Transformylase

Aminoimidazole-4-Carboxamide Ribonucleotide Transformylase Carbonic Anhydrase II DNA Gyrase... 

Aminoinnidazole-4-carboxannide ribonucleotide (AlCAR) transformylase inhibitor, 1C 50 = 4.1. M... 

Li C, Xu L, Wolan DW, Wilson lA, Olson AJ. Virtual screening of human 5-aminoimidazole-4-carboxamide ribonucleotide transformylase against the NCI diversity set by use of AutoDock to identify novel nonfolate inhibitors. J Med Chem 2004 47 6681-90. 

Benkovic SJ The transformylase enzymes in de novo purine biosynthesis. Trends Biochem Sci 1994 9 320. 

Equation 1 is catalyzed by glycinamide ribotide (GAR) trans-formylase and Equation 2 is catalyzed by aminoimidazole-carboxamide ribotide (AICAR) transformylase. 

MTX also has several effects on the purine synthetic pathway. MTXPGs inhibit the enzyme aminoimidazole carboxamide ribonucleotide (AlCAR) transformylase, which in turn causes intracellular accumulation of AICAR. AICAR and its metabolites can then inhibit two enzymes in the adenosine pathway adenosine deaminase and adenosine monophosphate (AMP) deaminase, which leads to intracellnlar accumulation of adenosine and adenine nucleotides. Subsequent dephosphorylation of these nucleotides results in increased extracellular concentrations of adenosine, which is a powerful anti-inflammatory agent (11). 

Fig. 14.1 Cellular pathway of methotrexate. ABCBl, ABCCl-4, ABC transporters ADA, adenosine deaminase ADP, adenosine diphosphate AICAR, aminoimidazole carboxamide ribonucleotide AMP, adenosine monophosphate ATIC, AICAR transformylase ATP, adenosine triphosphate SjlO-CH -THF, 5,10-methylene tetrahydrofolate 5-CHj-THF, 5-methyl tetrahydro-folate DHFR, dihydrofolate reductase dTMP, deoxythymidine monophosphate dUMP, deoxy-uridine monophosphate FAICAR, 10-formyl AICAR FH, dihydrofolate FPGS, folylpolyglutamyl synthase GGH, y-glutamyl hydrolase IMP, inosine monophosphate MTHFR, methylene tetrahydrofolate reductase MTR, methyl tetrahydrofolate reductase MTX-PG, methotrexate polyglutamate RFCl, reduced folate carrier 1 TYMS, thymidylate synthase. Italicized genes have been targets of pharmacogenetic analyses in studies published so far. (Reproduced from ref. 73 by permission of John Wiley and Sons Inc.)...

Dervieux, T., Eurst, D., Lein, D. O., et al. (2004) Polyglutamation of methotrexate with common polymorphisms in reduced folate carrier, aminoimidazole carboxamide ribonucleotide transformylase, and thymidylate synthase are associated with methotrexate effects in rheumatoid arthritis. Arthritis and Rheumatism. 50, 2766-2774. 

This enzyme [EC 2.1.2.2], also known as 5 -phosphoribo-sylglycinamide transformylase, catalyzes the reaction of 10-formyltetrahydrofolate with 5 -phosphoribosylglyci-namide to produce tetrahydrofolate and 5 -phosphoribo-syl-A -formylglycinamide. 

OXALYL-CoA DECARBOXYLASE N-Formylglutamate transformylase, GLUTAMATE FORMYLTRANSFERASE FORMYLGLYCINAMIDE RIBONUCLEOTIDE AMIDOTRANSFERASE FORMYLGLYCINAMIDINE SYNTHETASE... 

Glycinamide ribonucleotide transformylase (GAR Tfase) is a folate-dependent enzyme essential to the de novo purine biosynthetic pathway. It utilizes the cofactor 10-formyl tetrahydrofohc acid (10-formyl-THF) to transfer a formyl group to the primary amine of its substrate a-glycinamide ribonucleotide. Potent, and potentially selective, inhibitors of GARTfase and de novo purine biosynthesis have been shown to be promising as antitumor drugs. 

Methotrexate s principal mechanism of action at the low doses used in the rheumatic diseases probably relates to inhibition of aminoimidazolecarboxamide ribonucleotide (AICAR) transformylase and thymidylate synthetase, with secondary effects on polymorphonuclear chemotaxis. There is some effect on dihydrofolate reductase and this affects lymphocyte and macrophage function, but this is not its principal mechanism of action. Methotrexate has direct inhibitory effects on proliferation and stimulates apoptosis in immune-inflammatory cells. Additionally, inhibition of proinflammatory cytokines linked to rheumatoid synovitis has been shown, leading to decreased inflammation seen with rheumatoid arthritis. 

SAICAR synthetase SAICAR lyase AICAR transformylase (jj) IMP synthase... 

Next, a transformylase transfers a formyl group from Af10-formyltetrahydrofolate to the amino group of the Met residue ... 

The transformylase is more selective than the Met-tRNA synthetase it is specific for Met residues attached to tRNAfMet, presumably recognizing some unique structural feature of that tRNA. By contrast, Met-tRNAMet inserts methionine in interior positions in polypeptides. 

Addition of the AT-formyl group to the amino group of methionine by the transformylase prevents fMet from entering interior positions in a polypeptide while also allowing fMet-tRNAfMet to be bound at a specific ribo-somal initiation site that accepts neither Met-tRNAMet nor any other aminoacyl-tRNA. 

Fig. 2. Enzyme catalysis by glycinaminde ribonucleotide transformylase (GAR TFase). (a) Transfer of the formyl group from (13) to (12) to form 2-(formylamino)- jV-(5-0-phosphono-p-D-ribofuranosyl acetamide [349-34-8] (14) and (b) multisubstrate inhibitor (15).

Directly coupled HPLC-NMR spectroscopy has been used in a number of other studies of chemical impurities. An impurity in a bulk drug sample of the glycinamide ribonucleotide transformylase inhibitor AG2034, shown below ... 

Aimi,J., Qiu, H., Williams, J., Zalkin, H., and Dixon, J. E. (1990). De novo purine nucleotide biosynthesis cloning of human and avian cDNAs encoding the trifunctional glycinam-ide ribonucleotide synthetase-aminoimidazole ribonucleotide synthetase-glycinamide ribonucleotide transformylase by functional complementation in E. colt. Nucleic Acids Res., 18, 6665-6672. 

There are four multifunctional enzymes in the pathway A trifunctional enzyme comprising GAR synthetase, GAR transformylase and AIR synthetase catalyzes reactions 2, 3 and 5 (PRA—> GAR— FGAR, FGAM > AIR Fig. 15-16), respectively. The GAR synthetase and GAR transformylase domains may be separated by digestion of the trifunctional enzyme with the protease, chymotrypsin. 

A bifunctional enzyme, comprising the activities of AIR carboxylase and SAICAR synthetase, catalyzes reactions 6 and 7 of the purine pathway (AIR—> CAIR— SAICAR Fig. 15-16). A second bifunctional enzyme, IMP synthase, containing the activities of AICAR transformylase and IMP cyclohydrolase, catalyzes reactions 9 and 10 of the pathway (AICAR — FAICAR— IMP Fig. 15-16). Human IMP synthase has a subunit molecular weight of 62.1 kDa and associates as a dimer. A... 

Fig. 15-16 The de novo purine biosynthetic pathway. Rib-5-P, ribose 5-phosphate P-Rib-PP, 5-phosphoribosyl 1-pyrophosphate PRA, 5-phosphoribosylamine IO-CHO-FH4, /Vl0-formyl tetrahydrofolate GAR, glycineamide ribotide FGAR. /V-formylglycineamide ribotide FGAM, /V-formylglycineamidine ribotide AIR, 5-aminoimidazole ribotide CAIR, 4-carboxy-5-aminoimidazole ribotide SAICAR, iV-succino-5-aminoimidazole-4-carboxamide ribotide AICAR, 5-aminoimidazole-4-carboxamide ribotide FAICAR, 5-formamidoimidazole-4-carboxamide ribotide sAMP, /V-succino-AMP. Enzymes (1) amido phosphoribosyltransferase (2) GAR synthetase (3) GAR transformylase (4) FGAM synthetase (5) AIR synthetase (6) AIR carboxylase (7) SAICAR synthetase (8) adenylosuecinase (9) AICAR transformylase (10) IMP cyclohydrolase (11) sAMP synthetase (12) adenylosuecinasc (13) IMP dehydrogenase (14) GMP synthetase.

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