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I Nissim

Publications and source records attributed to I Nissim.

At least 55 records · Page 3Linked to original sources
PubMed1993

Cerebral aspartate utilization: near-equilibrium relationships in aspartate aminotransferase reaction.

The pathways of nitrogen transfer from 50 microM [15N]aspartate were studied in rat brain synaptosomes and cultured primary rat astrocytes by using gas chromatography-mass spectrometry technique. Aspartate was taken up rapidly by both preparations, but the rates of transport were faster in astrocytes than in synaptosomes. In synaptosomes, 15N was incorporated predominantly into glutamate, whereas in glial cells, glutamine and other 15N-amino acids were also produced. In both preparations, the initial rate of N transfer from aspartate to glutamate was within a factor of 2-3 of that in the opposite direction. The rates of transamination were greater in synaptosomes than in astrocytes. Omission of glucose increased the formation of [15N]-glutamate in synaptosomes, but not in astrocytes. Rotenone substantially decreased the rate of transamination. There was no detectable incorporation of 15N from labeled aspartate to 6-amino-15N-labeled adenine nucleotides during 60-min incubation of synaptosomes under a variety of conditions; however, such activity could be demonstrated in glial cells. The formation of 15N-labeled adenine nucleotides was marginally increased by the presence of 1 mM aminooxyacetate, but was unaffected by pretreatment with 1 mM 5-amino-4-imidazolecarboxamide ribose. It is concluded that (1) aspartate aminotransferase is near equilibrium in both synaptosomes and astrocytes under cellular conditions, but the rates of transamination are faster in the nerve endings; (2) in the absence of glucose, use of amino acids for the purpose of energy production increases in synaptosomes, but may not do so in glial cells because the latter possess larger glycogen stores; and (3) nerve endings have a very limited capacity for salvage of the adenine nucleotides via the purine nucleotide cycle.

Adenine Nucleotides↗
PubMed1993

Brain glutamate metabolism: neuronal-astroglial relationships.

The concentration of glutamate in the brain extracellular fluid must be kept low (approximately 3 microM) in order to maximize the signal-to-noise ratio upon the release of glutamate from neurons. In addition, the nerve endings require a supply of glutamate precursors that will not cause depolarization. The major precursor to neuronal glutamate is glutamine, which is synthesized in astrocytes and converted to glutamate in neurons. However, glutamine is not the sole source. Alanine also might serve as a precursor to glutamate via transamination, although this reaction is relatively inactive in synaptosomes. Finally, the branched-chain amino acids, and in particular leucine, appear to be very important precursors to glutamate and glutamine in astrocytes. By providing alpha-NH2 groups for the synthesis of glutamine, leucine also abets the uptake into brain of neutral amino acids, which are transported in exchange for brain glutamine. In addition, the branched-chain ketoacids are readily reaminated to the cognate amino acids, in the process consuming glutamate. Intraneuronal consumption of glutamate via ketoacid reamination might serve to buffer internal [glutamate] and to modulate the releasable pool.

Animals↗
PubMed1993

Acid-base regulation of hepatic glutamine metabolism and ureagenesis: study with 15N.

The metabolism of (5-15N)glutamine and (2-15N) glutamine has been studied by isolated hepatocytes obtained from either control, chronically acidotic, or alkalotic rats. The main goal was to elucidate the mechanism(s) by which altered acid-base state affects hepatic ureagenesis from glutamine. Isolated hepatocytes were incubated in Krebs buffer (pH 7.4) supplemented with 0.1 mM ornithine plus either 1 mM (5-15N)glutamine or (2-15N)glutamine. To elucidate the role of glutamine cycling in net ammonia metabolism, a separate series of experiments were performed with 1 mM unlabeled glutamine plus 1 mM (15N)H4Cl. Net glutamine utilization was significantly lower in hepatocytes obtained from chronically acidotic rats compared with control or alkalotic rats. The sum of the rates of 15NH3 and (15N)urea production from (5-15N)glutamine was decreased in acidosis compared with alkalosis. After incubations of 50 min, approximately 75, 65, or 90% of the N in carbamoyl-phosphate was derived from the 5-N of glutamine in control, acidosis, or alkalosis respectively. In experiments with (2-15N)glutamine, the production of singly and doubly labeled (15N)urea as well as (15N)aspartate and (15N)H3 was significantly smaller in acidosis compared with alkalosis. Furthermore, a correlation was observed between production rates of (15N)aspartate and (15N)urea, suggesting that alterations in urea production may depend on aspartate formed from glutamine. However, the production of (15N)alanine was higher in acidosis compared with alkalosis with apparent correlation between the production of (15N)alanine and 2-oxoglutaramate, a product of the glutamine aminotransferase pathway. In addition, the rate of glutamine recycling was significantly higher in acidosis compared with control or alkalosis, indicating that both flux through glutamine aminotransferase and flux through glutamine synthetase were elevated in acidosis compared with alkalosis. These data suggest that decreased formation of aspartate from glutamine may limit ureagenesis in chronic metabolic acidosis. The formation of aspartate may depend on the availability of oxaloacetate rather than diminished flux through transaminase reaction. The enhancement of alanine production and glutamine synthesis may provide an alternate route of N disposal in cases of diminished urea formation.

Acid-Base Equilibrium↗
PubMed1992

Relative role of the glutaminase, glutamate dehydrogenase, and AMP-deaminase pathways in hepatic ureagenesis: studies with 15N.

We have studied the relative roles of the glutaminase versus glutamate dehydrogenase (GLDH) and purine nucleotide cycle (PNC) pathways in furnishing ammonia for urea synthesis. Isolated rat hepatocytes were incubated at pH 7.4 and 37 degrees C in Krebs buffer supplemented with 0.1 mM L-ornithine and 1 mM [2-15N]glutamine, [5-15N]glutamine, [15N]aspartate, or [15N]glutamate as the sole labeled nitrogen source in the presence and absence of 1 mM amino-oxyacetate (AOA). A separate series of incubations was carried out in a medium containing either 15N-labeled precursor together with an additional 19 unlabeled amino acids at concentrations similar to those of rat plasma. GC-MS was utilized to determine the precursor product relationship and the flux of 15N-labeled substrate toward 15NH3, the 6-amino group of adenine nucleotides ([6-15NH2]adenine), 15N-amino acids, and [15N]urea. Following 40 min incubation with [15N]aspartate the isotopic enrichment of singly and doubly labeled urea was 70 and 20 atom % excess, respectively; with [15N]glutamate these values were approximately 65 and approximately 30 atom % excess for singly and doubly labeled urea, respectively. In experiments with [15N]aspartate as a sole substrate 15NH3 enrichment exceeded that in [6-NH2]adenine, indicating that [6-15NH2]adenine could not be a major precursor to 15NH3. Addition of AOA inhibited the formation of [15N]glutamate, 15NH3 and doubly labeled urea from [15N]aspartate. However, AOA had little effect on [6-15NH2]adenine production. In experiments with [15N]glutamate, AOA inhibited the formation of [15N]aspartate and doubly labeled urea, whereas 15NH3 formation was increased. In the presence of a physiologic amino acid mixture, [15N]glutamate contributed less than 5% to urea-N. In contrast, the amide and the amino nitrogen of glutamine contributed approximately 65% of total urea-N regardless of the incubation medium. The current data indicate that when glutamate is a sole substrate the flux through GLDH is more prominent in furnishing NH3 for urea synthesis than the flux through the PNC. However, in experiments with medium containing a mixture of amino acids utilized by the rat liver in vivo, the fraction of NH3 derived via GLDH or PNC was negligible compared with the amount of ammonia derived via the glutaminase pathway. Therefore, the current data suggest that ammonia derived from 5-N of glutamine via glutaminase is the major source of nitrogen for hepatic urea-genesis.

AMP Deaminase↗
PubMed1992

A mechanism of glycine and alanine cytoprotective action: stimulation of stress-induced HSP70 mRNA.

Studies done both in vitro and in vivo have shown that glycine and alanine protect kidney cells from stress injury. However, the mechanism(s) of this cytoprotection is unknown. Our aim was to test the hypothesis that the cytoprotective action is in part due to stimulation of gene(s) expression encoding stress protein synthesis. Experiments were carried out using heat shock as a model for stress in the opossum kidney cell line (OK cells). The induction of HSP70 mRNA was evaluated in cell monolayers exposed to 45 degrees C for 15 minutes followed by a recovery period at 37 degrees C for either 0.5, 1, 2, 3, 4, 6 or 24 hours. The results demonstrate that the maximum level of HSP70 mRNA occurred at approximately three hours after heat treatment. Although the mRNA levels declined thereafter, appreciable amounts were still seen even 24 hours after heat-shock. To examine the effect of glycine or alanine on HSP70 mRNA levels and on the synthesis of stress protein, cultures were preincubated for 30 minutes with Krebs-Henseleit buffer, pH 7.4, supplemented with either 1, 2, 5 or 10 mM glycine or alanine, or with no added amino acids. Comparative studies were performed with 10 mM glutamate, aspartate, arginine or leucine. Following preincubation, cultures were heat-shocked (45 degrees C for 15 min) and then reincubated at 37 degrees C for three hours. Both glycine and alanine enhanced the level of HSP70 mRNA and the synthesis of 72, 73 kDa stress proteins, but neither amino acid induced HSP70 mRNA without concomitant heat treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed1991

Analysis and physiological implications of renal 2-oxoglutaramate metabolism.

The relative significance of the flux through the glutamine aminotransferase (glutaminase II) pathway to renal ammoniagenesis is poorly understood. A basic and unresolved question is whether 2-oxoglutaramate (2-OGM), a product of the glutaminase II reaction, is deamidated to yield 2-oxoglutarate and NH3, or whether 2-OGM accumulates as an unreactive lactam, depending on the environmental pH. In the current studies we utilized 13C n.m.r. as well as 15N n.m.r. as well as 15N n.m.r. to demonstrate that 2-OGM occurs as a lactam, i.e. 5-hydroxypyroglutamate, regardless of the environmental pH. Our additional aims were to determine whether human kidney cells (HK cells) in culture can produce 2-OGM and to ascertain a pH-dependent relationship between NH3 and 2-OGM production from glutamine. We therefore developed an isotope dilution assay for 2-OGM utilizing 5-hydroxy[4-13C,1-15N]pyroglutamate as the labelled species. Incubations of HK cells in minimal essential medium supplemented with 1 mM-[2-15N]glutamine demonstrated significantly higher production of 2-OGM at pH 6.8 and lower production at pH 7.6 compared with pH 7.4. Similarly both 15NH3 and [15N]alanine formation were significantly higher in acute acidosis (pH 6.8) and lower in acute alkalosis (pH 7.6) compared with that at physiological pH. Addition of 1 mM-amino-oxyacetate to the incubation medium at pH 7.4 significantly diminished [15N]alanine and 2-OGM production, but the production of 15NH3 via the glutamate dehydrogenase pathway was significantly stimulated. The current observations indicate that the glutaminase II pathway plays a minor role and that flux through glutamate dehydrogenase is the predominant site for regulation of ammoniagenesis in human kidney.

Biotransformation↗
PubMed1991

Glutamate dehydrogenase reaction as a source of glutamic acid in synaptosomes.

The role of the glutamate dehydrogenase reaction as a pathway of glutamate synthesis was studied by incubating synaptosomes with 5 mM 15NH4Cl and then utilizing gas chromatography-mass spectrometry to measure isotopic enrichment in glutamate and aspartate. The rate of formation of [15N]glutamate and [15N]aspartate from 5 mM 15NH4Cl was approximately 0.2 nmol/min/mg of protein, a value much less than flux through glutaminase (4.8 nmol/min/mg of protein) but greater than flux through glutamine synthetase (0.045 nmol/min/mg of protein). Addition of 1 mM 2-oxoglutarate to the medium did not affect the rate of [15N]glutamate formation. O2 consumption and lactate formation were increased in the presence of 5 mM NH3, whereas the intrasynaptosomal concentrations of glutamate and aspartate were unaffected. Treatment of synaptosomes with veratridine stimulated reductive amination of 2-oxoglutarate during the early time points. The production of ([15N]glutamate + [15N]aspartate) was enhanced about twofold in the presence of 5 mM beta-(+/-)-2-aminobicyclo [2.2.1]heptane-2-carboxylic acid, a known effector of glutamate dehydrogenase. Supplementation of the incubation medium with a mixture of unlabelled amino acids at concentrations similar to those present in the extracellular fluid of the brain had little effect on the intrasynaptosomal [glutamate] and [aspartate]. However, the enrichment in these amino acids was consistently greater in the presence of supplementary amino acids, which appeared to stimulate modestly the reductive amination of 2-oxoglutarate. It is concluded: (a) compared with the phosphate-dependent glutaminase reaction, reductive amination is a relatively minor pathway of synaptosomal glutamate synthesis in both the basal state and during depolarization; (b) NH3 toxicity, at least in synaptosomes, is not referable to energy failure caused by a depletion of 2-oxoglutarate in the glutamate dehydrogenase reaction; and (c) transamination is not a major mechanism of glutamate nitrogen production in nerve endings.

Amino Acids↗
PubMed1991

Relationships between intracellular amino acid levels and protection against injury to isolated proximal tubules.

Metabolism and cellular levels of glycine, alanine, and other relevant amino acids in proximal tubules were studied during models of acute injury and protection by glycine. Freeze-clamped, normal rabbit renal cortex was very rich in glycine (66.8 nmol/mg protein) and glutamate and also had substantial levels of taurine, alanine, glutamine, serine, and aspartate. Isolated proximal tubules were severely depleted of all these amino acids (glycine, 2.1 nmol/mg protein). During 37 degrees C incubation in presence of alanine, tubules recovered only glutamate to a level approximating that in vivo (38.8 nmol/mg protein, 15.2 mM). Glycine added to medium at levels ranging from 0.25 to 2 mM was actively concentrated four- to sixfold by tubule cells. Two millimolar glycine potently protected tubules from lethal cell injury induced by hypoxia, antimycin A, or ouabain. Glycine levels of injured tubules rapidly equilibrated with medium, irrespective of whether glycine was loaded by preincubation or was added concomitantly with the injury maneuver. Metabolism of glycine during protection, assessed by changes in total levels, gas chromatography-mass spectroscopy determination of the fate of [13C]glycine, and redistribution of label from [3H]glycine was minimal. The data suggest that glycine plays an essential, constitutive role in maintenance of tubule cell structural integrity independently of common metabolic pathways. Intracellular amino acid content is sufficiently labile for depletion of structurally essential amino acids to potentially occur in a variety of settings, but, even with severe ATP depletion or Na+ pump inhibition, supplemental glycine is readily available to intracellular sites of action.

Amino Acids↗
PubMed1991

Pathways of acute pH regulation of ammoniagenesis in LLC-PK1 cells: study with [15N]glutamine.

The present study utilized [15N]glutamine labeled at amide (5-N) and amino (2-N) groups to analyze the metabolic fate of glutamine nitrogen in basal and in acute pH regulation of ammoniagenesis. One-hour incubation of LLC-PK1 cultures in a media of pH 7.4, 7.0, or 7.6 containing either [5-15N]glutamine or [2-15N]glutamine resulted in parallel alterations in glutamine consumption in response to acute acid-base maneuvers. Incubation with [5-15N]glutamine resulted in substantial enrichment and production of ammonia at pH 7.4, which was unaffected by the changes in media pH, and in no significant enrichment of alanine, aspartate, and glutamate. In contrast, significant enrichment and production of 15N-labeled ammonia, alanine, aspartate, and glutamate were detected from cultures incubated with [2-15N]glutamine. Ammonia formation, from incubation with [2-15N]glutamine, was stimulated significantly by a low pH and inhibited by high pH. Alanine production was altered in a fashion similar to ammonia formation, whereas aspartate production was unaltered and glutamate formation significantly decreased by a low pH. Furthermore, a low pH significantly increased the production of alpha-ketoglutaramate in a fashion qualitatively similar to alanine production. In contrast to our prior conclusions based on total metabolite production, these studies indicate that although ammonia formation at pH 7.4 is predominantly generated from the mitochondrial phosphate-dependent glutaminase pathway, the increased ammonia formation in acute acidosis is a result of increased flux through glutamate dehydrogenase.(ABSTRACT TRUNCATED AT 250 WORDS)

Alanine↗
PubMed1991

Adaptation of renal tricarboxylic acid cycle metabolism to various acid-base states: study with [3-13C,5-15N]glutamine.

We studied mechanism(s) by which adaptations of renal TCA cycle metabolism abet ammoniagenesis from glutamine in altered acid-base states. Renal tubules from control, acidotic, or alkalotic rats were incubated at pH 7.4 with 1 mM [3-13C,5-15N]glutamine or 2 mM [3-13C]pyruvate. In acidosis there was a significantly higher flux through glutaminase and through glutamate, 2-oxoglutarate, succinate and malate dehydrogenases as well as markedly enhanced 13C-glucose formation. Alkalosis was associated with little change in 13C flux from glutamine to TCA cycle intermediates compared with control but production of 15NH3 and 13C glucose was significantly diminished. The current studies indicate that renal ammoniagenesis might be regulated at the sites of citrate synthetase (CS) and/or alpha-ketoglutarate dehydrogenase (KGDH). Thus, in chronic metabolic acidosis decreased flux through CS and increased flux through KGDH resulted in enhanced flux through glutamate dehydrogenase and glutaminase pathway. The opposite occurred in alkalosis. The data suggest that in various acid-base states the rate of renal gluconeogenesis is linearly correlated with malate efflux from the mitochondria. In renal tissue, inhibition occurs at one site of the TCA cycle there is an augmentation of fluxes through pathways beyond that site in order to maintain the respiratory process and the redox state in the mitochondria.

Acid-Base Imbalance↗
PubMed1990

Carbon flux through tricarboxylic acid cycle in rat renal tubules.

Our aim was to delineate the effect(s) of chronic metabolic acidosis on renal TCA-cycle metabolism. Renal tubules isolated from control and chronically acidotic rats were incubated at pH 7.4 with either 2 mM [2,3-13C]pyruvate or [2-13C]acetate. GC-MS and/or 13C-NMR were utilized to monitor the flux of 13C through pyruvate dehydrogenase, pyruvate carboxylase and the TCA-cycle. With either, precursor acidosis was associated with significantly decreased formation of 13C-labelled citrate, malate, aspartate and alanine and increased formation of glucose, lactate and acetyl-CoA as compared with the control. The results indicate that adaptation of renal metabolism to chronic metabolic acidosis is associated with diminished flux through citrate synthetase and concomitantly increased flux through pyruvate carboxylase. The data suggest that depletion of TCA-cycle intermediates and enhanced ammoniagenesis in the kidney of chronically acidotic rats may be regulated at the site of mitochondrial citrate-condensing enzyme.

Acidosis↗
PubMed1990

Precursors of glutamic acid nitrogen in primary neuronal cultures: studies with 15N.

We utilized gas chromatography-mass spectrometry to study the transfer of 15N from [2-15N]glutamine, [15N]leucine, [15N]alanine, or 15NH4Cl to [15N]glutamate and [15N]aspartate in cultured cerebrocortical GABA-ergic neurons from the mouse. Initial rates of 15N appearance (atom % excess) were somewhat higher with 2mM [2-15N]glutamine as a precursor than with 1mM [15N]leucine or 1mM [15N]alanine, but initial net formation (nmol [15N]glutamate/mg protein.min-1) was roughly comparable with all precursors. At steady-state 15N labeling was about two times greater with 2mM [2-15N]glutamine as precursor. The subsequent transfer of 15N from glutamate to aspartate was extremely rapid, the labelling pattern of these two amino acid pools being virtually indistinguishable. We observed little reductive amination of 2-oxo-glutarate to yield [15N]glutamate in the presence of 0.3mM 15NH4Cl. Reductive amination through glutamate dehydrogenase was much more prominent at a concentration of 3.0mM 15NH4Cl. Glutamate formation via reductive amination was unaffected by inclusion of 1mM 2-oxo-glutarate in the incubation medium. These results indicate that glutamate synthesis in cultured GABA-ergic neurons is derived not only from the glutaminase reaction, but also from transamination reactions in which both leucine and alanine are efficient N donors. Reductive amination of 2-oxo-glutarate in the glutamate dehydrogenase pathway plays a relatively minor role at lower concentrations of extracellular ammonia but becomes quite active at 3mM ammonia.

Alanine↗
PubMed1990

Neuronal glutamine utilization: glutamine/glutamate homeostasis in synaptosomes.

The synaptosomal metabolism of glutamine was studied under in vitro conditions that simulate depolarization in vivo. With [2-15N]glutamine as precursor, the [glutamine]i was diminished in the presence of veratridine or 50 mM KCl, but the total amounts of [15N]glutamate and [15N]aspartate formed were either equal to those of control incubations (veratridine) or higher (50 mM [KCl]). This suggests that depolarization decreases glutamine uptake and independently augments glutaminase activity. Omission of sodium from the medium was associated with low internal levels of glutamine which indicates that influx occurs as a charged Na(+)-amino acid complex. It is postulated that a reduction in membrane potential and a collapse of the Na+ gradient decrease the driving forces for glutamine accumulation and thus inhibit its uptake and enhance its release under depolarizing conditions. Inorganic phosphate stimulated glutaminase activity, particularly in the presence of calcium. At 2 mM or lower [phosphate] in the medium, calcium inhibited glutamine utilization and the production of glutamate, aspartate, and ammonia from glutamine. At a high (10 mM) medium [phosphate], calcium stimulated glutamine catabolism. It is suggested that a veratridine-induced increase in intrasynaptosomal inorganic phosphate is responsible for the enhancement of flux through glutaminase; calcium affects glutaminase indirectly by modulating the level of free intramitochondrial [phosphate]. Because phosphate also lowers the Km of glutaminase for glutamine, augmentation of the amino acid breakdown may occur even when depolarization lowers [glutamine]i. Reducing the intrasynaptosomal glutamate to 26 nmol/mg of protein had little effect on glutamine catabolism, but raising the pH to 7.9 markedly increased formation of glutamate and aspartate. It is concluded that phosphate and H+ are the major physiologic regulators of glutaminase activity.

Animals↗
PubMed1990

Glutathione turnover in cultured astrocytes: studies with [15N]glutamate.

The incorporation of [15N]glutamic acid into glutathione was studied in primary cultures of astrocytes. Turnover of the intracellular glutathione pool was rapid, attaining a steady state value of 30.0 atom% excess in 180 min. The intracellular glutathione concentration was high (20-40 nmol/mg protein) and the tripeptide was released rapidly into the incubation medium. Although labeling of glutathione (atom% excess) with [15N]glutamate occurred rapidly, little accumulation of 15N in glutathione was noted during the incubation compared with 15N in aspartate, glutamine, and alanine. Glutathione turnover was stimulated by incubating the astrocytes with diethylmaleate, an electrophile that caused a partial depletion of the glutathione pool(s). Diethylmaleate treatment also was associated with significant reductions of intraastrocytic glutamate, glycine, and cysteine, i.e., the constituents of glutathione. Glutathione synthesis could be stimulated by supplementing the steady-state incubation medium with 0.05 mM L-cysteine, such treatment again partially depleting intraastrocytic glutamate and causing significant reductions of 15N labeling of both alanine and glutamine, suggesting that glutamate had been diverted from the synthesis of these amino acids and toward the formation of glutathione. The current study underscores both the intensity of glutathione turnover in astrocytes and the relationship of this turnover to the metabolism of glutamate and other amino acids.

Amino Acids↗
PubMed1990

Ammonia metabolism in cultured renal cells.

Many important aspects of the mechanism(s) abetting renal ammonia metabolism in man have remained unresolved. This review will summarize the advantages of cell culture and the stable isotope 15N techniques for the investigation of the biochemical mechanism(s) regulating renal ammoniagenesis. The application of these techniques for the study of renal ammonia metabolism has demonstrated a broad metabolic and biochemical similarity between intact kidney cells and those in culture. Renal cells in culture may provide a useful model for scrutinizing various aspects of renal ammoniagenesis.

Ammonia↗
PubMed1989

Effect of 5-amino-4-imidazolecarboxamide riboside (AICA-riboside) on the purine nucleotide synthesis and growth of rat kidney cells in culture: study with [15N]aspartate.

The present investigation evaluates the effect of AICA-Riboside on the synthesis of purine nucleotides and the growth of normal rat kidney cells in culture. Experiments in the presence and absence of various concentrations of AICA-Riboside were conducted with Dulbecco's Modified Eagle's Medium supplemented with either 1 mM [15N]aspartate or [14N]aspartate. Addition of 50 microM AICA-Riboside to the incubation medium significantly stimulated intracellular adenine nucleotide concentrations following incubation for 48 hours. This stimulation was associated with augmented cell growth and DNA concentration. In contrast, with concentrations above 100 microM of AICA-Riboside in the incubation medium, there was a remarkable inhibition of cell growth and a significant depletion of intracellular pools of adenine nucleotides and DNA. Experiments with [15N]aspartate showed that the initial rate (0-24 hours) of [6-15NH2]adenine nucleotide formation from 1 mM [15N]aspartate was 38.8 +/- 9.6, 67.9 +/- 12.5, and 20.1 +/- 3.8 pmol h-1/10(6) cells in the presence of 0 (control), 50 microM and 500 microM AICA-Riboside, respectively. These observations indicate that the main effect of AICA-Riboside is on the formation of AMP from aspartate and IMP via the sequential action of adenylosuccinate synthetase and adenylosuccinate lyase. The current studies suggest that AICA-Riboside could be used as a factor mediating renal cell mitosis in culture. AICA-Riboside has a biphasic effect on the growth of renal epithelial cells in culture and on their intracellular purine nucleotides and DNA concentration.

Adenine Nucleotides↗