Induction and repression of enzymes involved in exogenous purine compound utilization of Bacillus cereus

5'-Nucleotidase, adenosine phosphorylase, adenosine deaminase and purine nucleoside phosphorylase, four enzymes involved in the utilization of exogenous compounds in Bacillus cereus, were measured in extracts of this organism grown in different conditions. It was found that adenosine deaminase is inducible by addition of adenine derivatives to the growth medium, and purine, nucleoside phosphorylase by metabolizable purine and pyrimidine ribonucleosides. Adenosine deaminase is repressed by inosine, while both enzymes are repressed by glucose. Evidence is presented that during growth of B. cereus in the presence of AMP, the concerted action of 5'-nucleotidase and adenosine phosphorylase, two constitutive enzymes, leads to formation of adenine, and thereby to induction of adenosine deaminase. The ionsine formed would then cause induction of the purine nucleoside phosphorylase and repression of the deaminase. Taken together with our previous findings showing that purine nucleoside phosphorylase of B. cereus acts as a translocase of the ribose moiety of inosine inside the cell (Mura, U., Sgarrella, F. and Ipata, P.L. (1978) J. Biol Chem. 253, 7905-7909), our results provide a clear picture of the molecular events leading to the utilization of the sugar moiety of exogenous AMP, adenosine and inosine as an energy source.     

Phosphorylase-mediated mobilization of the amino group of adenine in Bacillus cereus

Mobilization of the ribose moiety of purine nucleosides as well as of the amino group of adenine may be realized in Bacillus cereus by the concerted action of three enzymes: adenosine phosphorylase, adenosine deaminase, and purine nucleoside phosphorylase. In this pathway, ribose-1-phosphate and inorganic phosphate act catalytically, being continuously regenerated by purine nucleoside phosphorylase and adenosine phosphorylase, respectively. As a result of such a metabolic pathway, adenine is quantitatively converted into hypoxanthine, thus overcoming the lack of adenase in B. cereus.     

Metabolism of Exogenous Purine Bases and Nucleosides by Salmonella typhimurium

Purine-requiring mutants of Salmonella typhimurium LT2 containing additional mutations in either adenosine deaminase or purine nucleoside phosphorylase have been constructed. From studies of the ability of these mutants to utilize different purine compounds as the sole source of purines, the following conclusions may be drawn. (i) S. typhimurium does not contain physiologically significant amounts of adenine deaminase and adenosine kinase activities. (ii) The presence of inosine and guanosine kinase activities in vivo was established, although the former activity appears to be of minor significance for inosine metabolism. (iii) The utilization of exogenous purine deoxyribonucleosides is entirely dependent on a functional purine nucleoside phosphorylase. (iv) The pathway by which exogenous adenine is converted to guanine nucleotides in the presence of histidine requires a functional purine nucleoside phosphorylase. Evidence is presented that this pathway involves the conversion of adenine to adenosine, followed by deamination to inosine and subsequent phosphorolysis to hypoxanthine. Hypoxanthine is then converted to inosine monophosphate by inosine monophosphate pyrophosphorylase. The rate-limiting step in this pathway is the synthesis of adenosine from adenine due to lack of endogenous ribose-l-phosphate.     

Profiles of purine biosynthesis, salvage and degradation in disks of potato (Solanum tuberosum L.) tubers

To find general metabolic profiles of purine ribo- and deoxyribonucleotides in potato (Solanum tuberosum L.) plants, we looked at the in situ metabolic fate of various ¹⁴C-labelled precursors in disks from growing potato tubers. The activities of key enzymes in potato tuber extracts were also studied. Of the precursors for the intermediates in de novo purine biosynthesis, [¹⁴C]formate, [2-¹⁴C]glycine and [2-¹⁴C]5-aminoimidazole-4-carboxyamide ribonucleoside were metabolised to purine nucleotides and were incorporated into nucleic acids. The rates of uptake of purine ribo- and deoxyribonucleosides by the disks were in the following order: deoxyadenosine > adenosine > adenine > guanine > guanosine > deoxyguanosine > inosine > hypoxanthine > xanthine > xanthosine. The purine ribonucleosides, adenosine and guanosine, were salvaged exclusively to nucleotides, by adenosine kinase (EC 2.7.1.20) and inosine/guanosine kinase (EC 2.7.1.73) and non-specific nucleoside phosphotransferase (EC 2.7.1.77). Inosine was also salvaged by inosine/guanosine kinase, but to a lesser extent. In contrast, no xanthosine was salvaged. Deoxyadenosine and deoxyguanosine, was efficiently salvaged by deoxyadenosine kinase (EC 2.7.1.76) and deoxyguanosine kinase (EC 2.7.1.113) and/or non-specific nucleoside phosphotransferase (EC 2.7.1.77). Of the purine bases, adenine, guanine and hypoxanthine but not xanthine were salvaged for nucleotide synthesis. Since purine nucleoside phosphorylase (EC 2.4.2.1) activity was not detected, adenine phosphoribosyltransferase (EC 2.4.2.7) and hypoxanthine/guanine phosphoribosyltransferase (EC 2.4.2.8) seem to play the major role in salvage of adenine, guanine and hypoxanthine. Xanthine was catabolised by the oxidative purine degradation pathway via allantoin. Activity of the purine-metabolising enzymes observed in other organisms, such as purine nucleoside phosphorylase (EC 2.4.2.1), xanthine phosphoribosyltransferase (EC 2.4.2.22), adenine deaminase (EC 3.5.4.2), adenosine deaminase (EC 3.5.4.4) and guanine deaminase (EC 3.5.4.3), were not detected in potato tuber extracts. These results suggest that the major catabolic pathways of adenine and guanine nucleotides are AMP → IMP → inosine → hypoxanthine → xanthine and GMP → guanosine → xanthosine → xanthine pathways, respectively. Catabolites before xanthosine and xanthine can be utilised in salvage pathways for nucleotide biosynthesis.     

Genetic and physiological characterization of the purine salvage pathway in the archaebacterium Methanobacterium thermoautotrophicum Marburg.

The enzymes involved in the purine interconversion pathway of wild-type and purine analog-resistant strains of Methanobacterium thermoautotrophicum Marburg were assayed by radiometric and spectrophotometric methods. Wild-type cells incorporated labeled adenine, guanine, and hypoxanthine, whereas mutant strains varied in their ability to incorporate these bases. Adenine, guanine, hypoxanthine, and xanthine were activated by phosphoribosyltransferase activities present in wild-type cell extracts. Some mutant strains simultaneously lost the ability to convert both guanine and hypoxanthine to the respective nucleotide, suggesting that the same enzyme activates both bases. Adenosine, guanosine, and inosine phosphorylase activities were detected for the conversion of base to nucleoside. Adenine deaminase activity was detected at low levels. Guanine deaminase activity was not detected. Nucleoside kinase activities for the conversion of adenosine, guanosine, and inosine to the respective nucleotides were detected by a new assay. The nucleotide-interconverting enzymes AMP deaminase, succinyl-AMP synthetase, succinyl-AMP lyase, IMP dehydrogenase, and GMP synthetase were present in extracts; GMP reductase was not detected. The results indicate that this autotrophic methanogen has a complex system for the utilization of exogenous purines.     

Purine uptake and release in rat C6 glioma cells: nucleoside transport and purine metabolism under ATP-depleting conditions

Adenosine, through activation of membrane-bound receptors, has been reported to have neuroprotective properties during strokes or seizures. The role of astrocytes in regulating brain interstitial adenosine levels has not been clearly defined. We have determined the nucleoside transporters present in rat C6 glioma cells. RT-PCR analysis, (3)H-nucleoside uptake experiments, and [(3)H]nitrobenzylthioinosine ([(3)H]NBMPR) binding assays indicated that the primary functional nucleoside transporter in C6 cells was rENT2, an equilibrative nucleoside transporter (ENT) that is relatively insensitive to inhibition by NBMPR. [(3)H]Formycin B, a poorly metabolized nucleoside analogue, was used to investigate nucleoside release processes, and rENT2 transporters mediated [(3)H]formycin B release from these cells. Adenosine release was investigated by first loading cells with [(3)H]adenine to label adenine nucleotide pools. Tritium release was initiated by inhibiting glycolytic and oxidative ATP generation and thus depleting ATP levels. Our results indicate that during ATP-depleting conditions, AMP catabolism progressed via the reactions AMP --> IMP --> inosine --> hypoxanthine, which accounted for >90% of the evoked tritium release. It was surprising that adenosine was not released during ATP-depleting conditions unless AMP deaminase and adenosine deaminase were inhibited. Inosine release was enhanced by inhibition of purine nucleoside phosphorylase; ENT2 transporters mediated the release of adenosine or inosine. However, inhibition of AMP deaminase/adenosine deaminase or purine nucleoside phosphorylase during ATP depletion produced release of adenosine or inosine, respectively, via the rENT2 transporter. This indicates that C6 glioma cells possess primarily rENT2 nucleoside transporters that function in adenosine uptake but that intracellular metabolism prevents the release of adenosine from these cells even during ATP-depleting conditions.     

Purine catabolism in rat brain (author's transl)

In soluble rat brain fraction, the specific activities of purine nucleoside phosphorylase, guanine deaminase, 5'Nucleotidase and adenosine deaminase, decrease in their mentioned order. A kinetic parameter comparison between these enzymes shows that 5'Nucleotidase with AMP has the lowest KM and the greatest Vmax values, while purine nucleoside phosphorylase has its lowest KM and its greatest Vmax values with guanosine and with inosine, respectively. The enzymes activity is not modified by the metabolic intermediates differently from their own reaction products which behave as competitive inhibitors.     

Pathways of adenine nucleotide catabolism in primary rat muscle cultures

The pathways of AMP degradation and the metabolic fate of adenosine were studied in cultured myotubes under physiological conditions and during artificially induced enhanced degradation of ATP. The metabolic pathways were gauged by tracing the flow of radioactivity from ATP, prelabelled by incubation of the cultures with [¹⁴C]adenine, into the various purine derivatives. The fractional flow from AMP to inosine through adenosine was estimated by the use of the adenosine deaminase (EC 3.5.4.4) inhibitors, coformycin and 2′-deoxycoformycin. The activities of the enzymes involved with AMP and adenosine metabolism were determined flow of label from ATP to diffusible bases and nucleosides, most of which are effluxed to the incubation medium. This catabolic flow is mediated almost exclusively by the activity of AMP deaminase (EC 3.5.4.6), rather than by AMP 5′-nucleotidase (EC 3.1.3.5), reflecting the markedly higher V_max/K_m ratio for the deaminase. Enhancement of ATP degradation by inhibition of glycolysis or by combined inhibition of glycolysis and of electron transport resulted in a markedly greater flux of label from adenine nucleotides to nucleosides and bases, but did not alter significantly the ratio between AMP deamination and AMP dephosphorylation, which remained around 19:1. Combined inhibition of glycolysis and of electron transport resulted, in addition, in accumulation of label in IMP, reaching about 20% of total AMP degraded. In the intact myotubes at low adenosine concentration, the anabolic activity of adenosine kinase was at least 4.9-fold the catabolic activity of adenosine deaminase, in accord with the markedly higher V_max/K_m ratio of the kinase for adenosine. The results indicate the operation in the myotube cultures, under various rates of ATP degradation, of the AMP to IMP limb of the purine nucleotide cycle. On the other hand, the formation of purine bases and nucleosides, representing the majority of degraded ATP, indicates inefficient activity of the IMP to AMP limb of the cycle, as well as inefficient salvage of hypoxanthine under these conditions.     

Enzymatic activities for interconversion of purines in spirochetes.

Enzymatic activities that catalyze the interconversion of purines and purine derivatives were detected in cell extracts of Spirochaeta aurantia, Spirochaeta stenostrepta, Treponema succinifaciens, and Treponema denticola. Phosphoribosyltransferase activities present in cell extracts of each of the four spirochete species functioned in the conversion of adenine, hypoxanthine, and guanine to AMP, IMP, and GMP, respectively. Nucleotidase activities in the extracts mediated the formation of nucleosides from nucleotides. The conversion of adenosine, inosine, and guanosine to the respective purine bases was catalyzed by nucleoside phosphorylase and, in some instances, by nucleoside hydrolase activities. Guanine deaminase activity was found in both S. aurantia and S. stenostrepta, whereas adenosine deaminase activity was detected only in S. aurantia. Adenine deaminase activity in T. succinifaciens extracts was sensitive to O2 and was relatively resistant to heating. Our results indicate that the four species of spirochetes studied possess a broad spectrum of purine interconversion enzymes. It is suggested that these enzymes may function in metabolic processes important for the survival of spirochetes in nutrient-poor natural environments.     

Utilization of 2,6-diaminopurine by Salmonella typhimurium

The pathway for the utilization of 2,6-diaminopurine (DAP) as an exogenous purine source in Salmonella typhimurium was examined. In strains able to use DAP as a purine source, mutant derivatives lacking either purine nucleoside phosphorylase or adenosine deaminase activity lost the ability to do so. The implied pathway of DAP utilization was via its conversion to DAP ribonucleoside by purine nucleoside phosphorylase, followed by deamination to guanosine by adenosine deaminase. Guanosine can then enter the established purine salvage pathways. In the course of defining this pathway, purine auxotrophs able to utilize DAP as sole purine source were isolated and partially characterized. These mutants fell into several classes, including (i) strains that only required an exogenous source of guanine nucleotides (e.g., guaA and guaB strains); (ii) strains that had a purF genetic lesion (i.e., were defective in alpha-5-phosphoribosyl 1-pyrophosphate amidotransferase activity); and (iii) strains that had constitutive levels of purine nucleoside phosphorylase. Selection among purine auxotrophs blocked in the de novo synthesis of inosine 5'-monophosphate, for efficient growth on DAP as sole source of purine nucleotides, readily yielded mutants which were defective in the regulation of their deoxyribonucleoside-catabolizing enzymes (e.g., deoR mutants).     

Characterization of a cell culture model for the study of adenosine deaminase- and purine nucleoside phosphorylase-deficient immunologic disease.

The absence of erythrocytic adenosine deaminase (ADA) or purine nucleoside phosphorylase (PNP) has been associated with severe immunodeficiency disease in children. We have developed a cell culture model to study the possible relationships between purine salvage enzymes and immunologic function using an established T cell lymphosarcoma (S49) and a potent inhibitor of ADA, erythro-9(2-hydroxy-3-nonyl) adenine (EHNA). Wild-type S49 cells are killed by dexamethasone or dbc AMP, and adenosine (5 muM) in the presence of an ADA inhibitor (6 muM EHNA) also prevents the growth of and kills these S49 cells. It has been proposed that adenosine is toxic to lymphoid cells by virtue of its ability to increase the intracellular concentrations of cyclic AMP. We examined the sensitivity of three mutants of S49 cells, with distinctive defects in some component of cyclic AMP metabolism or action, to killing by adenosine and EHNA. All three mutants are resistant to killing by isoproterenol or cholera toxin and two are resistant to dbc AMP itself, but all are sensitive to killing by adenosine and EHNA. Similarly, two dexamethasone-resistant S49 mutants are as sensitive to adenosine and EHNA as are the wildtype cells. We have also simulated the purine nucleoside phosphorylase deficiency in S49 cells by adding inosine and adenosine to the growth medium. In the presence of EHNA or inosine, the toxic effects of adenosine can be partially reversed by addition of (10-20 muM) uridine, an observation suggesting that adenosine is toxic as the result of its inducing pyrimidine starvation.     

Mutants of Escherichia coli Defective in Ribonucleoside and Deoxyribonucleoside Catabolism

From Escherichia coli B, mutants were prepared that lacked the enzymes adenosine deaminase, cytidine deaminase, and purine nucleoside phosphorylase. In each case, the mutant lacked enzyme activity for both ribonucleoside and deoxyribonucleoside. Mutants lacking purine nucleoside phosphorylase lost the capacity to cleave the nucleosides of adenine, guanine, and hypoxanthine.     

Activity of purine enzyme metabolism in rat thymocytes after irradiation and after administration of riboxine

It has been established, that the total X-ray irradiation of animals takes influence upon the functional activity of key enzymes of adenine nucleotides metabolism: adenylatekinase, AMP deaminase, 5'-nucleotidase, adenosine deaminase and purine nucleoside phosphorylase in rat's thymocytes. The increase of activity of the investigated enzymes is observed in our experiment, except 5'-nucleotidase, which activity is authentically decreasing after irradiation (1.0 and 7.78 Gy). The injection of the preparation riboxine to experimental animals 15 min prior to the exposure has normalized the purine exchange enzymes activity.     

Genetic control of Escherichia coli K-12 strains' assimilation of 2,6-diaminopurine as a purine source]

Mutations of the resistance to 2,6-diaminopurine (apt), which affect adenine phosphoribosyltransferase, fail to permit the growth of Escherichia coli pur mutants (purine auxotrophs which cannot make inosine monophosphate de novo) on the medium with 2,6-diaminopurine (DAP) as the sole source of purines. Addition of a small amount of hypoxantine, but not guanine, stimulated the growth of mutants of pur apt and pur apt+ genotypes on the medium with DAP. The utilization of DAP as purine source in the presence of hypoxantine is blocked by mutations guaC (guanosine monophosphate reductase), add (adenosine deaminase) and pup (purine necleoside phosphorylase), suggesting that DAP are utilized via purine nucleoside phosphorylase and adenosine deaminase. The drm mutation (that increases the level of pentose-1-phosphate in the cell) does not activate the utilization of DAP. The results indicate that a step, that limits the utilization of DAP as the sole source of purines by pur mutants of E. coli, is the deamination of DAP nucleoside.     

Investigation of various genotype characteristics for inosine accumulation in Escherichia coli W3110

For the derivation of an inosine-overproducing strain from the wild type microorganism, it is known that the addition of an adenine requirement, removal of purine nucleoside hydrolyzing activity, removal of the feedback inhibition, and repression of key enzymes in the purine nucleotides biosynthetic pathway are essential. Thus, the disruption of purA (adenine requirement), deoD (removal of purine nucleosides phosphorylase activity), purR (derepression of the regulation of purine nucleotides biosynthetic pathway), and the insensitivity of the feedback inhibition of phosphoribosylpyrophosphate (PRPP) amidotransferase by adenosine 5'-monophosphate (AMP) and guanosine 5'-monophosphate (GMP) were done in the Escherichia coli strain W3110, and then the inosine productivity was estimated. In the case of using a plasmid harboring the PRPP amidotransferase gene (purF) that encoded a desensitized PRPP amidotransferase, purF disrupted mutants were used as the host strains. It was found that the innovation of the four genotypes brought about a small amount of inosine accumulation. Furthermore, an adenine auxotrophic mutant of E. coli showed inappropriate adenine use because its growth could not respond efficiently to the concentration of adenine added. As the presence of adenosine deaminase is well known in E. coli and it is thought to be involved in adenine use, a mutant disrupted adenosine deaminase gene (add) was constructed and tested. The mutant, which is deficient in purF, purA, deoD, purR, and add genes, and harboring the desensitized purF as a plasmid, accumulated about 1 g of inosine per liter. Although we investigated the effects of purR disruption and purF gene improvement, unexpectedly an increase in the inosine productivity could not be found with this mutant.     

Pentatrichomonas hominis: purine salvage pathway

1. Pentatrichomonas hominis was found incapable of de novo synthesis of purines. 2. Pentatrichomonas hominis can salvage adenine, guanine, hypoxanthine, adenosine, guanosine and inosine, but not xanthine for the synthesis of nucleotides. 3. HPLC tracing of radiolabelled purines or purine nucleosides revealed that adenine, adenosine and hypoxanthine are incorporated into adenine nucleotides and IMP through a similar channel while guanine and guanosine are salvaged into guanine nucleotides via another route. There appears to be no direct interconversion between adenine and guanine nucleotides. Interconversion between AMP and IMP was observed. 4. Assays of purine salvage enzymes revealed that P. hominis possess adenosine kinase; adenosine, guanosine and inosine phosphotransferases; adenosine, guanosine and inosine phosphorylases and AMP deaminase.     

Utilization of exogenous purine compounds in Bacillus cereus. Translocation of the ribose moiety of inosine.

Intact cells of Bacillus cereus catalyze the breakdown of exogenous AMP to hypoxanthine and ribose 1-phosphate through the successive action of 5'-nucleotidase, adenosine deaminase, and inosine phosphorylase. Inosine hydrolase was not detectable, even in crude extracts. Inosine phosphorylase causes a "translocation" of the ribose moiety (as ribose 1-phosphate) inside the cell, while hypoxanthine remains external. Even though the equilibrium of the phosphorolytic reaction favors nucleoside synthesis, exogenous inosine (as well as adenosine and AMP) is almost quantitatively transformed into external hypoxanthine, since ribose 1-phosphate is readily metabolized inside the cell. Most likely, the translocated ribose 1-phosphate enters the sugar phosphate shunt, via its prior conversion into ribose 5-phosphate, thus supplying the energy required for the subsequent uptake of hypoxanthine in B. cereus.     

Purine metabolism in microplasmodia of Physarum polycephalum.

The uptake and utilization of purine nucleosides and purines in microplasmodia of Physarum polycephalum were investigated. The results revealed a unique pattern, namely that exogenous purine nucleosides are readily taken up and metabolised, while free purine bases are hardly taken up. The pathways of incorporation have been elucidated in studies with whole cells and with cell-free extracts. The ribonucleosides (adenosine, inosine and guanosine) can be converted into ribonucleotides in two ways; either directly catalysed by a kinase or by a phosphorolytic cleavage to the free base (adenine, hypoxanthine and guanine respectively) which can then be activated by a purine phosphoribosyltransferase. Apparently the purine phosphoribosyltransferases do not react with exogenous purine bases. The deoxyribonucleosides (deoxyadenosine, deoxyinosine and deoxyguanosine) are also phosphorolysed by purine nucleoside phosphorylase to adenine, hypoxanthine and guanine respectively. A portion of deoxyadenosine is directly phosphorylated to dAMP. It appears that only a minor part of the soluble nucleotide pool can be synthesised from exogenous supplied nucleosides and that none of the deoxyribonucleosides specifically label DNA. There is no catabolism of the purine moiety. In agreement with the above findings, we have found that analoguees of purine nucleosides are more toxic than their corresponding purine base analogues.     

Catabolic pathways of purine ribonucleotides and deoxyribonucleotides in lymphocytes

Deficiency of either one of the subsequent purine catabolic enzymes adenosine deaminase or purine nucleoside phosphorylase results in immunodeficiency disease in humans. However, the mechanism by which impairment of purine metabolism may cause immunodeficiency is unclear. In the present work we have studied the catabolism of purine ribonucleotides and deoxyribonucleotides in T lymphocytes to better understand the role of purine nucleoside phosphorylase and adenosine deaminase in the immune function. It was found that purine deoxyribonucleotides are degraded via catabolic pathways distinctly different from those used for purine ribonucleotide degradation. Thus both adenine and guanine ribonucleotides are deaminated to IMP whereas purine deoxyribonucleotides are exclusively dephosphorylated to the corresponding deoxyribonucleosides. These findings may explain the relatively higher degradation rates of purine deoxyribonucleotides in mammalian cells as compared to purine ribonucleotides. The catabolism of purine nucleotides is tightly linked to the active purine nucleoside cycles which consist of the phosphorolysis of purine nucleosides and deoxyribonucleosides to their corresponding bases, their salvage to monophosphates and back to the corresponding ribonucleosides. The above observations also imply that a possible role of the purine nucleoside cycles is to convert purine deoxyribonucleotides into their corresponding ribonucleotide derivatives. Deficiencies of purine nucleoside phosphorylase or of adenosine deaminase activities, enzymes which participate or lead to the purine nucleoside cycles, thus result in a selective impaired deoxyribonucleotide catabolism and immunodeficiency.     

Soluble Ecto-5′-nucleotidase (5′-NT), Alkaline Phosphatase,and Adenosine Deaminase (ADA1) Activities in Neonatal Blood Favor Elevated Extracellular Adenosine

Extracellular adenosine, a key regulator of physiology and immune cell function that is found at elevated levels in neonatal blood, is generated by phosphohydrolysis of adenine nucleotides released from cells and catabolized by deamination to inosine. Generation of adenosine monophosphate (AMP) in blood is driven by cell-associated enzymes, whereas conversion of AMP to adenosine is largely mediated by soluble enzymes. The identities of the enzymes responsible for these activities in whole blood of neonates have been defined in this study and contrasted to adult blood. We demonstrate that soluble 5′-nucleotidase (5′-NT) and alkaline phosphatase (AP) mediate conversion of AMP to adenosine, whereas soluble adenosine deaminase (ADA) catabolizes adenosine to inosine. Newborn blood plasma demonstrates substantially higher adenosine-generating 5′-NT and AP activity and lower adenosine-metabolizing ADA activity than adult plasma. In addition to a role in soluble purine metabolism, abundant AP expressed on the surface of circulating neonatal neutrophils is the dominant AMPase on these cells. Plasma samples from infant observational cohorts reveal a relative plasma ADA deficiency at birth, followed by a gradual maturation of plasma ADA through infancy. The robust adenosine-generating capacity of neonates appears functionally relevant because supplementation with AMP inhibited whereas selective pharmacologic inhibition of 5′-NT enhanced Toll-like receptor-mediated TNF-α production in neonatal whole blood. Overall, we have characterized previously unrecognized age-dependent expression patterns of plasma purine-metabolizing enzymes that result in elevated plasma concentrations of anti-inflammatory adenosine in newborns. Targeted manipulation of purine-metabolizing enzymes may benefit this vulnerable population.