Basis for the control of purine biosynthesis by purine ribonucleotides.

An animal model was used to determine the basis for the increase in purine biosynthesis that results from hepatic depletion of purine nucleotides, such as seen in patients with type I glycogen storage disease or following fructose administration. Mice were injected intravenously with glucose or fructose, 2.5 mg/g of body weight, and the animals were killed at 0, 3, and 30 min following carbohydrate infusion. Fructose, but not glucose, administration led to a threefold increase in [14C]glycine incorporation into hepatic purine nucleotides documenting an increase in the rate of purine biosynthesis in the liver of fructose-treated animals. In the fructose, but not the glucose-treated animals, there was a reduction in the hepatic content of purine nucleotides that are inhibitory for amidophosphoribosyltransferase, the enzyme that catalyzes the first reaction unique to the pathway of purine biosynthesis. PP-ribose-P, an important metabolite in the control of purine biosynthesis, was increased 2,3-fold in liver following fructose, but not glucose administration. In conjunction with the decrease in inhibitory nucleotides and increase in PP-ribose-P 29% of amidophosphoribosyltransferase was shifted from the large inactive to the small active form of the enzyme. Results of these studies demonstrate that the end-products of the pathway, purine nucleotides, control the activity of the enzyme that catalyzes the first reaction leading to purine nucleotide synthesis either through a direct effect of purine nucleotides on the enzyme, through an indirect effect of the change in nucleotides on PP-ribose-P synthesis, or a combination of these effects. The resultant changes in amidophosphoribosyltransferase conformation and activity provide a basis for understanding the increase in purine biosynthesis that results from hepatic depletion of purine nucleotides.     

Purine salvage networks in Giardia lamblia

Purine metabolism in Giardia lamblia was investigated by monitoring incorporation of radiolabeled precursors into purine nucleotides in the log-phase trophozoites cultivated in vitro in axenic media and incubated in buffered saline glucose. The lack of incorporation of formate, glycine, hypoxanthine, inosine, and xanthine into the nucleotide pool suggests the absence of de novo purine nucleotide synthesis and the inability to form IMP as the precursor of AMP and GMP in G. lamblia. Only adenine, adenosine, guanine, and guanosine were incorporated. Further analysis of the labeled nucleotides by HPLC indicated that adenine and adenosine are converted only to adenine nucleotides whereas guanine and guanosine are only incorporated into guanine nucleotides. There is no competition of incorporation between adenine/adenosine and guanine/guanosine, and there is no interconversion between adenine and guanine nucleotides. Results from analyzing [5'-3H]guanosine incorporation indicate that the ribose moiety is not incorporated with the guanine base. Assays of purine salvage enzymic activities in the crude extracts of G. lamblia revealed the presence of only four major enzymes; adenosine and guanosine hydrolases and adenine and guanine phosphoribosyl transferases. Apparently, G. lamblia has an exceedingly simple purine salvage system; it converts adenosine and guanosine to corresponding purine bases and then forms AMP and GMP by the actions of corresponding purine phosphoribosyl transferases. The guanine phosphoribosyl transferase in G. lamblia is interesting because it does not recognize either hypoxanthine or xanthine as substrate. It thus must have a unique substrate specificity and may be regarded as a potential target to attack as a rational approach to chemotherapeutic control of giardiasis.     

Analysis of purine nucleotides in muscle tissue by HPLC

Optimal conditions for simultaneous analysis of the purine nucleotides adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP), inosine monophosphate (IMP), inosine, adenosine, hypoxanthine, xanthine and uric acid in muscle samples by high-performance liquid chromatography (HPLC) were evaluated. A neutralized perchloric acid extract of freeze-dried human or rat skeletal muscle tissue was injected on to a reversed-phase silica column and eluted by a gradient composed of ammonium dihydrogen phosphate buffer and methanol. Good resolution for all the nucleotides was achieved within a retention time of about 20 min. Linearity for each of the nucleotides within the concentration intervals obtained in the samples was demonstrated. Purity of each peak was verified by use of the photodiode array technique. Reproducibility for biological samples with variation coefficients below 3.6% for ATP, ADP, AMP, inosine and hypoxanthine and 6.7% for IMP was obtained. The stability of the compounds after extraction was specifically addressed. Storing of frozen extracts at -20 degrees C for 24 h gave acceptable values, while storage for 7 days cannot be recommended. Storage of unfrozen extracts at 4 degrees C was acceptable for (up to) 7 h. This technique provides a sensitive, convenient and reliable method for simultaneous analysis of a large number of purine nucleotides in small skeletal muscle biopsies, provided that certain precautions are taken with respect to the instability of these metabolites.     

Purine metabolism of the human erythrocyte

Purine metabolism has been much investigated in human erythrocytes, both for the interest focused on this peculiar cell biochemistry, and four purine pathological implications in man. Most mammalian red blood cells lack de novo purine synthesis, and are completely dependent on base salvage pathway for their purine nucleotide requirement. Besides, human erythrocyte is devoid of some purine interconversion enzymes, thus becoming dependent on external supply of bases and nucleosides, particularly the adenylic ones. Red blood cell purine metabolism is very active, owing to its great need for nucleotides, and seems to aim greatly at the preservation of synthesized nucleotides against catabolic events. Available data on purine enzyme kinetic parameters and regulation, substrate and product cellular concentration and uptake are reviewed.     

Analysis of purine nucleotides in muscle tissue by HPLC

Optimal conditions for simultaneous analysis of the purine nucleotides adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP), inosine monophosphate (IMP), inosine, adenosine, hypoxanthine, xanthine and uric acid in muscle samples by high-performance liquid chromatography (HPLC) were evaluated. A neutralized perchloric acid extract of freeze-dried human or rat skeletal muscle tissue was injected on to a reversed-phase silica column and eluted by a gradient composed of ammonium dihydrogen phosphate buffer and methanol. Good resolution for all the nucleotides was achieved within a retention time of about 20 min. Linearity for each of the nucleotides within the concentration intervals obtained in the samples was demonstrated. Purity of each peak was verified by use of the photo-diode array technique. Reproducibility for biological samples with variation coefficients below 3.6% for ATP, ADP, AMP, inosine and hypoxanthine and 6.7% for IMP was obtained.

The stability of the compounds after extraction was specifically addressed. Storing of frozen extracts at –20^oC for 24 h gave acceptable values, while storage for 7 days cannot be recommended. Storage of unfrozen extracts at 4 ^oC was acceptable for (up to) 7 h.

This technique provides a sensitive, convenient and reliable method for simultaneous analysis of a large number of purine nucleotides in small skeletal muscle biopsies, provided that certain precautions are taken with respect to the instability of these metabolites.     

Anion-exchange high performance liquid chromatography method for the quantitation of nucleotides in human blood cells

An anion-exchange high performance liquid chromatography (HPLC) method is described for the quantitation of intracellular purine and pyrimidine nucleotides. With an ammonium phosphate salt and pH gradient, complete separation is achieved of all major nucleotides and several interfering substances, such as dehydroascorbic acid and NAD. For optimal resolution of the monophosphates, strict control of the equilibration pH is essential. To prevent interference by a degradation product of NADPH with the determination of GDP, the pH of the high-ionic strength buffer has to be in the range of 4.9-5.0. The use of radially compressed, prepacked cartridges filled with Partisil-10 SAX appeared to be a fast and cheap alternative for expensive stainless-steel columns. The use of ammonium phosphate buffers, in combination with precolumns filled with pellicular silica and SAX resin, and interim EDTA washes prevents baseline shift. This allows analysis at 0.01 Absorbance Units Full Scale during the entire column lifetime (about 180 analyses), which is sufficiently sensitive for the quantitation of low levels of nucleotides, especially when the amount of sample is limited.The usefulness of the presented Chromatographie system is demonstrated by the quantitation of the nucleotides in extracts of lymphocytes and neutrophils from the blood of healthy human donors. With this method nucleotide concentrations were measured, with a within-assay variation of 5–10% and an inter-donor variation of 10%.     

De novo synthesis of purine nucleotides in human peripheral blood leukocytes. Excessive activity of the pathway in hypoxanthine-guanine phosphoribosyltransferase deficiency.

Human peripheral blood leukocytes were studied for the presence and the regulatory properties of the pathway of de novo synthesis of purine nucleotides. The cells were found to incorporate the labeled precursors formate and glycine into purines. The rate of [14C]-formate incorporation was decreased by several compounds known to inhibit purine synthesis by affecting the activity by glutamine phosphoribosylpyrophosphate (PRPP) amidotransferase, the first committed enzyme in the pathway, either through decreasing the availability of PRPP, a substrate for this enzyme, or through exerting inhibition on this enzyme. PRPP availability in the leukocyte was found to be limiting for purine synthesis. Increased PRPP availability resulting from activation of PRPP synthetase by increasing inorganic phosphate (Pi) concentration caused acceleration of purine synthesis. On the other hand, no clear-cut evidence was obtained for the availability of ribose-5-phosphate in the leukocyte being rate limiting at physiological extracellular Pi concentration for PRPP generation, and thus for purine synthesis. However, the addition of methylene blue, which accelerates the oxidative pentose shunt that produces ribose-5-phosphate, resulted in acceleration of PRPP generation and of purine synthesis only when PRPP synthetase was largely activated at high Pi concentration. These results may be taken to suggest that ribose-5-phosphate availability is indeed not limiting for PRPP generation under physiological conditions. Purine synthesis de novo was accelerated more than 13-fold in the leukocytes of two gouty patients affected with partial deficiency of hypoxanthine-guanine phosphoribosyltransferase, but was normal in the leukocytes of an obligate heterozygote for this enzyme abnormality. The results domonstrate in peripheral human leukocytes the presence of the complete pathway of de novo synthesis of purine nucleotides and the manifestation in these cells of the biochemical consequences of hypoxanthine-guanine phosphoribosyltransferase deficiency, i.e., increased availability of PRPP and acceleration of purine synthesis de novo. The results indicate the usefulness of leukocytes as a model tissue for the study of purine metabolism in man.     

Erythrocyte nucleotide pattern in two children in a Norwegian family with pyrimidine 5'-nucleotidase deficiency

In the erythrocytes from two Norwegian children, a brother and a sister, with a hemolytic anemia due to pyrimidine 5'-nucleotidase deficiency, the pyrimidine and purine nucleotides have been investigated using HPLC with a strong anionic exchanger. The standard procedure was complemented with some additional elution systems which made it feasible to separate in the extract and to analyse, in addition to the conventional mono-, di- and triphosphates, UDP-glucose, UDP-N-acetylglucosamine, CDP-choline and CDP-ethanolamine. The two different purine nucleotides (A, G) and the two different pyrimidine nucleotides (U, C) exhibited normal ratios (energy charge ratios) between the conventional nucleotides. This would indicate that the erythrocytes have a sufficient energy production. It is suggested that the partly intravascular hemolysis might be due to disturbed synthesis of phospholipids.     

Potential chemotherapeutic targets in the purine metabolism of parasites

Parasites are responsible for a wide variety of infectious diseases in human as well as in domestic and wild animals, causing an enormous health and economical blight. Current containment strategies are not entirely successful and parasitic infections are on the rise. In the absence of availability of antiparasitic vaccines, chemotherapy remains the mainstay for the treatment of most parasitic diseases. However, there is an urgent need for new drugs to prevent or combat some major parasitic infections because of lack of a single effective approach for controlling the parasites (e.g., trypanosomiasis) or because some serious parasitic infections developed resistance to presently available drugs (e.g., malaria). The rational design of a drug is usually based on biochemical and physiological differences between pathogens and host. Some of the most striking differences between parasites and their mammalian host are found in purine metabolism. Purine nucleotides can be synthesized by the de novo and/or the so-called "salvage" pathways. Unlike their mammalian host, most parasites studied lack the pathways for de novo purine biosynthesis and rely on the salvage pathways to meet their purine demands. Moreover, because of the great phylogenic separation between the host and the parasite, there are in some cases sufficient distinctions between corresponding enzymes of the purine salvage from the host and the parasite that can be exploited to design specific inhibitors or "subversive substrates" for the parasitic enzymes. Furthermore, the specificities of purine transport, the first step in purine salvage, diverge significantly between parasites and their mammalian host. This review highlights the unique transporters and enzymes responsible for the salvage of purines in parasites that could constitute excellent potential targets for the design of safe and effective antiparasitic drugs.     

海洛因及补偿AMP和GMP对大鼠海马组织腺苷脱氨酶的影响

目的探讨海洛因及补偿AMP和GMP对海马组织嘌呤核苷酸分解代谢关键酶ADA的影响。方法剂量递增腹腔注射海洛因及嘌呤核苷酸,建立了海洛因及补偿AMP和GMP的给药与依赖大鼠模型,用试剂盒检测海马组织腺苷脱氨酶(ADA)的活性。提取海马组织总RNA,采用逆转录聚合酶链反应检测海马组织ADA mRNA的水平,以β-actin mRNA为内标。结果海马组织中ADA含量测定结果显示,与盐水对照组相比,核苷酸组和海洛因组的海马组织ADA含量明显升高(P0.05,n=10);与海洛因组相比,海洛因加核苷酸组、核苷酸3天组的海马组织ADA含量明显降低(P0.05,n=10),核苷酸9天组降低更为显著(P0.01,n=10)。海马组织中ADA mRNA的水平结果显示,与盐水对照组相比,海洛因组ADA mRNA的相对表达量明显增高(P0.05,n=3),其余各组与盐水对照组相比无统计学意义;与海洛因组相比,海洛因加核苷酸组、戒断3天组、戒断9天组、核苷酸3天组和核苷酸9天组ADA mRNA的相对表达量明显降低(P0.01,n=3)。结论海洛因通过影响海马组织ADA的活性,进而促进嘌呤核苷酸的分解代谢,嘌呤核苷酸和/或代谢产物可能通过某些机制影响海洛因对海马组织的作用,其机制有待进一步研究。     

Liquid chromatography with multichannel ultraviolet detection used for studying disorders of purine metabolism

We used a reversed-phase "high-performance" liquid-chromatographic system equipped with a multichannel ultraviolet spectrometric detector and a micro-computer for analyzing urine samples from patients with disorders of purine metabolism. This system recorded a series of absorption-spectrum data from a single chromatographic run and stored them for subsequent analysis. Because the retention times and ultraviolet absorption spectra of the eluates were recorded simultaneously, identification of peaks was easy and quite accurate for simultaneous quantification of orotidine, adenine, hypoxanthine, uric acid, xanthine, allopurinol (4-hydroxypyrazolo[3,4-d]pyrimidine), oxypurinol (4,6-dihydroxypyrazolo[3,4-d]pyrimidine), inosine, and 2,8-dihydroxyadenine--compounds extremely difficult or even impossible to quantify simultaneously with a conventional single-wavelength spectrometer. We used this method to investigate purine metabolites in urines from a patient with hereditary xanthinuria, three patients with 2,8-dihydroxyadenine urolithiasis, and a gouty subject taking allopurinol.     

The influence of dietary purines and pyrimidines on purine

Allopurinol-induced orotaciduria is reduced by dietary ribonucleic acid (RNA), RNA hydrolysate and different nucleotides. These findings are compatible with feedback regulation of pyrimidine biosynthesis by dietary nucleotides. Serum uric acid and urinary uric acid excretion on a purine-free isoenergetic diet reach a minimum after about 10 days and remain constant thereafter. When purines from different biochemical sources are added to such a diet there is always a linear relationship between dietary purines and serum uric acid level and urinary uric acid excretion. The findings suggest that dietary purines play a minor role if any in the regulation of purine biosynthesis in man.     

Hypoxanthine phosphoribosyltransferase from Trypanosoma cruzi as a target for structure-based inhibitor design: crystallization and inhibition studies with purine analogs.

The hypoxanthine phosphoribosyltransferase (HPRT) from Trypanosoma cruzi is a potential target for enzyme structure-based inhibitor design, based on previous studies which indicate that these parasites lack the metabolic enzymes required for de novo synthesis of purine nucleotides. By using a bacterial complement selection system, 59 purine analogs were assayed for their interaction with the HPRTs from T. cruzi and Homo sapiens. Eight compounds were identified from the bacterial assay to have an affinity for the trypanosomal enzyme. Inhibition constants for four of these compounds against purified recombinant trypanosomal and human HPRTs were determined and compared. The results confirm that the recombinant system can be used to identify compounds which have affinity for the trypanosomal HPRT. Furthermore, the results provide evidence for the importance of chemical modifications at positions 6 and 8 of the purine ring in the binding of these compounds to the HPRTs. An accurate three-dimensional structure of the trypanosomal enzyme will greatly enhance our understanding of the interactions between HPRTs and these compounds. Toward this end, crystallization conditions for the trypanosomal HPRT and preliminary analysis of X-ray diffraction data to a resolution of 2 A is reported. These results represent significant progress toward a structure-based approach to the design of inhibitors of the HPRT of trypanosomes with the long-range goal of developing new drugs for the treatment of Chagas' disease.     

嘌呤核苷酸补偿对海洛因依赖大鼠嘌呤核苷酸代谢相关酶基因表达的影响

目的探讨外源性补偿嘌呤核苷酸对海洛因依赖大鼠嘌呤核苷酸代谢酶的影响。方法将50只雄性Wis-tar大鼠随机分为对照组、海洛因组、海洛因+AMP+GMP组、海洛因+AMP组、海洛因+GMP组。采用real-timePCR的方法检测大鼠脑皮质中腺苷脱氨酶(ADA)、黄嘌呤氧化酶(XO)、次黄嘌呤-鸟嘌呤磷酸核糖转移酶(HGPRT)、腺嘌呤磷酸核糖转移酶(APRT)和腺苷激酶(AK)mRNA的表达水平。结果海洛因组ADA、XO的mRNA比对照组明显升高(P0.05),而海洛因+AMP+GMP组、海洛因+AMP组、海洛因+GMP组与海洛因组相比明显降低(P0.05)。海洛因组HGPRT、APRT和AK的mRNA比对照组明显降低(P0.05),而海洛因+AMP+GMP组、海洛因+AMP组、海洛因+GMP组与海洛因组相比有不同程度升高,以HGPRT的升高程度尤为显著(P0.05)。海洛因+AMP+GMP组、海洛因+AMP组、海洛因+GMP组的各项指标差异无显著性。结论海洛因在大鼠基因水平上促进嘌呤核苷酸的分解代谢,降低合成代谢,而补偿嘌呤核苷酸可以抑制或拮抗海洛因的上述作用。     

STUDIES ON THE MODE OF ACTION OF DIPHTHERIA TOXIN : IV. SPECIFICITY OF THE COFACTOR (NAD) REQUIREMENT FOR TOXIN ACTION IN CELL-FREE SYSTEMS

The ability of a number of nucleotides related to NAD to replace NAD as cofactors for inhibition by diphtheria toxin of peptide bond formation has been examined. Neither NADH nor NADP are active. Of some 14 analogues closely related structurally to NAD that have been tested, only 3-thiocarboxamide pyridine-AD is as active as NAD itself. Replacement of the 3-carboxamide group on the pyridine ring by an acetyl group, or deamination of the purine ring, resulted in derivatives with reduced activity. The results were interpreted as suggesting that NAD and certain related nucleotides are capable of specific interaction with diphtheria toxin. Using the method of equilibrium dialysis, reversible binding of 1 mole of NAD per mole of toxin has been demonstrated. Toxoid does not interact with NAD.     

Purine analogs as chemotherapeutic agents in leishmaniasis and American trypanosomiasis

The metabolic pathways for purines in parasitic protozoans differ significantly from the corresponding pathways in human beings. Leishmania and Trypanosoma cruzi have particular enzymatic reactions that have relevance for chemotherapy. Certain purine analogs are metabolized by the parasites to nucleotides and aminated to the analogs of adenine nucleotides. These halt protein synthesis and cause the break-down of RNA. The most important purine analogs with respect to chemotherapeutic potential are the pyrazolo [3,4-D]-pyrimidines. The prototype, allopurinol, is nontoxic to human beings and is aminated to adenine nucleotide analogs by the organism. Studies in vitro and in vivo have demonstrated its antiparasitic action and led to its development as a chemotherapeutic agent for diseases caused by these organisms. Clinical investigations now have demonstrated the therapeutic efficacy of allopurinol in cutaneous leishmaniasis caused by Leishmania braziliensis and in chronic Chagas' Disease.     

Variations in purine metabolism of cultured skin fibroblasts from patients with gout

Purine metabolism was studied in fibroblasts cultured from three patients with gout in an attempt to determine the biochemical bases of their disease. The rate of purine biosynthesis de novo was normal in one line of cells, but the rate of catabolism of adenine nucleotides to hypoxanthine and inosine was greatly increased. The rate of purine biosynthesis de novo was increased in two lines of cells, and this was associated with increased concentrations of 5-phosphoribosyl 1-pyrophosphate. Purine synthesis was also less sensitive than normal to feedback inhibition. The catabolism of inosinate synthesized de novo was increased.     

Determination of the effects of mycophenolic acid on the nucleotide pool of human peripheral blood mononuclear cells in vitro by high-performance liquid chromatography

Immunosuppressive drugs are needed to prevent the rejection of transplanted organs by the immune system. Immunosuppressive antimetabolites act by interrupting cell metabolism. Their mechanism of action can be studied in vitro by measuring the inhibition of biochemical activities which is reflected by changes in the nucleotide content. In our experiments, human peripheral blood mononuclear cells (PBMC) isolated from healthy volunteers were used. After PBMC stimulation with phytohaemagglutinin (PHA) to mimic activation occurring at a rejection crisis, cells were exposed to varying concentrations of different immunosuppressants (i.e., mycophenolic acid, cyclosporin A and prednisolone) for 68 h at 37 degrees C. Changes in nucleotide content were observed by determining the concentrations of 15 nucleotides using a newly developed HPLC method. The results obtained for mycophenolic acid (MPA; final concentrations in a range between 0.1 and 5 micromol/l), cyclosporin A (CsA; final concentrations between 100 ng/ml and 1 microg/ml) and prednisolone (final concentrations between 0.5 and 10 micromol/l) are given as percentage changes in nucleotide content versus controls and are expressed as mean +/- confidence interval. The possibility of synergistic effects was investigated by incubating the cells with mixtures of all three immunosuppressive drugs varying the amount of mycophenolic acid. In addition, we have shown the effects of MPA/guanosine co-incubation on the intracellular nucleotide levels. Stimulation of peripheral blood mononuclear cells with phytohaemagglutinin led to a significant increase of pyrimidine and purine nucleotides versus control values (100%). Pyrimidine (CTP, UDP, UTP) and purine nucleotides (GDP, GTP, ADP, ATP) were elevated up to 153+/-14% and 142+/-17%, respectively. Under co-incubation of cells with MPA, the GTP level decreased in a dose-related manner to 56+/-3% of control at a MPA final concentration of 5 micromol/l. Concomitantly, an increase of UTP values to 203+/-18% versus control was observed under co-incubation with 1 micromol/l MPA. Co-incubation of mononuclear cells with guanosine (50 micromol/l) compensated for the effects of MPA on intracellular GTP levels. Combination of MPA, CsA and prednisolone did not alter intracellular nucleotide profiles of PBMC compared to those under MPA incubation alone. The depletion of the guanine nucleotide pool and concomitant increase of uridine nucleotides under the influence of the immunosuppressive drug mycophenolic acid is caused by its inhibitory effects on the key enzyme of de novo purine biosynthesis, inosine 5'-monophosphate dehydrogenase (IMPDH).     

Hereditary xanthinuria. Evidence for enhanced hypoxanthine salvage

We tested the hypothesis that there is an enhanced rate of hypoxanthine salvage in two siblings with hereditary xanthinuria. We radiolabeled the adenine nucleotide pool with [8-14C]adenine and examined purine nucleotide degradation after intravenous fructose. The cumulative excretion of radioactivity during a 5-d period was 9.7% and 9.1% of infused radioactivity in the enzyme-deficient patients and 6.0 +/- 0.7% (mean +/- SE) in four normal subjects. Fructose infusion increased urinary radioactivity to 7.96 and 9.16 X 10(6) cpm/g creatinine in both patients and to 4.73 +/- 0.69 X 10(6) cpm/g creatinine in controls. The infusion of fructose increased total urinary purine excretion to a mean of 487% from low-normal baseline values in the patients and to 398 +/- 86% in control subjects. In the enzyme-deficient patients, the infusion of fructose elicited an increase of plasma guanosine from undetectable values to 0.7 and 0.9 microM. With adjustments made for intestinal purine loss, these data support the hypothesis that there is enhanced hypoxanthine salvage in hereditary xanthinuria. Degradation of guanine nucleotides to xanthine bypasses the hypoxanthine salvage pathway and may explain the predominance of this urinary purine compound in xanthinuria.     

Disruption of the Purine Nucleotide Cycle: A POTENTIAL EXPLANATION FOR MUSCLE DYSFUNCTION IN MYOADENYLATE DEAMINASE DEFICIENCY

A patient with symptoms of easy fatigability, postexercise myalgias, and delayed recovery of muscle strength after activity is described. Skeletal muscle from this patient had <1.0% normal myoadenylate deaminase activity and NH₃ was not released from muscle after ischemic exercise. In association with this enzyme deficiency, exercise led to a >90% reduction in muscle content of adenine nucleotides. No inosine monophosphate accumulated after exercise and total purine content of the muscle fell to 21% of control. Repletion of the adenine nucleotide pool in this patient was delayed compared to controls, and ATP content had only returned to 68% of control at 165 min after exercise. These studies demonstrate that disruption of the purine nucleotide cycle as a consequence of myoadenylate deaminase deficiency results in marked alterations in ATP content of muscle, and potentially, these changes in ATP content could account for muscle dysfunction in this patient.