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PubMed2004

Expression of cholecystokinin-2/gastrin receptor in the murine pancreas modulates cell adhesion and cell differentiation in vivo.

The presence of gastrin and cholecystokinin-2 (CCK2) receptors in human preneoplastic and neoplastic gastrointestinal lesions suggests a role in cancer development. In addition to the growth-promoting action of gastrin, recently a role of the cholecystokinin-2/gastrin receptor (CCK2-R) modulating cellular morphology in cultured epithelial cells has been shown. Here, we have investigated in transgenic (ElasCCK2) mice whether ectopic expression of human CCK2-R in the exocrine pancreas affected epithelial differentiation. Cellular localization of cell adhesion molecules, differentiation markers, and transcription factors was determined using immunofluorescence techniques. Before tumor formation, expression and subcellular localization of proteins of the adherens junction complex, differentiation markers, and transcription factors were altered in ElasCCK2 exocrine pancreas, indicating an evolution from an acinar to a ductal phenotype. Loss of cell polarity, defective secretion, and loss of intercellular adhesion in acini of ElasCCK2 mice was confirmed by ultrastructural analysis. Finally, expression of the transgene in mice treated with the carcinogen azaserine resulted in enhanced size of preneoplastic lesions as well as an increased degree of acinar-ductal transdifferentiation. Thus, these data represent the first evidence for the CCK2-R modulating intercellular adhesion and cell fate in vivo and show that these alterations may contribute to enhanced sensitivity of ElasCCK2 pancreas to chemical carcinogens.

Animals↗
PubMed2001

Glucosamine enhances platelet-derived growth factor-induced DNA synthesis via phosphatidylinositol 3-kinase pathway in rat aortic smooth muscle cells.

Vascular smooth muscle cells play a key role in the development of atherosclerosis. Culture of vascular smooth muscle A10 cells with high glucose for 4 weeks enhanced platelet-derived growth factor (PDGF)-induced BrdU incorporation. Since a long period of high glucose incubation was required for the effect, and it was inhibited by co-incubation with azaserine, the role of hexosamine biosynthesis in the development of atherosclerosis in diabetes was studied in A10 cells. Addition of glucosamine to the culture media enhanced PDGF-stimulated BrdU incorporation, and PDGF-induced tyrosine phosphorylation of the PDGF beta-receptor was increased by glucosamine treatment. Of the subsequent intracellular signaling pathways, PDGF-induced PDGF beta-receptor association with PLC gamma was not affected, whereas tyrosine phosphorylation of Shc, subsequent association of Shc with Grb2, and MAP kinase activation were relatively decreased. In contrast, PDGF-induced PDGF beta-receptor association with the p85 regulatory subunit of PI3-kinase and PI3-kinase activation were increased by 20% (P<0.01) and 36% (P<0.01), respectively. The intracellular signaling molecules responsible for the glucosamine effect were further examined using pharmacological inhibitors. Pretreatment with PLC inhibitor (U73122) had negligible effects, and MEK1 inhibitor (PD98059) showed only a slight inhibitory effect on the PDGF-induced BrdU incorporation. In contrast, pretreatment with PI3-kinase inhibitor (LY294002) significantly inhibited glucosamine enhancement of PDGF-induced BrdU incorporation. These findings suggest that glucosamine is involved in the development of atherosclerosis by enhancing PDGF-induced mitogenesis specifically via the PI3-kinase pathway.

Adaptor Proteins, Signal Transducing↗
PubMed1981

Reconstitution of binding protein dependent active transport of glutamine in spheroplasts of Escherichia coli.

In order to directly prove that the periplasmic glutamine binding protein is an essential component of the osmotic shock sensitive active transport system for glutamine in Escherichia coli, we demonstrated the reconstitution of binding protein dependent glutamine transport in spheroplasts of that organism. It was shown by arsenate inhibition that the reconstituted transport system was energy dependent, and the use of azaserine, an inhibitor of glutamine-utilizing enzymes, indicated that the restoration of transport by binding protein did not require the metabolizing of the transport substrate. Furthermore, the binding protein dependent transport of glutamine was shown to require at least one other macromolecular component, presumably membrane bound, which was absent in a strain containing a deletion of the genes coding for the glutamine transport system but was present in a strain carrying a mutation only in the structural gene for the glutamine binding protein.

Arsenates↗
PubMed1993

Inhibitory effect of a cholecystokinin antagonist on pancreatic carcinogenesis after pancreatobiliary diversion.

The role of cholecystokinin (CCK) has been explored in pancreatic carcinogenesis following pancreatobiliary diversion (PBD), using the specific CCK receptor antagonist CR-1409. Male Wistar rats (n = 80) weighing 70-100 g were given weekly i.p. injections of azaserine (30 mg kg-1 week-1) for 3 consecutive weeks. One week later animals were randomised to receive either PBD or sham PBD and thereafter to receive s.c. injections of either saline or CR-1409 (10 mg kg-1 day-1, 5 days a week). Six months after operation surviving rats were killed as follows: sham + saline 20, PBD + saline 19, sham + CR-1409 14, PBD + CR-1409 11. Cardiac blood was taken for CCK assay and the pancreas was excised for wet weight measurement and quantitative estimation of atypical acinar cell foci (AACF), the precursor of carcinoma. PBD reduced median body weight (3-20% less than shams) but trebled the absolute and relative pancreatic weights (P < 0.001). CR-1409 blunted this adaptive response to PBD, reducing absolute pancreatic weight by 35% (P < 0.005). PBD quadrupled circulating CCK concentrations, regardless of the antagonist treatment. Acidophilic AACF occurred only in rats with PBD. CR-1409 markedly reduced the number of observed acidophilic AACF by 90% (P < 0.001) and the number of foci per pancreas by 93% (P < 0.001). Moreover, CR-1409 reduced the mean focal diameter of each lesion by 18% (P < 0.005), the mean focal volume by 58% (P < 0.05) and the percentage of pancreas occupied by acidophilic foci by 95% (P < 0.001). PBD enhances pancreatic carcinogenesis by causing hypercholecystokininaemia, and CR-1409 largely inhibits this enhancement.

Animals↗
PubMed1972

Pyrimidine nucleotide biosynthesis in Phaseolus aureus. Enzymic aspects of the control of carbamoyl phosphate synthesis and utilization.

1. Carbamoyl phosphate synthetase activity of Phaseolus aureus extracts was assayed by coupling it to the catalytic subunit of Escherichia coli aspartate transcarbamoylase and determining the [(14)C]carbamoylaspartate so formed. The stability of the activity was improved by the addition of ornithine and dimethyl sulphoxide to the extraction medium. 2. The synthetase activity was found to utilize either glutamine or ammonia as amino donor, the Michaelis constants being 0.17+/-0.03mm and 6.1+/-1.0mm respectively. N-Acetylglutamate did not significantly alter the rate with either substrate, and azaserine inhibited the reaction with both amino donors to the same extent. 3. Ornithine was shown to stimulate the activity, and to counteract inhibition by UMP. The purine nucleotides IMP and GMP enhanced carbamoyl phosphate formation, whereas AMP had an inhibitory effect. 4. The Michaelis constant for carbamoyl phosphate was determined in concentrated extracts for both aspartate transcarbamoylase and ornithine transcarbamoylase activities, and was 0.13+/-0.03mm and 1.58+/-0.16mm respectively. The ratio of the activities of these two enzymes, determined at near-saturating substrate concentrations, was 1:3 (aspartate transcarbamoylase/ornithine transcarbamoylase). 5. It is concluded that in this plant tissue there is one enzyme, carbamoyl phosphate synthetase, supplying carbamoyl phosphate to both the pyrimidine and arginine pathways, that the pyrimidine pathway claims most of the available carbamoyl phosphate (depending on the concentration of the nucleotide effectors) when this intermediate is present at low concentrations; and that when the carbamoyl phosphate concentration is increased, possibly by ornithine stimulation, a larger proportion can be taken up by the arginine pathway.

Adenosine Triphosphate↗
PubMed1983

Purine biosynthesis de novo in rat skeletal muscle.

Purine biosynthesis by the 'de novo' pathway was demonstrated in isolated rat extensor digitorum longus muscle with [1-14C]glycine, [3-14C]serine and sodium [14C]formate as nucleotide precursors. Evidence is presented which suggests that the source of glycine and serine for purine biosynthesis is extracellular rather than intracellular. The relative incorporation rates of the three precursors were formate greater than glycine greater than serine. Over 85% of the label from formate and glycine was recovered in the adenine nucleotides, principally ATP. Azaserine markedly inhibited purine biosynthesis from both formate and glycine. Cycloserine inhibited synthesis from serine, but not from formate. Adenine, hypoxanthine and adenosine markedly inhibited purine synthesis from sodium [14C]formate.

Adenine↗
PubMed1991

Substrate-specificity of glutamine transporters in membrane vesicles from rat liver and skeletal muscle investigated using amino acid analogues.

We investigated the effects of glutamine and histidine analogues on glutamine transport processes in membrane vesicles prepared from rat liver (sinusoidal membrane) and skeletal muscle (sarcolemma). L-[14C]Glutamine is transported in these membranes predominantly by Systems N/Nm (liver and muscle respectively), and to a lesser extent by Systems A and L (e.g. about 60, 20 and 20% of total flux respectively via Systems N, A and L at 0.05 mM-glutamine in liver membrane vesicles). The glutamine anti-metabolites 6-diazo-5-oxo-L-norleucine and acivicin were relatively poor inhibitors of glutamine uptake into liver membrane vesicles (less than 25% inhibition at 20-fold excess) and appeared primarily to inhibit System A activity (i.e. N-methylaminoisobutyric acid-inhibitable glutamine uptake). In similar experiments azaserine (also a glutamine anti-metabolite) inhibited approx. 50% of glutamine uptake, apparently by inhibition of System A and also of System L (i.e. 2-amino-2-carboxybicyclo[2,2,1]heptane-inhibitable glutamine uptake). Glutamate gamma-hydroxamate, aspartate beta-hydroxamate, histidine and N'-methylhistidine were all strong inhibitors of glutamine uptake into liver membrane vesicles (greater than 65% inhibition at 20-fold excess), but neither homoglutamine nor N'-methylhistidine produced inhibition. L-Glutamate-gamma-hydroxamate was shown to be a competitive inhibitor of glutamine transport via System N (Ki approximately 0.6 mM). Glutamine uptake in sarcolemmal vesicles showed a similar general pattern of inhibition as in liver membrane vesicles. The results highlight limits on the substrate tolerance of System N; we suggest that the presence of both an L-alpha-amino acid group and a nitrogen group with a delocalized lone-pair of electrons (amide or pyrrole type), separated by a specific intramolecular distance (C2-C4 chain equivalent), is important for substrate recognition by this transporter.

Amino Acids↗
PubMed1998

Glucosamine induces translocation of protein kinase C isoenzymes in mesangial cells.

Activation of protein kinase C (PKC) has been implicated in the high glucose-induced stimulation of matrix protein production in mesangial cells. Since we have found (Kolm-Litty et al., 1998) that glucosamine, similar to the PKC activator phorbol myristate acetate (PMA), mimicks high glucose-induced TGF-beta1 overexpression and subsequent matrix overproduction, the action of these agents on the translocation of PKC isoenzymes was studied in cultured mesangial cells. Exposure to 12 mM glucosamine resulted in rapid and specific translocation of PKC-isoenzymes in mesangial cells i.e. glucosamine caused an increased and sustained translocation of PKC-alpha, -beta and -epsilon while PKC-zeta was essentially unaffected. Comparison with PMA-induced translocation exhibited distinct differences. Exposure to high glucose concentrations of mesangial cells induced translocation of PKC-beta and down-regulation of PKC-epsilon while PKC-alpha and -zeta were essentially unaltered. Presence of azaserine an inhibitor of glutamine: fructose-6-phosphate amidotransferase, the key enzyme of the hexosamine pathway, attenuated the high glucose-induced effects on the membrane fraction of PKC-beta. Our results indicate that i) glucosamine is a potent stimulator of PKC-translocation exhibiting an isoenzyme specific translocation kinetic which is different from PMA-induced PKC-isoenzyme translocation ii) the hexosamine pathway may be possibly involved in the high glucose-induced activation of PKC.

Animals↗
PubMed1971

Hypoxanthine-guanine phosphoribosyltransferase deficiency: chemical agents selective for mutant or normal cultured fibroblasts in mixed and heterozygote cultures.

Cultured fibroblasts established from skin biopsies from patients with the Lesch-Nyhan syndrome are deficient in hypoxanthine-guanine phosphoribosyl-transferase (EC 2.4.2.8) activity. This deficiency makes possible the use of chemicals that select either for or against deficient variants in cultured fibroblasts. Two-way selection has been achieved by the use of 6-thioguanine, which selects for the deficient mutant, and azaserine, which selects to some extent for the normal allele in mixed cultures, as well as in cultures from heterozygotes. Theoretical considerations predict that the phenomenon of metabolic cooperation would tend to reinforce the former and to weaken the latter type of selection, and this is in accordance with the experimental findings.

Autoradiography↗
PubMed1977

Affinity labeling of gamma-glutamyl transpeptidase and location of the gamma-glutamyl binding site on the light subunit.

Gamma-Glutamyl transpeptidase, which consists of two nonidentical subunits, is rapidly inactivated with respect to its transpeptidase and hydrolase activities by the gamma-glutamyl analogs 6-diazo-5-oxo-L-norleucine and L-azaserine. Inactivation, which is prevented by gamma-glutamyl substrates (but not by acceptor substrates), is accelerated by maleate, which was previously shown to enhance utilization of glutamine by transpeptidase. 6-Diazo-5-oxo--norleucine reacts specifically, covalently, and stoichiometrically at the gamma-glutamyl site of the enzyme, which was localized through studies with 6-diazo-5-OXO-[14C]norleucine to the light subunits of both the transpeptidase of rat kidney (which has subunits of molecular weights 22,000 and 46,000) and the transpeptidase of human kidney (which has subunits of molecular weights 22,000 and 62,000). The findings, which indicate that these enzymes have similar gamma-glutamyl binding subunits, are relevant to the structure-function relationships of this membrane-bound enzyme and its physiological role.

Affinity Labels↗
PubMed1978

Serine-borate complex as a transition-state inhibitor of gamma-glutamyl transpeptidase.

gamma-Glutamyl transpeptidase, a membrane-bound enzyme, functions in the gamma-glutamyl cycle to catalyze utilization of glutathione. It has been postulated that the amino-acid-stimulated utilization of glutathione by gamma-glutamyl transpeptidase reflects an aspect of amino acid translocation. As one approach to the effective in vivo inhibition of this enzyme, the inhibition of the enzyme by L-serine in the presence of borate buffers [Revel, J.P. & Ball, E.G. (1959) J. Biol. Chem. 234, 577-582] was reinvestigated. Inhibition by L-serine, D-serine, and alpha-methyl-DL-serine in the presence of borate is competitive with respect to gamma-glutamyl substrate and such inhibition is parallel to the activity of transpeptidase toward L-gamma-glutamyl, D-gamma-glutamyl, and L-gamma-(alpha-methyl)glutamyl derivatives. L-Serine and borate effectively protect against inactivation of the enzyme by the gamma-glutamyl analogs, 6-diazo-5-oxonorleucine and azaserine, which bind to the gamma-glutamyl site of the enzyme. These studies, kinetic investigations, equilibrium dialysis experiments, and other data support the view that inhibition is produced by formation of serine-borate complex which binds at the gamma-glutamyl binding site of the light subunit of gamma-glutamyl transpeptidase. The data indicate that serine-borate complex is a transition state inhibitor of gamma-glutamyl transpeptidase.

Azaserine↗
PubMed1981

Selective killing of human malignant cell lines deficient in methylthioadenosine phosphorylase, a purine metabolic enzyme.

Seven out of 31 (23%) human malignant tumor cell lines had no detectable methylthioadenosine phosphorylase activity (less than 0.001 nmol/min per mg of protein), assayed with 5'-chloroadenosine as substrate. The enzyme-deficient cell lines were derived from five leukemias, one melanoma, and one breast cancer. None of 16 cell lines of nonmalignant origin, derived from lymphocytes, fibroblasts, and epithelial cells, lacked the enzyme (range, 0.156-1.447 nmol/min per mg of protein). As detected by autoradiography, intact enzyme-positive cell lines normal immature bone marrow cells, and four specimens of malignant tumor cells incorporated the adenine moiety of 5'-chloroadenosine into nucleic acids; however, no enzyme-deficient cell lines used 5'-chloroadenosine. When both types of cell lines were cultured in a medium containing 0.4 microM methotrexate, 16 microM uridine, and 16 microM thymidine (or 10 microM azaserine alone), no cells grew. If methylthioadenosine was added to the same medium, only enzyme-positive cells increased in number; most enzyme-deficient cells were dead after 3 days. Thus, human malignant tumor cell lines naturally deficient in methylthioadenosine phosphorylase could be selectively killed when de novo purine synthesis was inhibited and methylthioadenosine was the only exogenous source of purines.

Adenosine↗
PubMed2001

Excessive hexosamines block the neuroprotective effect of insulin and induce apoptosis in retinal neurons.

In addition to microvascular abnormalities, neuronal apoptosis occurs early in diabetic retinopathy, but the mechanism is unknown. Insulin may act as a neurotrophic factor in the retina via the phosphoinositide 3-kinase/Akt pathway. Excessive glucose flux through the hexosamine biosynthetic pathway (HBP) is implicated in the development of insulin resistance in peripheral tissues and diabetic complications such as nephropathy. We tested whether increased glucose flux through the HBP perturbs insulin action and induces apoptosis in retinal neuronal cells. Exposure of R28 cells, a model of retinal neurons, to 20 mm glucose for 24 h attenuated the ability of 10 nm insulin to rescue them from serum deprivation-induced apoptosis and to phosphorylate Akt compared with 5 mm glucose. Glucosamine not only impaired the neuroprotective effect of insulin but also induced apoptosis in R28 cells in a dose-dependent fashion. UDP-N-acetylhexosamines (UDP-HexNAc), end products of the HBP, were increased approximately 2- and 15-fold after a 24-h incubation in 20 mm glucose and 1.5 mm glucosamine, respectively. Azaserine, a glutamine:fructose-6-phosphate amidotransferase inhibitor, reversed the effect of 20 mm glucose, but not that of 1.5 mm glucosamine, on attenuation of the ability of insulin to promote cell survival and phosphorylate Akt as well as accumulation of UDP-HexNAc. Glucosamine also impaired insulin receptor processing in a dose-dependent manner but did not decrease ATP content. By contrast, in L6 muscle cells, glucosamine impaired insulin receptor processing but did not induce apoptosis. These results suggest that the excessive glucose flux through the HBP may direct retinal neurons to undergo apoptosis in a bimodal fashion; i.e. via perturbation of the neuroprotective effect of insulin mediated by Akt and via induction of apoptosis possibly by altered glycosylation of proteins. The HBP may be involved in retinal neurodegeneration in diabetes.

Adenosine Triphosphate↗
PubMedDate not supplied

Multivariate statistical methods in toxicology. III. Specifying joint toxic interaction using multiple regression analysis.

Multiple regression is widely employed to study the contribution of components to the toxicologic effect of a mixture. Here, use is made of the fact that data obtained from standard curves of substances and from their mixtures are separable in regression analysis. Thus, under an assumption of additivity of responses, regression coefficients obtained for components in mixtures alone should be the same as for the individual substances. A t-test is developed such that nonsignificant t values support additivity, negative significant values support antagonism, and positive significant values support synergism. The results are applied to data on the mutagenicity of binary mixtures of azaserine, 4-nitroquinoline N-oxide, and 9-aminoacridine in TA 100 in the Ames assay.

4-Nitroquinoline-1-oxide↗
PubMed1991

Effects of castration, alone and in combination with aminoglutethimide, on growth of (pre)neoplastic lesions in exocrine pancreas of rats and hamsters.

We studied the effects of hormonal manipulation by orchiectomy, alone or in combination with the aromatase inhibitor aminoglutethimide (AGT), and by luteinizing hormone-releasing hormone agonist (LH-RH-A) (goserelin) treatment on the development of early putative (pre)neoplastic lesions induced in the pancreas of rats and hamsters by azaserine and N-nitrosobis(2-oxopropyl)amine respectively. Treatment of the animals started 1 week after the last injection with carcinogen and continued for 4 months. Orchiectomy caused a significant inhibition of growth of acidophilic atypical acinar cell nodules in the rat model, whereas surgical castration did not show an effect in the hamster model. In rats, but not in hamsters, orchiectomy resulted in a significant decrease in body weight and in absolute, but not relative pancreatic weight. Treatment of the animals with AGT or goserelin did not cause a significant effect on the development of either putative preneoplastic acinar lesions in rat pancreas or early ductular lesions in hamster pancreas. Hamsters showed clearly higher plasma epidermal growth factor (EGF) and insulin-like growth factor 1 (IGF-1) concentrations than rats, while plasma testosterone levels were significantly lower. Plasma EGF and IGF-1 levels decreased with increasing age in both control and treatment groups. Compared to controls there were no clear unequivocal effects of treatment on EGF, IGF-1 and gastrin levels. Plasma testosterone levels decreased by orchiectomy and LH-RH-A treatment. In rats hormone-induced effects on food intake and altered nutritional status might be important with respect to the development of carcinogen-induced preneoplastic pancreatic lesions.

Aminoglutethimide↗
PubMed1974

The locus for human adenine phosphoribosyltransferase on chromosome no. 16.

Evidence for assigning the locus determining the structure of adenine phosphoribosyltransferase (APRT) to human chromosome No. 16 is presented. Hybrids of APRT-deficient mouse cells and of human fibroblasts having normal APRT were isolated by fusing the parental cells with Sendai virus, blocking de novo purine nucleotide synthesis with azaserine and selecting for hybrids that could use exogenous adenine. The hybrid clones that were studied had only APRT activity that was indistinguishable from human APRT with regard to electrophoretic migration and reaction with antibodies against the partially purified human enzyme. No. 16 was the only human chromosome consistently present in all of the clones, and in one clone, it was the only human chromosome detected. Selection against hybrid cells with 2,6-diaminopurine (DAP) yielded DAP-resistant survivors that lacked chromosome No. 16. One hybrid that originally had an intact No. 16 yielded adenine-utilizing subclones that lacked No. 16 but had a new submetacentric chromosome. The distribution of centromere-associated heterochromatin and the fluorescence pattern indicated that this chromosome consisted of a mouse telocentric chromosome and the long arm of No. 16. Cells having the submetacentric chromosome had human APRT. Both the enzyme and the chromosome were absent in DAP-resistant derivatives. These results suggest that the structure of APRT is defined by a locus on the long arm of human chromosome No. 16.

Adenine↗
PubMed1996

Expression and characterization of gastrin-releasing peptide receptor in normal and cancerous pancreas.

The biochemical and pharmacological characteristics of specific binding sites for gastrin-releasing peptide (GRP) were investigated in normal exocrine pancreas and in an azaserine-induced pancreatic carcinoma in the rat, under similar experimental conditions. Cells from both types of tissues contained rapid, reversible, temperature-dependent, and highly specific binding sites for GRP. Scatchard analysis of equilibrium data obtained with normal and tumor plasma membranes indicated a single class of high-affinity sites (KD = 0.42 +/- 0.06 and 0.35 +/- 0.05 nM, respectively), but the number of GRP receptors was significantly different (Bmax = 31 +/- 4.5 and 189 +/- 20 fmol/mg protein, respectively). Binding of 125I-GRP1-27 was sensitive to GTP analogues, suggesting that the GRP receptor is functionally linked to a guanyl regulatory protein; however, the wheat germ agglutinin-agarose purified receptor had lost this G-protein activity. Cross-linking of 125I-GRP1-27 either to normal and neoplastic cells or to crude membranes, solubilized membrane proteins, and partially purified receptors revealed the presence of a specific MW 75-kDa polypeptide. N-Glycanase treatment reduced this apparent MW to about 45 kDa. Together, these data suggest that normal and tumor pancreatic cells contain a specific GRP receptor that is expressed more on malignant pancreatic tissues.

Animals↗
PubMed2002

Linkage between toxin production and purine biosynthesis in Clostridium difficile.

The production of toxins A and B by Clostridium difficile was greatly enhanced under biotin-limited conditions, in which a 140-kDa protein was expressed strongly. Gene cloning revealed that this protein was a homologue of formylglycinamidine ribonucleotide synthetase (FGAM synthetase, EC 6.3.5.3), which is known as PurL in Escherichia coli and catalyses the fourth step of the de novo purine biosynthesis pathway. This enzyme consisted of a single polypeptide, although FGAM synthetases of gram-positive bacteria usually consist of two subunits. Inhibition of the enzymic activity of C. difficile PurL by O-diazoacetyl-L-serine (azaserine) resulted in enhanced toxin B production even in biotin-sufficient conditions. In contrast, blockade of the preceding step of the PurL catalysing step by sulfamethoxazole inhibited toxin B production almost completely. These results suggest that accumulation of formylglycinamide ribonucleotide (FGAR), a substrate of FGAM synthetase, enhances toxin production by C difficile and depletion of FGAR reduces toxin production.

Amino Acid Sequence↗