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Adenine nucleotide turnover in hypoxanthine-guanine phosphoribosyl-transferase deficiency: evidence for an increased contribution of purine biosynthesis de novo.

This study examined whether increased purine biosynthesis de novo in HGPRT deficiency contributes to adenine nucleotide formation compared with normal subjects. Four HGPRT deficient patients and four normal subjects received intravenously 10 to 25 microCi of [8-14C]adenine to radiolabel the adenine nucleotide pool followed five days later by a rapid infusion of fructose to stimulate purine nucleotide degradation. Fructose infusion increased urinary radioactivity in the enzyme-deficient patients to 141% +/- 13% (mean +/- SEM) of the baseline values compared with 1,067% +/- 102% in normal subjects (P less than .01). The absolute mean increase in total urinary purines in the patients was 17.96 +/- 3.36 and 10.38 +/- 3.80 mmol/g creatinine in controls (P less than .05). The apparent specific radioactivity of urinary purines increased in the control group from a mean of 1.29 X 10(5) to 3.64 X 10(5) cpm/mmol of purines (P less than .02) but decreased in the enzyme-deficient subjects from a mean of 1.66 X 10(5) to 1.38 X 10(5) cpm/mmol. To assess if the decrease in the specific activity of urinary purines was due to an elevated rate of de novo purine synthesis, two HGPRT-deficient patients were treated with allopurinol and adenine followed five days later by a fructose infusion. The administration of adenine increased the specific activity of urinary purines after the infusion of fructose from a mean baseline value of 1.05 X 10(5) to 1.42 X 10(5) cpm/mmol of purines.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenine↗

Biochemical basis of the prevention of 6-thiopurine toxicity by the nucleobases, hypoxanthine and adenine.

Co-incubation of human leukemia cell lines with naturally occurring nucleobases (hypoxanthine or adenine) significantly prevented the cytotoxic activity of 6-thiopurines. Extracellular hypoxanthine decreased the transport of 6-mercaptopurine into cells, but adenine had no significant effect. However, intracellular thioinosine monophosphate accumulation in the presence of 10 microM, 6-mercaptopurine was reduced to below 1% or 10% of that of the controls when 50 microM hypoxanthine or adenine was added, respectively. Finally, in adenine phosphoribosyl transferase deficient mutants, adenine provided no protective effect against 6-thiopurines, whereas hypoxanthine retained its modulating activity. These data suggest that the nucleobases compete with 6-thiopurines for the ribose-phosphate donor, 5'-phosphoribosyl-1-pyrophosphate, thus preventing the formation of active metabolites of 6-thiopurines.

2-Aminopurine↗

In vitro adenine nucleotide catabolism in African catfish spermatozoa.

It has been shown recently that African catfish (Clarias gariepinus) spermatozoa possess relatively low ATP content and low adenylate energy charge (AEC). One of the possible explanations for this phenomenon is that the spermatozoa actively catabolize adenine nucleotides. A relatively high rate of such catabolism could then contribute to the low ATP concentration and low adenylate energy charge observed in the spermatozoa in vitro. To check this hypothesis, we investigated ATP content and adenine nucleotide catabolism in African catfish spermatozoa stored at 4 degrees C in the presence of glycine as an energetic substrate. Our results indicate that the storage of African catfish sperm at 4 degrees C in the presence of glycine causes time-dependent ATP depletion. In contrast to ATP, the AMP content increases significantly during the same period of sperm storage, while the ADP increases only slightly. Moreover, a significant increase of inosine and hypoxanthine content was also found. Hypoxanthine was accumulated in the storage medium, but xanthine was found neither in spermatozoa nor in the storage medium. It indicates that hypoxanthine is not converted to xanthine, probably due to lack of xanthine oxidase activity in catfish spermatozoa. Present results suggest that adenine nucleotides may be converted to hypoxanthine according to the following pathway: ATP-->ADP-->AMP (adenosine/IMP)-->inosine-->hypoxanthine. Moreover, hypoxanthine seems to be the end product of adenine nucleotide catabolism in African catfish spermatozoa. In conclusion, our results suggest that a relatively high rate of adenine nucleotide catabolism contributes to the low ATP concentration and low adenylate energy charge observed in African catfish spermatozoa in vitro.

Adenine↗

Complete deficiency of adenine phosphoribosyltransferase. Report of a family.

We studied the clinical and biochemical manifestations of complete adenine phosphoribosyltransferase deficiency in the kindred of a male homozygous child excreting stones of 2,8-dihydroxyade-nine. Abnormal amounts of adenine, 8-hydroxyade-nine and 2,8-dihydroxyadenine (25 per cent of total purine metabolites) appeared in the urine of the propositus and his clinically normal brother, but not in heterozygotes or a control. Adenine phosphoribosyl-transferase activity in erythrocytes was less than 1 per cent of normal in both homozygotes and varied from 20 to 57 per cent of normal in six heterozygotes. Heterozygotes exhibited neither hyperuricemia nor gout. Treatment of the propositus with allopurinol and a low purine diet stopped stone formation. In addition, excretion of 2,8-dihydroxyadenine decreased. An autosomal recessive mode of inheritance with variable expression in the phenotype is indicated. Homozygotes may be detected by their raised urinary adenine levels or absence of detectable erythrocyte adenine phosphoribosyltransferase activity (or both).

Adenine↗

The adenine phosphoribosyltransferase from Giardia lamblia has a unique reaction mechanism and unusual substrate binding properties.

Purine phosphoribosyltransferases catalyze the Mg2+ -dependent reaction that transforms a purine base into its corresponding nucleotide. They are present in a wide variety of organisms including plants, mammals, and parasitic protozoa. Giardia lamblia, the causative agent of giardiasis, lacks de novo purine biosynthesis and relies primarily on adenine and guanine phosphoribosyltransferases (APRTase and GPRTase) constituting two independent and essential purine salvage pathways. The APRTase from G. lamblia was cloned and expressed with a 6-His tag at its C terminus and purified to apparent homogeneity. Adenine and alpha-d-5-phosphoribosyl-1-pyrophosphate (PRPP) have K(m) values of 4.2 and 143 microm with a k(cat) of 2.8 s(-1) in the forward reaction, whereas AMP and PP(i) have K(m) values of 87 and 450 microm with a k(cat) of 9.5 x 10(-3) s(-1) in the reverse reaction. Product inhibition studies indicated that the forward reaction follows a random Bi Bi mechanism. Results from the kinetics of equilibrium isotope exchange further verified a random Bi Bi mechanism in the forward reaction. In a mutant enzyme, F25W, with kinetic constants similar to those of the wild type and a tryptophan residue at the adenine binding site, the addition of adenine or AMP to the free mutant enzyme resulted in fluorescence quenching, whereas PRPP caused fluorescence enhancement. The dissociation constants thus estimated are 16.5 microm for adenine, 14.3 microm for AMP, and 83.0 microm for PRPP. PP(i) exerted no detectable effect on the tryptophan fluorescence at all, suggesting a lack of PP(i) binding to the free enzyme. An ordered substrate binding in the reverse reaction with AMP bound first followed by PP(i) is thus postulated.

Adenine↗

Configuration of a scintillation proximity assay for the activity assessment of recombinant human adenine phosphoribosyltransferase.

Adenine phosphoribosyltransferase plays a role in purine salvage by catalyzing the direct conversion of adenine to adenosine monophosphate. The involvement of the purine salvage pathway in tumor proliferation and angiogenesis makes adenine phosphoribosyltransferase a potential target for oncology drug discovery. We have expressed and characterized recombinant, N-terminally His-tagged human adenine phosphoribosyltransferase. Two assay formats were assessed for use in a high throughput screen: a spectrophotometric-based enzyme-coupled assay system and a radiometric ionic capture scintillation proximity bead assay format. Ultimately, the scintillation proximity assay format was chosen because of automated screening compatibility limitations of the coupled assay. We describe here the biochemical characterization of adenine phosphoribosyltransferase and the development of a robust, homogeneous, 384-well assay suitable for high throughput screening.

Adenine↗

Study of the role of puring phosphoribosyltransferases in the uptake of adenine and guanine by Schizosaccharomyces pombe cells.

1. In the yeast Schizosaccharomyces pombe 972h-, the uptake rate of both adenine and guanine is related to variations in the specific activity of the corresponding phosphoribosyltransferases during the growth of the culture. Furthermore, the mutant strains dap 1, devoid of adenine phosphoribosyltransferase activity, and pur 1, devoid of guanine phosphoribosyltransferase activity have a lowered uptake rate of adenine and guanine respectively, along with an increased apparent Km value for these purines in comparison to the wild-type 972h. 2. The uptake rate of the purines is strongly dependent on the pH of the uptake medium in 972h- as well as in the strains dap 1 and pur 1, the optimum being between pH4 and pH5. 3. A new method of extraction of 5-phosphoribosyl-1-pyrophosphate from the yeast has been devised. Important fluctuations of the P-Rib-P2 pool were measured in S. pombe at different stages of growth, the maximum taking place at the start of the exponential phase, whereas no variations in the specific activity of the P-Rib-P2 synthetase could be observed during the growth. The P-Rib-P2 intracellular content in the mutants devoid of purine phosphoribosyltransferases, namely pur 1, dap 1 and pur 1, dap 1, was increased up to 5-fold as compared to the wild-type strain. 4. The effect of intracellular concentrations of P-Rib-P2, a substrate for phosphoribosyltransferases, on the uptake rate of purines has been studied: addition of formycin to the growth medium lowered simultaneously the P-Rib-P2 intracellular content and the uptake of adenine and guanine. 5. Although our results demonstrate the activating effect of phosphoribosyltransferase activities on the uptake of adenine and guanine, they do not support the hypothesis of a 'group translocation' mechanism.

Adenine↗

ENHANCEMENT BY ADENINE OF THE INHIBITION OF SALMONELLA TYPHIMURIUM BY ETHIONINE.

Smith, Robert C. (Auburn University, Auburn. Ala.), and W. D. Salmon. Enhancement by adenine of the inhibition of Salmonella typhimurium by ethionine. J. Bacteriol. 89:1494-1498. 1965.-The inhibition by ethionine of the growth of Salmonella typhimurium was increased by adenine and several other purines. This effect was counteracted by the addition of methionine to the cultures. There was no preferential inhibition of nucleic acid or protein synthesis by adenine plus ethionine. Adenine stimulated the uptake of radioactive ethionine by the cells. Adenine may produce the effects observed by increasing the rate at which ethionine enters the cell and reaches its primary site of antibacterial action.

Adenine↗

Lineage-associated differences in adenine methylation patterns of mammalian-associated Campylobacter fetus isolates: a possible role for epigenetic factors in host tropism and pathogenesis.

Mammalian Campylobacter fetus (CF) is divided into two subspecies, C. fetus fetus (CFF) and C. fetus venerealis (CFV), the latter being bovine-adapted and responsible for the notifiable disease bovine genital campylobacteriosis (BGC). Differentiation between CF subspecies has traditionally been undertaken by a few biochemical tests, but these are complicated by the existence of a biotype, C. fetus venerealis intermedius (CFVi), which shares attributes of both CFF and CFV. Molecular methods targeting specific genes have gained acceptance for more accurate subtype identification and align well with whole-genome analysis. However, limited genomic diversity between subtypes has confounded efforts to understand the genetic basis for differential host tropism and pathogenesis of these organisms. A previous study of a small cohort of C. fetus isolates suggested that dam gene coding variations might correlate with CF subtype. Accordingly, this study examines a cohort of 331 C. fetus genomes, representative of all seven phylogenetic groups for their complement of adenine methylases and the genomic motifs they target in representative isolates. All CF isolates retained a cfeM1 gene, the presence of which correlates with RAATTY methylation, while seven other adenine methylase genes exhibited distinct cladal distributions. Notably, a cjeM1 gene appears to target the CCAN7TAG/CTAN7TGG motif in CFV and CFVi isolates only. Given the increasing recognition of the impact of adenine methylation on bacterial-host interactions, further exploration of the role of adenine methylation in C. fetus pathogenesis could reveal mechanisms contributing to BGC and thus aid in its eradication.IMPORTANCECampylobacter fetus remains an important zoonotic pathogen, for which a better understanding of its host tropism and pathogenesis is sought. However, the limited genomic variation observed between subtypes has to date confounded efforts in this regard. This study suggests that an alternative approach that examines epigenetic differences between subtypes, specifically adenine methylation patterns, may reveal mechanisms critical to the pathologies of these organisms.

Animals↗

Inhibitory action of the adenine analog, 4-aminopyrazolo(3,4-d)pyrimidine, in Crithidia fasciculata.

The adenine analog 4-aminopyrazolo(3,4-d)pyrimidine inhibits the growth of the kinetoplastid (trypanosomatid) flagellate Crithidia fasciculata. This inhibition is partially overcome only by adenine (of a number of purines tested), with an inhibition index of 0.025. More effective reversal of inhibition is obtained with any of a number of naturally occurring pyrimidine compounds, up to a concentration of 0.18 mM. Higher concentrations of pyrimidines or addition of guanine, as well as adenine and uracil, to the medium increases inhibition. The analog (presumably as the ribonucleotide) was found not to be inhibitory to any enzyme of the pyrimidine biosynthetic pathway that could be tested. It is suggested that the analog competes with adenine for adenine phosphoribosyltransferase (AMP:pyrophosphate phosphoribosyltransferase, EC 2.4.2.7), is converted to a ribonucleotide, and is incorporated into nucleic acid.

Adenine↗

Nucleotide precursors modify the effects of isoproterenol. Studies on heart function and cardiac adenine nucleotide content in intact rats.

In closed-chest rats, isoproterenol (ISO, 25 mg/kg), 5 hours after subcutaneous administration, increased heart rate by 53%, left ventricular (LV) dP/dtmax by 80%, and cardiac output by 37%. LV systolic pressure (LVSP, -10%), mean arterial pressure (MAP, -12%), and total peripheral resistance (TPR, -36%) were diminished. In separate experiments, continuous intravenous infusion of adenine (50 mg/kg/hr) for 5 hours reduced heart rate (-11%), LVSP (-16%), MAP (-20%), TPR (-33%), and LV dP/dtmax (-20%). Cardiac output was increased (+20%). Inosine has been shown to have similar effects, except for a decline in cardiac output. Adenine (50 mg/kg/hr) attenuated the ISO-induced increase in heart rate and LV dP/dtmax and aggravated the decline in LVSP, MAP, and TPR. The increase in cardiac output was not changed. Inosine (200 mg/kg/hr) modified the ISO effects to a similar extent. Ribose (200 mg/kg/hr) added to the adenine infusion did not have functional effects. However, it aggravated the modifying influence of inosine on LVSP, LV dP/dtmax, and MAP. ISO reduced the cardiac ATP content (mumol/g) from a control value of 5.02 +/- 0.06 (n = 12) to 3.51 +/- 0.13 (n = 10). Adenine (3.56 +/- 0.21, n = 7) and ribose (3.64 +/- 0.11, n = 9) alone did not affect it, but inosine attenuated it (4.33 +/- 0.08, n = 8). Adenine and inosine in combination with ribose abolished the ISO-induced ATP decline (5.18 +/- 0.23, n = 7, and 4.76 +/- 0.10, n = 8, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Adenine↗

[Microassay of adenine by an enzymatic isotope dilution kinetics method].

Owing to the very low levels of adenine in the intracellular and extracellular compartments and its low excretion by the kidney, no method of estimation was, until now, sufficiently specific and sensitive to determine precisely quantities of the order of 1 nanomole. The method of "isotopic enzymatic kinetic dilution" proposed by Newsholme et Taylor, has been used. The kinetic conditions of the reaction catalysed by adenine-phosphoribosyltransferase are favourable, [in particular KM (adenine) is very low, about 2.1(-6) M] and are not very sensitive to the action of other effectors. The technique proposed permits one to determine quantities of adenine between 0.05 and 1.2 nmole, i.e. 0.007 to 0.16 mug, with a precision of about 5 p. cent. Easy to carry out, it is useful in large series. Normal values in man of adenine thus measured (15 adult subjects) were as follows: Plasma: 1.13 +/- 0.41 nmoles.ml(-1), i.e. 0.152 +/-0 0.055 mug.ml(-1). Red cells: 3.65 +/- 0.87 nmoles.ml(-1), i.e. 0.493 +/- 0.117 mug.ml(-1). Urine (24 hour excretion): 11.41 +/- 1.24 mumoles, i.e. 1.54 +/- 0.17 mg.

Adenine↗

Effects of inosine and adenine on nucleotide levels in the post-ischemic rat heart, perfused with and without pyruvate.

Reports on enhanced nucleotide regeneration by purines during reperfusion are conflicting. We have, therefore, evaluated the effects of inosine or adenine, administered after ischemia, on adenine nucleotide levels and function in isolated rat hearts. The hearts were perfused with a Tyrode solution, containing 10 mM D-glucose, with or without 5 mM pyruvate. After 15 minutes without flow, the hearts were reperfused for 45 minutes with 20 microM purine and 0.5 mM D-ribose. Adenine nucleotide levels tended to recover better in the purine-treated groups. The purines decreased the ATP/ADP ratio by 10-15% (p less than 0.05) if pyruvate was absent. The IMP level in the inosine/glucose group exceeded that in all other groups by a factor of two (p less than 0.001). Inosine increased the adenosine concentration in the effluent sixfold (p less than 0.005). The hypoxanthine concentration rose up to four times following adenine treatment (p less than 0.05). The administration of purine, with or without pyruvate, did not affect mechanical recovery, heart rate or coronary flow. We conclude that inosine and adenine failed to improve cardiac function and hardly affected nucleotide levels in the reperfused heart.

Adenine↗

[Mutations of resistance to 2,6-diaminopurine and 6-methylpurine that affect adenine phosphoribosyltransferase in Escherichia coli K-12].

Independently obtained mutations (apt) of resistance to DAP (2,6-diaminopurine) and MP (6-methylpurine), that affect adenine phosphoribosyltransferase (APRT) in Escherichia coli, are different in their effect on the conversion of several substrates of APRT, such as DAP, MP, MAP (6-methylaminopurine) and adenine, to their nucleotide derivatives. Most of mutants were resistant to DAP and MP, unable to utilize MAP (as purine source) and differed in their ability to uptake adenine from the medium. Among the mutants capable to utilize adenine the following types are found: (1) resistant to DAP and MP, but capable of utilizing MAP, and (2) resistant to DAP, capable of utilizing MAP, but sensitive to MP. The gene apt encoding APRT is located between genes proC and purE; the frequency of cotransduction between proC and several apt mutations is found to be 1.7--2% and purE-apt--to be 5--10.8%. Mutations apt block up the ability of purine-dependent (pur) bacteria lacking purine nucleoside phosphorylase (pup) to use purine ribonucleosides as purine sources. The degree of that blocking depends on the ability of apt mutants to convert adenine to AMP via APRT. These observations confirm our previous data, that the ability of pur pup mutants to use purine ribonucleosides depends on the activity of APRT.

2-Aminopurine↗

Raman spectroscopy study of acid-base and structural properties of 9-[2-(phosphonomethoxy)ethyl]adenine in aqueous solutions.

The acid-base properties of the acyclic antiviral nucleotide analogue 9- [2-(phosphonomethoxy)ethyl] adenine (PMEA) in aqueous solutions are studied by means of Raman spectroscopy in a pH range of 1-11 and compared with the properties of its common adenosine monophosphate counterparts (5'-AMP, 3'-AMP, and 2'-AMP). Factor analysis is used to separate the spectra of pure ionic species (PMEA2-, HPMEA-, H2PMEA, H3PMEA+) in order to determine their abundance, sites of protonation, and corresponding spectroscopic pK(a) values. The characteristic Raman features of the neutral adenine moiety in PMEA2- and HPMEA- species resemble those of neutral adenine in the AMPs, whereas significant differences are observed between the Raman spectra of the N1-protonated adenine of the solute zwitterionic H2PMEA and its N1-protonated AMP counterparts. On the contrary, the spectrum of crystalline H2PMEA, adopting an "anti-like" conformation, is found to be similar to the N1-protonated AMPs in solution. To explain peculiar Raman features a "syn-like" conformation is suggested for N1-protonated PMEA species in aqueous solutions instead of an anti-like one adopted by H2PMEA in crystals or by common AMPs in aqueous solutions. A physical mechanism of the anti-like to syn-like conformational transition of the solute PMEA that is due to adenine protonation and the flexibility of the (phosphonomethoxy)ethyl group is proposed and discussed.

Acids↗

Induction of polyploidy in human lymphocytes in vitro by excess adenine, but not by adenosine.

It is known that high levels of DNA precursors can be both clastogenic and mutagenic in cultured cell lines and in vivo. The purpose of the present study was to examine at an observational level the cytogenetic effects of adenine and adenosine in primary human cell cultures. Human peripheral blood lymphocytes from four donors were cultured and treated with a range of concentrations of adenine and adenosine. Although no increase in sister chromatid exchange (SCE) frequency was observed with either compound, there was a statistically significant, dose-related increase in the proportion of polyploid cells in cultures treated with adenine, but not in those treated with adenosine. Some of the polyploid metaphases found after adenine treatment contained diplochromosomes, suggesting that endoreduplication might have been involved in polyploid formation in these cells. It is concluded that a high level of adenine can cause genetic changes in human lymphocytes by interfering with mitosis, perhaps by disturbing the balance of DNA precursor pools.

Adenine↗

The metabolism of adenine derivatives in different parts of the brain of the rat, and their release from hypothalamic preparations on excitation.

Five enzymes concerned with the metabolism of adenine derivatives were assayed in seven regions of the rat brain. A region which included the hypothalamus had the highest AMP deaminase and adenosine deaminase activities, while its 5'-nucleotidase activities were relatively low. The enzymes named and also the uptake of [14C]adenine by incubated tissue samples were more active with hypothalamic than with neocortical tissues. On superfusion with glucose-bicarbonate saline after assimilating [14C]adenine, the hypothalamic tissues released about 0.2 per cent of their 14C content per minute. This release was increased fourfold with electrical excitation but the presence of 0.25 muM tetrodotoxin prevented most of this increase. The compounds released during superfusion and electrical stimulation were preponderantly hypoxanthine, inosine, and adenosine, with only small amounts of adenine nucleotides. The output of all these compounds increased during the period of stimulation and also the proportion of adenine nucleotides increased when stimulation was carried out in the presence of tetrodotoxin. The output of the nucleotides and adenosine increased more promptly when stimulated than did that of the other compounds named. The results are discussed in terms of the metabolic roles of the enzymes concerned. and in relation to whether the enzymes are acting on intracellular or extracellular substrates.

AMP Deaminase↗

Adenine nucleotide metabolism and contractile dysfunction in heart failure--biochemical aspects, animal experiments, and human studies.

In myocardial hypertrophy and heart failure a series of adaptational changes occur some multiplying contractile units, others slowing shortening velocity and increasing economy of contraction. The demonstration of energy-saving mechanisms in heart failure has prompted further investigations of energy providing and utilizing metabolic pathways. The use of myocardial ATP as a substrate occurs mainly at the myosin-ATPase and at the Ca-ATPase of the sarcoplasmic reticulum. As the Michaelis constant of both enzymes for ATP is in the micromolar (microM) range, whereas cellular ATP content is about 5000 microM, these enzymes are not controlled by the availability of ATP as a substrate. In experimental heart failure in large animals, normal or reduced creatine phosphate levels (in most cases together with normal adenine nucleotides) have been described. Reduced creatine phosphate is found in models with increased oxygen consumption, and creatine phosphate may buffer the ATP pool in these models. In human heart failure due to dilated cardiomyopathy, where resting oxygen consumption per unit mass and lactate extraction are normal in most patients, normal adenine nucleotides, creatine phosphate, and mitochondrial function have been described in the initial studies. These results have been challenged by one study showing decreased ATP levels in dilated cardiomyopathy, correlating with the decrease in ejection fraction. However, only ATP has been measured in this study, whereas total adenine nucleotides may be a more suitable parameter. Recently published results have again demonstrated normal ATP and total adenine nucleotides in human heart failure. In the same patients, significantly decreased myocardial norepinephrine was measured, indicating that metabolic changes had occurred in these hearts, but were independent of adenine nucleotides.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗