Uptake of uric acid, xanthine and hypoxanthine by brush-border membrane vesicles from mouse small intestine

Using mouse small intestine brush-border membrane vesicles virtually free of xanthine oxidase (EC 1.2.3.2) and free of uricase (EC 1.7.3.3) the uptake of the purines uric acid, xanthine and hypoxanthine have been studied. The sodium-dependent overshoot phenomenon shown to exist for the uptake into the vesicles for d-glucose and l-phenylalanine was not observed with the purines. However, the uptake of the three purines in the presence of NaCl or KCl was greater than the uptake in the presence of either NaSCN or mannitol. Although 12.9% of the xanthine uptake and 17.6% of the hypoxanthine uptake was attributed to binding to the membranes, almost all the uric acid uptake was due to transport into an osmotically active space. The apparent intravesicular volume, calculated after 60 min incubation, for the three purines was consistently greater than the values obtained with d-glucose, l-phenylalanine equilibration, suggesting slow continuing penetration of purines associated with swelling or an apparent accumulation of purines within the vesicles associated with normal vesicle volume.     

Direct demonstration of the active salvage of preformed purines by murine tumors

The purine de novo biosynthetic pathway has become a target for chemotherapeutic agents and because of the possible contribution of the salvage of extracellular purines to cellular purine pools an examination of the ability of mouse tumors in vivo to exploit the salvage pathways was undertaken. Our data reveal that circulating radiolabeled preformed purines are rapidly and actively salvaged in both normal liver and in two different types of model tumors. The salvaged purines were found to be distributed between both acid soluble cytoplasmic purines and acid insoluble nucleic acid associated purine species. The ability to salvage adenine, the most abundant circulating purine in C57BL/6 mice, was highest in normal liver with the two different model tumors demonstrating lower specific activities of salvaged acid soluble purines. The amount of radiolabel incorporated into acid insoluble nucleic acid was dependent upon the tumor type. Because of the active salvage observed in these tumors, the mechanism by which de novo purine biosynthesis inhibitors serve as effective chemotherapeutic agents may be more complex than simple biosynthetic inhibition.     

Amino acid catalyzed condensation of purines and pyrimidines with 2-deoxyribose.

Mild heating of aqueous mixtures containing 2-deoxyribose, amino compounds, and purines or pyrimidines produces derivatives of the purines and pyrimidines in high yield. Among the major products formed are 2,3-dideoxy-3-(1'-pyrimidino)pentose and 2,3-dideoxy-3-(9'-purino)pentose. The mechanism of the reaction includes amine-catalzyed dehydration of the alpha, beta positions of the sugar followed by addition of the purine or pyrimidine to the double bond. Rapid addition of purines and pyrimidines to alpha, beta-unsaturated carbonyl compounds (such as acrolin) is a general phenomenon which does not require an amine catalyst. While multiple derivatization of the purines will take place, the N-9 derivative is formed first.     

Lactobacillus gasseri PA-3, but not L. gasseri OLL2996, reduces the absorption of purine nucleosides in rats

Lactobacillus gasseri PA-3 (PA-3) is a bacterial strain with a strong ability to degrade purine nucleosides. We previously showed that PA-3 incorporates purines in vitro and that oral administration of PA-3 and purines to rats attenuated their absorption of purines. It remains unclear whether these effects of PA-3 depend on bacterial strains. This study therefore compared the abilities of PA-3 and another bacterial strain of L. gasseri, OLL2996, which has shown decreased ability to degrade purine nucleosides in vitro, to incorporate purine nucleosides and to inhibit the absorption of purines fed to rats. Each bacterial strain was incubated in the presence of ¹⁴C-adenosine or ¹⁴C-inosine and the incorporation of each purine was evaluated by measuring their radioactivity. In vivo, rats were fed ¹⁴C-labeled purines along with PA-3 or OLL2996 and the absorption of these ¹⁴C-labeled purines was evaluated by analyzing radioactivity of blood samples. PA-3 incorporated about twice as much ¹⁴C-adenosine and ¹⁴C-inosine as OLL2996. The elevation of radioactivity levels in blood was 10–20% lower in rats treated with PA-3 than in control rats, after feeding with both ¹⁴C-adenosine and ¹⁴C-inosine as purines. In contrast, treatment with OLL2996 did not have statistically significant effects on radioactivity compared with the control group. These results indicate that the magnitude of bacterial inhibition of purine absorption is dependent on bacterial strain, correlating at least partly with the ability to incorporate and degrade purines.     

Purines inhibit poly(ADP-ribose) polymerase activation and modulate oxidant-induced cell death.

Purines such as adenosine, inosine, and hypoxanthine are known to have potent antiinflammatory effects. These effects generally are believed to be mediated by cell surface adenosine receptors. Here we provide evidence that purines protect against oxidant-induced cell injury by inhibiting the activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP). Upon binding to broken DNA, PARP cleaves NAD+ into nicotinamide and ADP-ribose and polymerizes the latter on nuclear acceptor proteins such as histones and PARP itself. Overactivation of PARP depletes cellular NAD+ and ATP stores and causes necrotic cell death. We have identified some purines (hypoxanthine, inosine, and adenosine) as potential endogenous PARP inhibitors. We have found that purines (hypoxanthine > inosine > adenosine) dose-dependently inhibited PARP activation in peroxynitrite-treated macrophages and also inhibited the activity of the purified PARP enzyme. Consistently with their PARP inhibitory effects, the purines also protected interferon gamma + endotoxin (IFN/LPS) -stimulated RAW macrophages from the inhibition of mitochondrial respiration and inhibited nitrite production from IFN/LPS-stimulated macrophages. We have selected hypoxanthine as the most potent cytoprotective agent and PARP inhibitor among the three purine compounds, and investigated the mechanism of its cytoprotective effect. We have found that hypoxanthine protects thymocytes from death induced by the cytotoxic oxidant peroxynitrite. In line with the PARP inhibitory effect of purines, hypoxanthine has prevented necrotic cell death while increasing caspase activity and DNA fragmentation. As previously shown with other PARP inhibitors, hypoxanthine acted proximal to mitochondrial alterations as hypoxanthine inhibited the peroxynitrite-induced mitochondrial depolarization and secondary superoxide production. Our data imply that purines may serve as endogenous PARP inhibitors. We propose that, by affecting PARP activation, purines may modulate the pattern of cell death during shock, inflammation, and reperfusion injury.     

Purine metabolism in Mycobacterium leprae grown in armadillo liver

Abstract Mycobacterium leprae organisms generally incorporated purines more rapidly than pyrimidines into nucleic acids from the incubation medium. Purine synthesis de novo took place at a very slow rate suggesting a preference of the organism for preformed purines. In cell-free extracts of leprosy bacilli, enzyme for scavenging and interconversion of purines were detected. The results are discussed in the light of the failure to cultivate M. leprae in vitro, and the use of labelled substrates to determine the viability of suspensions of leprosy bacilli and their sensitivity to anti-leprosy drugs.     

Use of Analogues and the Substrate-Sensitivity of Mutants in Analysis of Purine Uptake and Breakdown in Aspergillus nidulans

Aspergillus mutants resistant to various purine analogues (purine, 8-azaguanine, 2-thioxanthine, and 2-thiouric acid) are defective in at least one step of purine uptake or breakdown. The properties of these mutants show that there are two uptake systems for purines, one which mediates the uptake of hypoxanthine, guanine, and adenine, and the other, xanthine and uric acid. Allantoinase-less strains are sensitive to the toxic effects of allantoin accumulation. They are severely inhibited when grown in the presence of naturally occurring purines. Mutant strains derived from these, resistant to naturally occurring purines, may be isolated. These are either wild-type revertants, or carry a second metabolic block in the uptake or breakdown of purines. The properties of these double mutants confirm the interpretation of the nature of the analogue-resistant mutants.     

Evaluation of purine utilization by Lactobacillus gasseri strains with potential to decrease the absorption of food-derived purines in the human intestine

Abstract

It is well accepted that frequent and heavy intake of purine-rich foods causes elevation of serum uric acid levels, which is a risk factor of hyperuricemia. Reducing intestinal absorption of dietary purines may attenuate the elevation of serum uric acid levels and exacerbation of hyperuricemia. This reduction may be achieved by the ingestion of lactic acid bacteria that take up purines in the intestine. In this study, we investigated the degree of uptake and utilization of purines of three lactobacilli strains. Among them, Lactobacillus gasseri PA-3 (PA-3) showed the greatest incorporation of ¹⁴C-adenine. PA-3 also incorporated ¹⁴C-adenosine and ¹⁴C-AMP. Additionally, using defined growth medium, PA-3 demonstrated greater proliferation in the presence of these purines than in their absence. Although further investigation is required, ingestion of PA-3 may lower serum uric acid levels by reducing intestinal absorption of purines in humans.     

New (1‐Deaza)Purine Derivatives via Efficient C‐2 Nitration of the (1‐Deaza)Purine Ring

Nitration of substituted (1‐deaza)purines using a mixture of tetrabutylammonium nitrate (TBAN) and trifluoracetic acid anhydride (TFAA) was applied to prepare nitrosubstituted (1‐deaza)purines at low temperature. The nitro group influences the system twofold: 1) it activates other substituents towards nucleophilic aromatic substitution and 2) it can be substituted itself leading to a variety of di‐substituted (1‐deaza)purines, also via solid phase syntheses. Several of the molecules obtained were studied for their antiprotozoal activity and for interactions with the different human adenosine receptors.     

New (1-deaza)purine derivatives via efficient C-2 nitration of the (1-deaza)purine ring

Nitration of substituted (1-deaza)purines using a mixture of tetrabutylammonium nitrate (TBAN) and trifluoracetic acid anhydride (TFAA) was applied to prepare nitrosubstituted (1-deaza)purines at low temperature. The nitro group influences the system twofold: 1) it activates other substituents towards nucleophilic aromatic substitution and 2) it can be substituted itself leading to a variety of di-substituted (1-deaza)purines, also via solid phase syntheses. Several of the molecules obtained were studied for their antiprotozoal activity and for interactions with the different human adenosine receptors.     

Purine and pyrimidine contents of some desoxypentose nucleic acids

The distribution of purines and pyrimidines in desoxypentose nucleic acids prepared from a variety of animal and plant sources has been studied. 1. The nucleic acids were prepared from calf thymus, calf kidney, sheep spleen, horse spleen, chicken erythrocyte, turtle erythrocyte, trout sperm, shad testes, sea urchin sperm, wheat germ, and Pneumococcus Type III. 2. Separate hydrolyses were carried out for the determination of purines and pyrimidines. These procedures permitted nearly quantitative recovery of nucleic acid phosphorus in many of the preparations examined. 3. In the case of those preparations where a quantitative recovery was obtained it can be concluded that no bases other than adenine, guanine, thymine, and cytosine were present in appreciable amounts. 4. The distribution of purines and pyrimidines in all the nucleic acids studied renders the tetranucleotide hypothesis untenable. 5. The results of the analyses have indicated no great differences in the composition of these nucleic acids with respect to purines and pyrimidines.     

Kinetics of luminol sonochemiluminescence quenched by purines

A homogeneous chemiluminescence (CL) reaction was initiated by ultrasound irradiation. Luminol sonochemiluminescence (SCL) reaction kinetics were determined under pseudo‐first‐order conditions, and the reaction followed the model for simple rise–fall kinetics. In addition, SCL quenching reactions induced by purines were also investigated in which the interactions between luminol and purines were analysed using the Stern–Volmer (S‐V) mechanism. The results implied that the high rate constant of luminol CL quenched by purines may be attributed to ground state interactions originating from hydrogen bonding. Copyright © 2012 John Wiley & Sons, Ltd.     

Purine Uptake and Utilization by the Avian Malaria Parasite Plasmodium lophurae*

SYNOPSIS. Plasmodium lophurae cannot carry out extensive de novo purine biosynthesis, and depends upon the host erythrocyte for a supply of preformed purines. Exogenous purines taken up by the parasitized erythrocyte may constitute a major source of preformed purines for parasite nucleotide biosynthesis. The uptake of exogenous radioactive purine compounds and their incorporation into nucleic acids by duck erythrocytes parasitized with P. lophurae, uninfected erythrocytes, and erythrocyte-free parasites were studied. P. lophurae was found to have a remarkable ability, both intracellularly and extracellularly, to take up and utilize certain exogenous purines such as adenosine, inosine, and hypoxanthine. Incorporation studies indicated that this species has a functional purine salvage pathway by which inosine, hypoxanthine, and adenosine can be converted to both adenine and guanine nucleotides.     

Anomalously Coupled Nucleosides

Abstract

Polyphosphoric amide reagents are used to prepare purines which are coupled with unprotected 2-deoxy-D-ribose at C-3 of the carbohydrate using tributylammonium polyphosphates in chloroform. Phthalimide can be used instead of purines to produce N-protected 3-amino-2,3-dideoxypentoses.     

Cardiac outflow of amino acids and purines during myocardial ischemia and reperfusion.

A novel application of microdialysis was studied, in which myocardial outflow of amino acids and purines was monitored by intravasal microdialysis in the myocardial venous outflow during ischemia and reperfusion. Microdialysis catheters were introduced into the great cardiac vein, pulmonary artery, and external jugular vein in 20 anesthetized pigs. The left anterior descending artery was occluded in four groups of pigs for 0, 10, 15, and 60 min. Ischemia was followed by 120 min of reperfusion. Microdialysis samples were analyzed for taurine, aspartate, glutamate, hypoxanthine, inosine, and guanosine. Myocardial infarction developed when ischemia exceeded 10 min. Taurine, aspartate, inosine, and guanosine increased early in the great cardiac vein during ischemia. We found the outflow patterns of amino acids and purines to be graded in response to different lengths of ischemia. In this study we have demonstrated a graded outflow of amino acids and purines in response to ischemia and a positive correlation between infarct size and myocardial outflow of amino acids and purines. This could be of value in a clinical setting to quantify the extent of myocardial damage.     

Conformational transitions of flanking purines in HIV-1 RNA dimerization initiation site kissing complexes studied by CHARMM explicit solvent molecular dynamics

Dimerization of HIV-1 genomic RNA is initiated by kissing loop interactions at the Dimerization Initiation Site (DIS). Dynamics of purines that flank the 5' ends of the loop-loop helix in HIV-1 DIS kissing complex were explored using explicit solvent molecular dynamics (MD) simulations with the CHARMM force field. Multiple MD simulations (200 ns in total) of X-ray structures for HIV-1 DIS Subtypes A, B, and F revealed conformational variability of flanking purines. In particular, the flanking purines, which in the starting X-ray structures are bulged-out and stack in pairs, formed a consecutive stack of four bulged-out adenines at the beginning of several simulations. This conformation is seen in the crystal structure of DIS Subtype F with no interference from crystal packing, and was frequently reported in our preceding MD studies performed with the AMBER force field. However, as CHARMM simulations progressed, the four continuously stacked adenines showed conformational transitions from the bulged-out into the bulged-in geometries. Although such an arrangement has not been seen in any X-ray structure, it has been suggested by a recent NMR investigation. In CHARMM simulations, in the longer time scale, the flanking purines display the tendency to move to bulged-in conformations. This is in contrast with the AMBER simulations, which indicate a modest prevalence for bulged-out flanking base positions in line with the X-ray data. The simulations also suggest that the intermolecular stacking between purines from the opposite hairpins can additionally stabilize the kissing complex.     

Evidence for Frameshift Mutations in the Hish Gene of Escherichia Coli Causing Synthesis of a Partially Active Glutamine Amidotransferase

Among eight strains carrying acridine-induced mutations in hisH, five which mapped at four different sites in the promoter-distal region of the gene showed His+ phenotypes on media containing a purine. By complementation analysis, hisH enzyme was shown to be required for growth on purines. Purine-sensitive His+ revertants of strains able to grow on purines carried second-site mutations which in one case could be shown to map in hisG. Strains able to grow on purines were able to grow on 2-thiazolyl-DL-alanine, too. We conclude that frameshift mutations in the promoter-distal part of the hisH gene of E. coli do not completely abolish the activity of the gene product.     

Prokaryotes that grow optimally in acid have purine-poor codons in long open reading frames

In nucleic acids the N-glycosyl bonds between purines and their ribose sugar moities are broken under acid conditions. If one strand of a duplex DNA segment were more vulnerable to mutation than the other, then the archaeon Picrophilus torridus, with an optimum growth pH near zero, could have adapted by decreasing the purine content of that strand. Yet, P. torridus has an optimum growth temperature near 60°C, and thermophiles prefer purine-rich codons. We found that, as in other thermophiles, high growth temperature correlates with the use of purine-rich codons. The extra purines are often in third, non-amino acid determining, codon positions. However, as in other acidophiles, as open reading frame lengths increase, there is increased use of purine-poor codons, particularly those without purines in second, amino acid-determining, codon positions. Thus, P. torridus can be seen as adapting (a) to temperature by increasing its purines in all open reading frames without greatly impacting protein amino acid compositions, and (b) to pH by decreasing purines in longer open reading frames, thereby potentially impacting protein amino acid compositions. It is proposed that longer open reading frames, being larger mutational targets, have become less vulnerable to depurination by virtue of pyrimidine for purine substitutions.     

Potentiation by purines of the growth-inhibitory effects of sulphonamides on Escherichia coli K12 and the location of the gene which mediates this effect

The increased toxicity of sulphonamides for Escherichia coli in the presence of low concentrations (50-100 microM) of purines or purine nucleosides has been confirmed and investigated further. The potentiating effect of a purine was dependent upon the activity of the appropriate phosphoribosyl transferase: a gpt mutant strain was not potentiated by guanine but remained fully sensitive to the addition of adenine. Mutants resistant to the potentiating effect of all purines have been isolated and partially characterized. The site of these mutations has been located in the region between oriC and asnA at minute 83 on the E. coli chromosome map. It is suggested that this locus be temporarily designated psp (potentiation of sulphonamides by purines) because these mutants have unaltered sensitivities to sulphonamides acting alone. Mutations in PurA, purR and folB did not affect the potentiation of sulphonamides by purines. Hypoxanthine-insensitive strains harbouring lambda asn20 were as sensitive as the wild-type to the potentiating effect. This result suggests that these lysogens are heterozygous for psp and that the wild-type allele is dominant. It is probable that psp is a regulatory gene, affecting some rate-limiting step in the biosynthesis of methionine.     

Biosynthesis and scavenging of purines by pathogenic mycobacteria including Mycobacterium leprae

Purine biosynthesis de novo could not be detected in suspensions of Mycobacterium leprae isolated from armadillo tissue. In contrast, non-growing suspensions of other pathogenic mycobacteria, also isolated from infected host tissue did synthesize purines. Rates of synthesis, judged by incorporation of [2-14C]glycine or [3-14C]serine into nucleic acid purines were 600 times higher in M. microti and 110 times higher in M. avium--both isolated from infected mouse tissue--than the lowest possible rate detectable and therefore the highest possible rate in M. leprae. The rate of purine synthesis relative to purine scavenging (judged by comparing incorporation of [3-14C]serine and [8-14C]hypoxanthine into nucleic acid purines in suspensions of mycobacteria) varied only slightly--4-fold in M. microti and 6-fold in M. avium--whether organisms were harvested from media with or without purines, from media with a low nitrogen content but containing a purine, from mice or even with starved organisms. Thus, the failure of M. leprae to synthesize purines could not be explained as either a result of using non-growing mycobacteria in the incubations with 14C-labelled precursors or as repression or inhibition of synthesis de novo. It appears that M. leprae requires a supply of the purine ring from its environment. Nucleotides, which may be the major source of the purine ring in the intracellular environment, were not taken up directly by M. leprae but could be hydrolysed first to nucleosides and then taken up.