catalyze

imidazole Imidazole (ImH) is an organic compound with the formula C3N2H4. It is a white or colourless solid that is soluble in water, producing a mildly alkaline solution. In chemistry, it is an aromatic heterocycle, classified as a diazole, and has non ...

ring opening of

guanosine triphosphate Guanosine-5'-triphosphate (GTP) is a purine nucleoside triphosphate. It is one of the building blocks needed for the synthesis of RNA during the transcription process. Its structure is similar to that of the guanosine nucleoside, the only ...

(GTP). This reaction is the

committed step In enzymology, the committed step (also known as the ''first'' committed step) is an effectively irreversible enzymatic reaction that occurs at a branch point during the biosynthesis of some molecules. As the name implies, after this step, the mol ...

in the biosynthesis of multiple

coenzymes A cofactor is a non-protein chemical compound or metallic ion that is required for an enzyme's role as a catalyst (a catalyst is a substance that increases the rate of a chemical reaction). Cofactors can be considered "helper molecules" that ass ...

(such as

riboflavin Riboflavin, also known as vitamin B2, is a vitamin found in food and sold as a dietary supplement. It is essential to the formation of two major coenzymes, flavin mononucleotide and flavin adenine dinucleotide. These coenzymes are involved in e ...

and

folate Folate, also known as vitamin B9 and folacin, is one of the B vitamins. Manufactured folic acid, which is converted into folate by the body, is used as a dietary supplement and in food fortification as it is more stable during processing and ...

), tRNA bases, and the phytotoxin toxoflavin. Several GTP cyclohydrolases exist, which sometimes synthesize different products for different pruposes: *

GTP cyclohydrolase I GTP cyclohydrolase I (GTPCH) () is a member of the GTP cyclohydrolase family of enzymes. GTPCH is part of the folate and biopterin biosynthesis pathways. It is responsible for the hydrolysis of guanosine triphosphate (GTP) to form 7,8-dihydrone ...

, part of the

tetrahydrobiopterin Tetrahydrobiopterin (BH4, THB), also known as sapropterin (INN), is a cofactor of the three aromatic amino acid hydroxylase enzymes, used in the degradation of amino acid phenylalanine and in the biosynthesis of the neurotransmitters seroto ...

tetrahydrofolate Tetrahydrofolic acid (THFA), or tetrahydrofolate, is a folic acid derivative. Metabolism Human synthesis Tetrahydrofolic acid is produced from dihydrofolic acid by dihydrofolate reductase. This reaction is inhibited by methotrexate. It is ...

queuosine Queuosine is a modified nucleoside that is present in certain tRNAs in bacteria and eukaryotes. It contains the nucleobase queuine. Originally identified in ''E. coli'', queuosine was found to occupy the first anticodon position of tRNAs for ...

and other biosynthetic pathways * GTP cyclohydrolase Ia, * GTP cyclohydrolase Ib, part of the tetrahydrobiopterin, tetrahydrofolate, queueosine and other biosynthetic pathways *

GTP cyclohydrolase II In enzymology, a GTP cyclohydrolase II () is an enzyme that catalyzes the chemical reaction :GTP + 3 H2O \rightleftharpoons formate + 2,5-diamino-6-hydroxy-4-(5-phosphoribosylamino)pyrimidine + diphosphate Thus, the two substrates of this enzyme ...

, part of the

and toxoflavin biosynthetic pathways *

GTP cyclohydrolase IIa In enzymology, a GTP cyclohydrolase IIa () is an enzyme that catalyzes the chemical reaction :GTP + 3 H2O \rightleftharpoons 2-amino-5-formylamino-6-(5-phosphoribosylamino)pyrimidin-4(3H)-one + 2 phosphate Thus, the two substrates of this enzyme ...

(or GTP cyclohydrolase III{{Cite web , title=ENZYME - 3.5.4.29 GTP cyclohydrolase IIa , url=https://enzyme.expasy.org/EC/3.5.4.29 , access-date=2023-01-23 , website=enzyme.expasy.org), part of the riboflavin and

deazaflavin Coenzyme F420 or 8-hydroxy-5-deazaflavin is a coenzyme (sometimes called a cofactor) involved in redox reactions in methanogens, in many Actinomycetota, and sporadically in other bacterial lineages. It is a flavin derivative. The coenzyme is a ...

cofactor biosynthetic pathways * GTP cyclohydrolase IV * GTP cyclohydrolase MptA, GTP cyclohydrolase Ib paralog These enzymes require divalent

cations An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

for catalysis.

References

EC 3.5.4 Hydrolases