| GTP | An immediate precursor of guanine nucleotides in RNA; similar to ATP; has a crucial role in microtubule formation. GTP cyclohydrolase, an enzyme that catalyses the reaction of GTP and H2O forming formate and a precursor of tetrahydrobiopterin; a deficiency of this enzyme will result in one form of malignant hyperphenylalaninaemia. Acronym: GTP (05 Mar 2000) |
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| GTP cyclohydrolase | <enzyme> (GTP cyclohydrolase I) or GTP 7,8-8,9-dihydrolase (pyrophosphate-forming) (GTP cyclohydrolase II). An enzyme group that hydrolyzes the imidazole ring of GTP, releasing carbon-8 as formate. Two c-n bonds are hydrolyzed and the pentase unit is isomerised. This is the first step in the synthesis of folic acid from GTP.6 (GTP cyclohydrolase I) and GTP cyclohydrolase II. Chemical name: GTP 7,8-8,9-dihydrolase Registry number: EC 3.5.4.16 (12 Dec 1998) |
| GTP phosphohydrolase | <enzyme> An enzyme that hydrolyzes GTP to GDP and provides energy for peptide chain elongation. Registry number: EC 3.6.1.- (12 Dec 1998) |
| GTP pyrophosphokinase | <enzyme> An enzyme that catalyses reversibly the transfer of a pyrophosphate group from ATP to the 3'-oh group of GDP or GTP with the formation of guanosine 3'-diphosphate 5'-diphosphate or guanosine 3'-diphosphate 5'-triphosphate and AMP. The enzyme, also called stringent factor, is located in the rela gene in stringent strains of bacteria. The above synthesis is induced by mRNA and uncharged trna which is bound to the aminoacyl-t-RNA binding site of the ribosome by a codon-specific association. Chemical name: ATP:GTP 3'-pyrophosphotransferase Registry number: EC 2.7.6.5 (12 Dec 1998) |
| GTP-binding protein | <molecular biology, protein> There are two main classes of G-proteins, the heterotrimeric G proteins that associate with receptors of the seven transmembrane domain superfamily and are involved in signal transduction and the small cytoplasmic G-proteins. Regulatory proteins found in all cells. They are versatile molecular switches, involved in the control of a wide range of biological processes - protein synthesis, signal transduction pathways, growth and differentiation. They all act through a common molecular mechanism based on their ability to bind the guanine nucleotides GTP and GDP selectively and with high affinity. Stimulatory G-proteins are permanently activated by cholera toxin, inhibitory ones by pertussis toxin. Transducin was one of the first of the heterotrimeric G-proteins to be identified. The small G-proteins are a diverse group of monomeric GTPases that include ras, rab, rac and rho and that play an important part in regulating many intracellular processes including cytoskeletal organisation and secretion. Their GTPase activity is regulated by activators (GAPs) and inhibitors (GIPs) that determine the duration of the active state. (12 Jul 2000) |
| GTP-RNA guanylyltransferase | <enzyme> Catalyses addition of GMP residue to 3'-ends of oligonucleotide primers Registry number: EC 2.7.7.- Synonym: terminal guanylyltransferase (26 Jun 1999) |
| GTPase activating protein | <molecular biology> Originally purified as a 125 kD protein from bovine brain (1044 amino acids), stimulates the GTPase activity of ras p21 and thereby switches it to the inactive state. GAP may itself be regulated by phospholipids and by phosphorylation on a tyrosine residue by growth factor receptors (PDGF R, EGF R). The neurofibromatosis type 1 gene NF1) codes for a protein homologous to GAP. GAP has both SH2 and SH3 domains. Another example is sar 1 (from yeast). (18 Nov 1997) |
| phosphoenolpyruvate carboxykinase (GTP) | <enzyme> An enzyme of the lyase class that catalyses the conversion of GTP and oxaloacetate to GDP, phosphoenolpyruvate, and carbon dioxide. This reaction is part of gluconeogenesis in the liver. The enzyme occurs in both the mitochondria and cytosol of mammalian liver. Chemical name: GTP:oxaloacetate carboxy-lyase (transphosphorylating) Registry number: EC 4.1.1.32 (12 Dec 1998) |
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| transducin GTP phosphohydrolase | <enzyme> Stimulated by bovine rhodopsin mutants (asp63 to asn) and (glu134 to gln) with slightly lowered efficiency Registry number: EC 3.6.1.- Synonym: transducin GTPase (26 Jun 1999) |