Adenine Nucleotide Synthesis Research Articles

Childhood-Onset Myopathy With Preserved Ambulation Caused by a Recurrent ADSSL1 Missense Variant.

Distal myopathies are a heterogeneous group of primary muscle disorders with recessive or dominant inheritance. ADSSL1 is a muscle-specific adenylosuccinate synthase isoform involved in adenine nucleotide synthesis. Recessive pathogenic variants in the ADSSL1 gene located in chromosome 14q32.33 cause a distal myopathy phenotype. In this study, we present the clinical and genetic attributes of 6 Indian patients with this myopathy. This was a retrospective study describing on Indian patients with genetically confirmed ADSSL1 myopathy. Details were obtained from the medical records. All patients presented in their first or early second decade. All had onset in the first decade with a mean age at presentation being 17.7 ± 8.4 years (range: 3-27 years) and M:F ratio being 1:2. The mean disease duration was 9.3 ± 5.2 years ranging from 2 to 15 years. All patients were ambulant with wheelchair bound state in 1 patient due to respiratory involvement. The median serum creatine kinase (CK) level was 185.5 IU/L (range: 123-1564 IU/L). In addition to salient features of ptosis, cardiac involvement, bulbar weakness, and proximo-distal limb weakness with fatigue, there were significant seasonal fluctuations and decremental response to repetitive nerve stimulation, which have not been previously reported. Muscle histopathology was heterogenous with the presence of rimmed vacuoles, nemaline rods, intracellular lipid droplets along with chronic myopathic changes. Subtle response to pyridostigmine treatment was reported. While 5 of 6 patients had homozygous c.781G>A (p.Asp261Asn) variation, 1 had homozygous c.794G>A (p.Gly265Glu) in ADSSL1 gene. This study expands the phenotypic spectrum and variability of ADSSL1 myopathy with unusual manifestations in this rare disorder. Because the variant c.781G>A (p.Asp261Asn) is the most common mutation among Indian patients similar to other Asian cohorts, this finding could be useful for genetic screening of suspected patients.

Integrated Functions of Cardiac Energetics, Mechanics, and Purine Nucleotide Metabolism.

Purine nucleotides play central roles in energy metabolism in the heart. Most fundamentally, the free energy of hydrolysis of the adenine nucleotide adenosine triphosphate (ATP) provides the thermodynamic driving force for numerous cellular processes including the actin-myosin crossbridge cycle. Perturbations to ATP supply and/or demand in the myocardium lead to changes in the homeostatic balance between purine nucleotide synthesis, degradation, and salvage, potentially affecting myocardial energetics and, consequently, myocardial mechanics. Indeed, both acute myocardial ischemia and decompensatory remodeling of the myocardium in heart failure are associated with depletion of myocardial adenine nucleotides and with impaired myocardial mechanical function. Yet there remain gaps in the understanding of mechanistic links between adenine nucleotide degradation and contractile dysfunction in heart disease. The scope of this article is to: (i) review current knowledge of the pathways of purine nucleotide depletion and salvage in acute ischemia and in chronic heart disease; (ii) review hypothesized mechanisms linking myocardial mechanics and energetics with myocardial adenine nucleotide regulation; and (iii) highlight potential targets for treating myocardial metabolic and mechanical dysfunction associated with these pathways. It is hypothesized that an imbalance in the degradation, salvage, and synthesis of adenine nucleotides leads to a net loss of adenine nucleotides in both acute ischemia and under chronic high-demand conditions associated with the development of heart failure. This reduction in adenine nucleotide levels results in reduced myocardial ATP and increased myocardial inorganic phosphate. Both of these changes have the potential to directly impact tension development and mechanical work at the cellular level. © 2024 American Physiological Society. Compr Physiol 14:5345-5369, 2024.

Hypoxanthine Reduces Radiation Damage in Vascular Endothelial Cells and Mouse Skin by Enhancing ATP Production via the Salvage Pathway

An effective method that can protect radiation-damaged tissues from apoptosis and promote tissue repair has not been reported to date. Hypoxanthine (Hx) is an intermediate metabolite in the purine degradation system that serves as a substrate for ATP synthesis via the salvage pathway. In this study, we focused on the transient decrease in intracellular ATP concentration after radiation exposure and examined the protective effect of Hx against radiation-induced tissue damage. Human umbilical vein endothelial cells were X irradiated, and the cell viability and incidence of apoptosis and DNA double-strand breaks (DSBs) were evaluated at different Hx concentrations. We found that in the presence of 2-100 µM Hx, the percentages of DSBs and apoptotic cells after 2, 6 and 10 Gy dose of radiation significantly decreased, whereas cell viability increased in a concentration-dependent manner. Moreover, the addition of Hx increased the levels of AMP, ADP, and ATP in the cells at 2 h postirradiation, suggesting that Hx was used for adenine nucleotide synthesis through the salvage pathway. Administration of a xanthine oxidoreductase inhibitor to a mouse model of radiation dermatitis resulted in increased blood Hx levels that inhibited severe dermatitis and accelerated recovery. In conclusion, the findings provide evidence that increasing the levels of Hx to replenish ATP could be an effective strategy to reduce radiation-induced tissue damage and elucidating the detailed mechanisms underlying the protective effects of Hx could help develop new protective strategies against radiation.

IMPDH dysregulation in disease: a mini review.

Inosine-5′-monophosphate dehydrogenase (IMPDH) is a highly conserved enzyme in purine metabolism that is tightly regulated on multiple levels. IMPDH has a critical role in purine biosynthesis, where it regulates flux at the branch point between adenine and guanine nucleotide synthesis, but it also has a role in transcription regulation and other moonlighting functions have been described. Vertebrates have two isoforms, IMPDH1 and IMPDH2, and point mutations in each are linked to human disease. Mutations in IMPDH2 in humans are associated with neurodevelopmental disease, but the effects of mutations at the enzyme level have not yet been characterized. Mutations in IMPDH1 lead to retinal degeneration in humans, and recent studies have characterized how they cause functional defects in regulation. IMPDH1 is expressed as two unique splice variants in the retina, a tissue with very high and specific demands for purine nucleotides. Recent studies have revealed functional differences among splice variants, demonstrating that retinal variants up-regulate guanine nucleotide synthesis by reducing sensitivity to feedback inhibition by downstream products. A better understanding of the role of IMPDH1 in the retina and the characterization of an animal disease model will be critical for determining the molecular mechanism of IMPDH1-associated blindness.

Formate induces a metabolic switch in nucleotide and energy metabolism

Formate is a precursor for the de novo synthesis of purine and deoxythymidine nucleotides. Formate also interacts with energy metabolism by promoting the synthesis of adenine nucleotides. Here we use theoretical modelling together with metabolomics analysis to investigate the link between formate, nucleotide and energy metabolism. We uncover that endogenous or exogenous formate induces a metabolic switch from low to high adenine nucleotide levels, increasing the rate of glycolysis and repressing the AMPK activity. Formate also induces an increase in the pyrimidine precursor orotate and the urea cycle intermediate argininosuccinate, in agreement with the ATP-dependent activities of carbamoyl-phosphate and argininosuccinate synthetase. In vivo data for mouse and human cancers confirms the association between increased formate production, nucleotide and energy metabolism. Finally, the in vitro observations are recapitulated in mice following and intraperitoneal injection of formate. We conclude that formate is a potent regulator of purine, pyrimidine and energy metabolism.

Formate Induces a Metabolic Switch in Nucleotide and Energy Metabolism

Formate is a precursor for the de novo synthesis of purine and deoxythymidine nucleotides. Formate also interacts with energy metabolism by promoting the synthesis of adenine nucleotides. Here we use theoretical modelling together with metabolomics analysis to investigate the link between formate, nucleotide and energy metabolism. We uncover that endogenous or exogenous formate induces a metabolic switch from low to high adenine nucleotide levels, increasing the rate of glycolysis and repressing the AMPK activity. Formate also induces an increase in the pyrimidine precursor orotate and the urea cycle intermediate argininosuccinate, in agreement with the ATP dependent activities of carbamoyl-phosphate and argininosuccinate synthetase. In vivo data for mouse and human cancers confirms the association between increased formate production, nucleotide and energy metabolism. Finally, the in vitro observations are recapitulated in mice following intraperitoneal injection of formate. We conclude that formate is a potent regulator of purine, pyrimidine and energy metabolism.

Differential adenosine uptake in mixed neuronal/glial or purified glial cultures of avian retinal cells: Modulation by adenosine metabolism and the ERK cascade

Adenosine is an important modulator of neuronal survival and differentiation in the CNS. Our previous work showed that nucleoside transporters (NTs) are present in cultures of chick retinal cells, but little is known about the mechanisms regulating adenosine transport in these cultures. Our aim in the present work was to study the participation of the adenosine metabolism as well as the ERK pathway on adenosine uptake in different types of retinal cultures (mixed and purified glial cultures). Kinetic analysis in both cultures revealed that the uptake reached equilibrium after 30min and presented two components. Incubation of cultures with S-(p-nitrobenzyl)-6-thioinosine (NBTI) or dipyridamole, different inhibitors of equilibrative nucleoside transporters (ENTs), produced a significant and concentration-dependent uptake reduction in both cultures. However, while dipyridamole presented similar maximal inhibitory effects in both cultures (although in different concentrations), the inhibition by NBTI was smaller in glial cultures than in mixed cultures, suggesting the presence of different transporters. Moreover, pre-incubation of [3H]-adenosine with adenosine deaminase (ADA) or adenosine kinase (ADK) inhibition with iodotubercidin promoted significant uptake inhibition in both cultures, indicating that the uptake is predominantly for adenosine and not inosine, and that taken up adenosine is preferentially directed to the synthesis of adenine nucleotides. In both cultures, the MEK inhibitors PD98059 or UO126, but not the inactive analog U0124, induced a significant and concentration-dependent uptake decrease. We have not observed any change in adenosine metabolism induced by MEK inhibitors, suggesting that this pathway is mediating a direct effect on NTs. Our results show the expression of different NTs in retinal cells in culture and that the activity of these transporters can be regulated by the ERK pathway or metabolic enzymes such as ADK which are then potential targets for regulation of Ado levels in normal or pathological conditions.

Fine control of caffeine biosynthesis in tissue cultures of Camellia sinensis

To determine whether caffeine biosynthesis is controlled by the availability of purine precursors and/or methyl-donors, we examined the effect of some purine compounds on purine alkaloid accumulation, using tea callus cultures. No stimulation of caffeine biosynthesis was observed when the calli were cultured with 0.5 mM adenosine, guanosine or hypoxanthine for 3 weeks. However, 0.5 mM paraxanthine doubled the caffeine level relative to controls. Adenosine stimulated the growth of callus and reduced the caffeine concentration 3 months after inoculation. These results indicate that methylation of xanthosine by 7-methylxanthosine synthase is the most plausible rate-limiting step of caffeine biosynthesis; the supply of non-methylated purine precursors or availability of S-adenosyl- l-methionine are not the principal controlling factors of caffeine biosynthesis. Adenosine salvage to adenine nucleotide synthesis may contribute to the growth of tea calli, but not to caffeine biosynthesis.

Metabolism of nicotinamide, adenine and inosine in developing microspore-derived canola (Brassica napus) embryos

The metabolic fate of [carbonyl-(14)C]nicotinamide, [8-(14)C]adenine and [8-(14)C]inosine was examined in microspore-derived canola (Brassica napus) embryos at different developmental stages: globular stage (day 10, stage 1), early cotyledonary stage (day 20, stage 2), late cotyledonary stage (day 25, stage 3), and fully developed stage (day 35, stage 4). Uptake of [8-(14)C]nicotinamide by the embryos was always rapid. A lower uptake rate was found for [8-(14)C]adenine and [8-(14)C]inosine, especially at stages 1 and 2. [Carbonyl-(14)C]nicotinamide was converted to nicotinic acid and further metabolized to pyridine nucleotides (NAD/NADP). Some radioactivity was also associated to nicotinic acid glucoside. [8-(14)C]adenine was efficiently utilized for the synthesis of adenine nucleotides and RNA. A small fraction of adenine was degraded to CO(2) via ureides. Up to 40% of [8-(14)C]inosine was salvaged to nucleotides and RNA, although degradation of [8-(14)C]inosine to CO(2) was pronounced. At stage 1, highest salvage activities of nicotinamide, adenine and inosine were observed. In contrast, the lowest purine salvage and highest purine catabolism were found in stage 3 embryos. These results suggest that both nicotinamide and purine salvage for NAD/NADP and purine nucleotides synthesis are extremely high in the globular stage (stage 1). These activities decrease gradually until the late cotyledonary stage (stage 3), before increasing again in the fully developed embryos (stage 4). Overall it appears that nicotinamide and purine salvage are required in support of active growth during the initial phases of embryogenesis and at the end of the maturation period, in preparation for post-embryonic growth.

Metabolic fate of nicotinamide in higher plants

Metabolism of [carbonyl-14C]nicotinamide was surveyed in various plant materials including the model plants, Arabidopsis thaliana, Oryza sativa and Lotus japonicus. In all plants studied, nicotinamide was used for the pyridine (nicotinamide adenine) nucleotide synthesis, probably after conversion to nicotinic acid. Radioactivity from [carbonyl-14C]nicotinamide was incorporated into trigonelline (1-N-methylnicotinic acid) and/or into nicotinic acid 1N-glucoside (Na-Glc). Trigonelline is formed mainly in leaves and cell cultures of O. sativa and L. japonicus and in seedlings of Trifolium incarnatum, Medicago sativa and Raphanus sativus. Trigonelline synthesis from nicotinamide is generally greater in leaves than in roots. Na-Glc was formed as the major nicotinic acid conjugate in A. thaliana and in tobacco Bright Yellow-2 cells. In seedlings of Chrysanthemum coronarium and Theobroma cacao, both trigonelline and Na-Glc were synthesized from [carbonyl-14C]nicotinamide. Trigonelline is accumulated in some seeds, mainly Leguminosae species. The pattern of formation of the nicotinic acid conjugates differs between species and organs.

Cerulenin-mediated apoptosis is involved in adenine metabolic pathway

Cerulenin, a fatty acid synthase (FAS) inhibitor, induces apoptosis of variety of tumor cells. To elucidate mode of action by cerulenin, we employed the proteomics approach using Schizosaccharomyces pombe. The differential protein expression profile of S. pombe revealed that cerulenin modulated the expressions of proteins involved in stresses and metabolism, including both ade10 and adk1 proteins. The nutrient supplementation assay demonstrated that cerulenin affected enzymatic steps transferring a phosphoribosyl group. This result suggests that cerulenin accumulates AMP and p-ribosyl- s-amino-imidazole carboxamide (AICAR) and reduces other necessary nucleotides, which induces feedback inhibition of enzymes and the transcriptional regulation of related genes in de novo and salvage adenine metabolic pathway. Furthermore, the deregulation of adenine nucleotide synthesis may interfere ribonucleotide reductase and cause defects in cell cycle progression and chromosome segregation. In conclusion, cerulenin induces apoptosis through deregulation of adenine nucleotide biosynthesis resulting in nuclear division defects in S. pombe.

Intense exercise induces the degradation of adenine nucleotide and purine nucleotide synthesis via de novo pathway in the rat liver

The purpose of this study was to investigate the influence of intense exercise on the metabolism of adenine nucleotides in the liver. In the first experiment, to determine the degradation of adenine nucleotides, hepatic adenine nucleotides of rats were labeled by an intraperitoneal administration of 15N-labeled adenine the day before treadmill running to exhaustion. In the second experiment, to determine the de novo synthesis of purine nucleotides after intense exercise, 14C-glycine was intraperitoneally administered to rats performing intense running on a treadmill. In the first experiment, hepatic levels of ATP and total adenine nucleotides showed a reduction immediately after exercise. In contrast, hepatic levels of AMP, adenosine, hypoxanthine and uric acid showed an increase immediately after exercise. The hepatic 15N level continued to decline during the recovery period after exercise. Urinary excretion of 15N-urate was 40% higher in the exercised rats than in the control rats. In the second experiment, the radioactivity of 14C detected in the fraction of hepatic urate and allantoin was approximately 300% higher in the exercised rats than in the control rats. 14C-radioactivity that excreted into urine as urate and allantoin was approximately 200% higher in the exercised rats. Intense exercise led to the degradation of hepatic adenine nucleotides, which were not utilized for the re-synthesis of nucleotide and further degraded to hypoxanthine or uric acid. Intense exercise induced the synthesis of purine nucleotides in the liver via a de novo pathway and these synthesized nucleotides were also degraded to nucleosides and excreted into urine.

AMP Deaminase Activation Contributes to Accelerated Adenine Nucleotide Pool Depletion during Periods of Energy Imbalance in Sickle Cell Erythrocytes.

Mature erythrocytes are unable to synthesize AMP from IMP due to the developmental loss of adenylosuccinate synthetase, which also effectively prevents the synthesis of adenine nucleotides from circulating hypoxanthine, the major salvageable purine compound. Consequently, AMP deaminase (AMPD) activity must be tightly regulated in order to avoid irreversible depletion of the erythrocyte adenine nucleotide pool during periods of energy imbalance. However, increased intracellular calcium promotes activation of erythrocyte AMPD (AMPD3) through a protein-protein interaction with calmodulin (Mahnke and Sabina, Biochemistry 44:5551, 2005). Therefore, we hypothesized that Sickle Cell Disease (SCD) erythrocytes would more rapidly accumulate IMP and deplete the adenine nucleotide pool during periods of energy imbalance. In order to test this hypothesis, acid-soluble pools of these metabolites were quantified by anion-exchange HPLC in SCD and control erythrocytes during autoincubation and glucose starvation, both at 37C. Data in the table show that SCD erythrocytes accumulate more IMP during a 6-hour autoincubation compared to control cells, and this is accompanied by a decrease in AMP.Effect of Autoincubation on Erythrocyte AMP and IMP PoolsGROUPHOURSAMPaIMPIMP/AMPControl (N=4)0.29±.08.15±.06.58±.286.29±.01.33±.11†1.15±.35†SCD (N=5)0.22±.04.08±.03.36±.106.14±.03†.74±.24†‡5.15±1.25†‡a, metabolite concentrations reported as μmol/g Hb; †, p<.05 when compared to 0 time in a paired student's t-test; ‡, p<.05 when compared to control in an unpaired student's t-testData in the figure show an accelerated depletion of ATP and increased accumulation of IMP in glucose-starved SCD erythrocytes compared to control cells (*, p<.05 when compared to control in an unpaired student's t-test). [Display omitted] These combined results demonstrate AMPD3 enzyme activation and accelerated adenine nucleotide pool depletion during periods of energy imbalance in SCD erythrocytes. This metabolic imbalance in SCD erythrocytes could contribute to 1) an increased rate of hemolysis, 2) cation channel dysregulation, 3) modulation of adhesive membrane components, and 4) diminished protein phosphorylation. Furthermore, strategies directed against this metabolic imbalance, e.g., diffusible AMPD inhibitors and adenine supplementation, may have a therapeutic benefit in SCD.

Abiogenic photochemical synthesis on surface of meteorites and other small space bodies

Abstract The abiogenic photochemical synthesis of complex biochemical compounds on the surface of small bodies in our Solar system was examined. Hydrated minerals are found within a chondrite matrix of meteorites together with significant amounts of organic matter. Clays are likely to have formed when water was present on parent meteoritic bodies. In order to verify the existence of a relationship between abiogenic synthesis of nucleotides and inorganic components of the meteorites, we have investigated possible abiogenic reactions associated with different clay (montmorillonite, kaolinite) and a basaltic one (Tyatya’s volcanic ash) under action of open space energy sources as a model of different exobiological environments on the surface of small space bodies. The abiogenic synthesis of natural adenine nucleotides from a mixture of adenosine and inorganic phosphate has been observed following irradiation with VUV light in the presence of different mineral samples. The yields of the products (5′AMP, 2′AMP, 3′AMP, 2′3′cAMP and 3′5′cAMP) depended on irradiation time and kinds of minerals used. The discovery that meteoritic organic compounds may be trapped and protected within a clay mineral matrix has implications for our understanding of prebiotic molecular evolution in the early Solar system. Clay minerals may also have concentrated organic compounds thereby promoting polymerization reactions. An adsorption/binding of nucleic acids components by clay crystals could change the electron distribution and/or the conformation of the molecules. The remnant water molecules in the clay sheets also could influence the course of the reaction. Clay immobilization of phosphate could play an important role in this reaction. Chondritic material could have been a common component of the inner Solar system shortly after its formation and the biologically useful products of clay mineral–organic matter interactions could have also widespread, and delivered to planetary surfaces through the accretion of carbonaceous asteroids.

Benefit of Ribose in a Patient with Fibromyalgia

Ribose was added to the existing treatment regimen of a woman with fibromyalgia, resulting in a decrease in symptoms. It has been postulated that patients with fibromyalgia may have an alteration in muscle adenine nucleotide metabolism, leading to depleted energy reserves and an imbalance in cellular adenosine 5'-triphosphate:adenosine 5'-diphosphate:adenosine 5'-monophosphate (ATP:ADP:AMP) ratios with an abnormal energy charge. As a key component in adenine nucleotide synthesis, ribose supplementation may be useful in such patients.

Unique kinetic mechanism of Plasmodium falciparum adenylosuccinate synthetase

Adenylosuccinate synthetase (AdSS) catalyses the Mg(2+) dependent formation of adenylosuccinate from IMP and aspartate, the reaction being driven by the hydrolysis of GTP to GDP. All characterized AdSS thus far exhibit a random kinetic mechanism. We present here kinetic evidence that unlike all other AdSS, Plasmodium falciparum AdSS (PfAdSS) has ordered substrate binding. Inhibition studies show that binding of GTP requires IMP binding while aspartate binds to the enzyme-IMP-GTP complex. A structural basis for this difference in mechanism is presented. Kinetically, PfAdSS is closer to the mouse acidic isozyme rather than to the mouse basic isozyme. The mouse acidic isozyme is thought to play a role in the purine nucleotide biosynthetic pathway. Regulation of PfAdSS in vivo can therefore, be expected to be similar to the mouse acidic isozyme, in agreement with the role of PfAdSS as the only pathway for the synthesis of adenine nucleotides in the parasite. However, PfAdSS differs from both the mammalian homologs in that fructose-1,6-bisphosphate, a potent inhibitor of the mammalian enzyme, is an activator of PfAdSS. The differences highlighted here are promising in terms of species-specific drug design, targeting this essential enzyme in the parasite.

Zinc inhibition of hepatic fructose metabolism in rats.

The ability of Zn to modulate key metabolic processes was investigated in a study of gluconeogenesis in isolated hepatocytes from fasted rats. Zn (100 microM) inhibited glucose production from fructose by 41%, sorbitol by 28%; glycerol by 17%, and glyceraldehyde by 26%. Maximum inhibition of gluconeogenesis from fructose occurred at 25 microM Zn. Zn inhibited the rate of lactate production from fructose by 24% but not from sorbitol, glycerol, or glyceraldehyde. Fructose uptake by hepatocytes was not affected by Zn. A positive linear relationship (r=0.994) was obtained between inhibition by Zn of glucose and lactate production, indicating that a common step in both pathways is inhibited by Zn. The effect of Zn on fructokinase, aldolase-B, and triokinase activities was determined on semipurified rat liver enzyme preparations. Zn had no affect on triokinase activity but inhibited the two other enzymes in a dose-dependent manner, with the inhibition of aldolase-B being much greater than of fructokinase for concentrations of Zn between 2.5 and 20 microM. Zn increased the intracellular concentration of fructose-1-P in hepatocytes incubated with fructose, indicating a more potent Zn inhibition of aldolase-B than fructokinase. In addition, hepatocytes treated with Zn had decreased ATP and ADP concentrations, but had normal energy charge, suggesting an effect of Zn on adenine nucleotide degradation or synthesis. The demonstration that Zn inhibits two enzymes in fructose metabolism adds to the growing list of metabolic pathways that are catalyzed by enzymes that are sensitive to Zn.

Purine salvage to adenine nucleotides in different skeletal muscle fiber types.

Rates of purine salvage of adenine and hypoxanthine into the adenine nucleotide (AdN) pool of the different skeletal muscle phenotype sections of the rat were measured using an isolated perfused hindlimb preparation. Tissue adenine and hypoxanthine concentrations and specific activities were controlled over a broad range of purine concentrations, ranging from 3 to 100 times normal, by employing an isolated rat hindlimb preparation perfused at a high flow rate. Incorporation of [(3)H]adenine or [(3)H]hypoxanthine into the AdN pool was not meaningfully influenced by tissue purine concentration over the range evaluated (approximately 0.10-1.6 micromol/g). Purine salvage rates were greater (P < 0.05) for adenine than for hypoxanthine (35-55 and 20-30 nmol x h(-1) x g(-1), respectively) and moderately different (P < 0.05) among fiber types. The low-oxidative fast-twitch white muscle section exhibited relatively low rates of purine salvage that were approximately 65% of rates in the high-oxidative fast-twitch red section of the gastrocnemius. The soleus muscle, characterized by slow-twitch red fibers, exhibited a high rate of adenine salvage but a low rate of hypoxanthine salvage. Addition of ribose to the perfusion medium increased salvage of adenine (up to 3- to 6-fold, P < 0.001) and hypoxanthine (up to 6- to 8-fold, P < 0.001), depending on fiber type, over a range of concentrations up to 10 mM. This is consistent with tissue 5-phosphoribosyl-1-pyrophosphate being rate limiting for purine salvage. Purine salvage is favored over de novo synthesis, inasmuch as delivery of adenine to the muscle decreased (P < 0.005) de novo synthesis of AdN. Providing ribose did not alter this preference of purine salvage pathway over de novo synthesis of AdN. In the absence of ribose supplementation, purine salvage rates are relatively low, especially compared with the AdN pool size in skeletal muscle.

Effect of Vacuum Ultraviolet Irradiation on Abiogenous Synthesis of Adenine Nucleotides in the Presence of Lunar Ground

Vacuum ultraviolet (VUV) radiation, a powerful energy source in free Space, have been established to promote synthesis of natural nucleotides. It is shown that lunar ground protects from destruction (up to 1.5–2.0% ) the nucleotides formed after VUV-irradiation of dry films (adenosine and inorganic phosphate). Identification and quantitative determination of the products of synthesis and destruction is performed by the method of high performance liquid chromatography. The following products of synthesis are found: 5'-AMP > 2'3'-cAMP > 2'-AMP > 3'5'-cAMP > 3'-AMP. The obtained results are discussed from the viewpoint of hypothesis about the Space (extraterrestrial) origin of biologically important compounds that were initial for evolution on the Earth.

Adenine Nucleotide Synthesis in Human Erythrocytes Depends on the Mode of Supplementation of Cell Suspension with Adenosine

ABSTRACT: In suspensions of washed human erythrocytes, adenosine added in a single dose to concentrations of 0.1–10.0 mmol/l suspension was deaminated at rates ranging from 10 to 50 mmol/l cells h. The sum of adenosine, inosine, and hypoxanthine concentrations in the suspension, as well as the intracellular concentration of ATP, remained constant. In the presence of 25–50 mmol/l orthophosphate, addition of a single dose of adenosine into erythrocyte suspension increased the ATP concentration by up to 280% of the initial level. If the initial adenosine concentrations were greater than 5 mmol/l suspension, ATP increased independently of adenosine concentration to the level determined only by the concentration of orthophosphate. After orthophosphate was returned to its initial level, ATP in erythrocytes began to decrease. In the presence of coformycin, erythrocytes utilised adenosine at a rate of 0.2–0.3 mmol/l cells h. Their adenylate pool increased at a rate of 0.10–0.16 mmol/l cells h for several hours, but intracellular ATP increased only slightly. The energy charge of cells decreased significantly from 0.86±0.05 (control) to 0.82±0.06. Adenosine continuously pumped into erythrocyte suspensions at rates of 0.02–5.0 mmol/l cells h for several hours caused the adenylate pool of erythrocytes and intracellular ATP to increase synchronously at a rate of 0.02–0.35 mmol/l cells h. The energy charge of these erythrocytes increased significantly up to 0.91±0.03. After pumping of adenosine was stopped, the intracellular ATP and the adenylate pool began to decrease, returning sometimes to the initial level in 2–3 h.