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PubMed1987

Responses to excess dietary magnesium as affected by experimental Eimeria acervulina infection or by dietary ammonium chloride ingestion in the chick.

Three experiments were conducted to investigate the effect of experimental Eimeria acervulina infection on excess Mg ingestion in the chick and to investigate the effect of NH4Cl addition to the diet on the coccidiosis X Mg interaction. Two Mg sources were evaluated, MgO and MgSO4 X 7H2O. Gain, efficiency of feed utilization, bone ash percent (BAP), bone Ca and duodenal pH were lower in coccidiosis-infected chicks than in uninfected chicks. However, bone P and bone Mg levels were higher as a result of the coccidial infection. Bone Mg levels were higher and bone Ca levels and BAP were lower in chicks fed excess dietary Mg, either as the oxide or sulfate forms. Gain and feed efficiency of chicks fed excess Mg, as MgO but not as MgSO4 X 7H2O, were lower than in chicks fed the basal level of Mg. Coccidiosis X Mg interactions were observed in bone Mg and bone Ca concentration data; bone Mg uptake was greater when high dietary Mg and the coccidial infection were in combination. In some instances, a similar interactive effect was observed in bone Ca concentration data; bone Ca loss tended to be greater as a result of the combination of high dietary Mg and the coccidial infection.

Ammonium Chloride↗
PubMed1983

Isolation of chloroquine-resistant Chinese hamster V79 cell variants that are also resistant to ammonium chloride.

Chloroquine-resistant (CQr) clones (CQ-21 and CQ-22) have been isolated from mutagenized hamster lung V79 cells by exposing the cells to a high dose of chloroquine. CQ-21 and CQ-22 showed about 3-fold higher resistance to chloroquine than the parental V79 cells, and they showed specific cross-resistance to another amine, NH4Cl, which is also concentrated in lysosomes. CQr clone showed no cross-resistance to other unrelated agents. Chloroquine-induced inhibition of [125I]ricin internalization was observed in both cell lines at neutral pH, but the inhibition of uptake was less in the variant. Also, the degradation of endogenous protein was slowed in the mutant; further, treatment of cells with 30 micrograms/ml of chloroquine inhibited the degradation of endogenous proteins in the parental V79, but not in CQ-22 cells. Similar levels of acid phosphatase, beta-glucuronidase and cathepsin D were observed in V79 and CQ-22 cells, but the level of cathepsin B was lower in the mutant. Electron microscopy showed an increased number of electron-dense bodies, possibly autophagosomes/lysosomes, in the mutant cells grown for 4 days with 5 micrograms/ml of chloroquine. Similar aberrant structures were observed in the parental V79 cells treated for only 3 h with 5 micrograms/ml of chloroquine.

Ammonium Chloride↗
PubMed1974

Mechanisms for the formation of alanine and aspartate on rat liver in vivo after administration of ammonium chloride.

1. The time-course of the changes in the concentrations of hepatic metabolites in response to a non-toxic load of NH(4)Cl were measured in fed and starved rats. 2. There was a rapid increase (after 2min) in [alanine] and [aspartate] which remained high for 10-15min; the absolute increase in [alanine] was smaller in starved rats. 3. These changes were accompanied by a decrease in [oxoglutarate] and in the [3-hydroxybutyrate]/[acetoacetate] ratio. 4. Prior administration of l-arginine to fed rats resulted in smaller increases in [alanine] and [aspartate] after the ammonia load. This is presumably due to stimulation of the urea cycle. 5. Increased formation of alanine in starved rats occurred after prior administration of dihydroxyacetone to increase the availability of pyruvate. 6. Administration of l-cycloserine, an inhibitor of glutamate-alanine aminotransferase, completely prevented the increase in [alanine] after the ammonia load; in this case the absolute increase in [aspartate] was higher. 7. [Oxoglutarate], [citrate] and [isocitrate] at 25min after the ammonia load were higher than the initial concentrations, but returned to normal by 50min. It is suggested that this ;overshoot' may be due to temporary compartmentation of oxoglutarate. 8. The mechanisms and physiological significance of alanine and aspartate formation in these experiments are discussed.

Alanine↗
PubMed1981

Glucagon degradation in isolated rat hepatocytes: effect of ammonium chloride and chloroquine.

It has recently been shown that, when [125I]glucagon is incubated with isolated rat hepatocytes at 37 degrees, the radiolabeled material is progressively internalized by the cell and is found to associate preferentially with lysosome-like structures. To assess the role of this process in the degradation of the hormone, the degradation of [125I]glucagon by isolated rat hepatocytes was examined both in incubation media and in cell extracts, after exposure of the radiolabelled hormone to hepatocytes in the absence and in the presence of lysosomotropic agents NH4Cl (8 mmoles/l) or chloroquine (10 micromoles/l); bacitracin (0.8 mg/ml, i.e. 0.6 mmoles/l) was present in all experimental conditions to minimize extracellular degradation. Neither NH4Cl nor chloroquine altered the time course and steady-state binding of [125I]glucagon, or the degradation of the hormone in incubation media. However, both agents partially inhibited the degradation of cell-associated [125I]glucagon in steady-state conditions. In dissociation experiments, NH4Cl, and even more so chloroquine, decreased the rate and the extent of release of radiolabelled material from the cells. Moreover, after 60 min dissociation, the presence of either agent resulted in less degradation of both cell-associated [125I]glucagon and that released into the medium. These results suggest that lysosomes are involved in the intracellular degradation of glucagon.

Ammonium Chloride↗
PubMed1978

The effects of ammonium chloride and bicarbonate on the activity of glutaminase in isolated liver mitochondria.

1. Glutamine hydrolysis in liver mitochondria was studied by measuring the production of glutamate under conditions where this compound could not be further metabolized. 2. Glutaminase activity in intact mitochondria was very low in the absence of activators. 3. Glutamine hydrolysis was markedly stimulated by NH4Cl and also by HCO3- ions. 4. The stimulation by each of these compounds was much decreased if the mitochondria were uncoupled. 5. Maximum rates of glutamine hydrolysis required the addition of phosphate. A correlation was observed between the activity of glutaminase in the presence of NH4Cl plus HCO3- and the intramitochondrial content of ATP. 6. In disrupted mitochondria, NH4Cl stimulated glutaminase to a much smaller extent than in intact mitochondria. The NH4Cl stimulation in disrupted mitochondria was much increased by the addition of ATP. KHCO3 also stimulated glutaminase activity in disrupted mitochondria, and ATP increased the magnitude of this stimulation. 7. It was concluded that maximum rates of glutaminase activity in liver mitochondria require the presence of phosphate, ATP and either HCO3- or NH4+. A comparison of the results obtained on intact and broken mitochondria indicates that these effectors have a direct effect on the glutaminase enzyme system rather than an indirect effect mediated by changes in transmembrane ion gradients or in the concentrations of intramitochondrial metabolites.

Adenosine Triphosphate↗
PubMed1988

Stimulation of uracil nucleotide synthesis in mouse liver, intestine and kidney by ammonium chloride infusion.

De novo pyrimidine synthesis was studied in mouse liver, intestine, and kidney by intraperitoneal infusion of 15NH4Cl and analysis of 15N incorporation into uracil nucleotide pools. When the dose of a 1-h infusion of 15NH4Cl was increased from 50 mumol to 250 mumol the fraction of the total uracil nucleotide pool formed by de novo synthesis increased 4.0-fold in liver to 8.4% and 2.3-fold in intestine to 13.7%. The increase in intestine was independent of the increase in liver as evidenced by the lack of correlation between the increase observed in the intestine and liver of the same animal and the different distributions of label in the uracil ring nitrogens. A 2.4-fold increase in newly formed uracil nucleotides was observed in kidney when the infusion dose was raised from 150 mumol to 250 mumol. The increase in kidney was correlated with the increase in liver in the same animal and the distribution of label in the uracil ring nitrogens was similar to the distribution in liver. These results suggest that the increase in newly formed uracil nucleotides in intestine is due to increased de novo synthesis of pyrimidines in the intestine, while the increase in the kidney is due to increased salvage synthesis of uracil nucleotides from uridine synthesized in the liver and output to the circulation.

Algorithms↗
PubMed1994

Changes in mRNAs for enzymes of glutamine metabolism in kidney and liver during ammonium chloride acidosis.

Changes in protein and mRNAs for enzymes of glutamine metabolism were determined in rat kidney cortex at different times after induction of NH4Cl acidosis. After NH4Cl, phosphoenolpyruvate carboxykinase (PEPCK) mRNA increased 16-fold by 10 h (P < 0.05) and then returned to control levels by 30 h. In situ hybridization (ISH) showed that PEPCK mRNA was confined to medullary rays; after NH4Cl, expression of PEPCK expanded throughout the cortex, reaching a maximal intensity at 10 h. Phosphate-dependent glutaminase (PDG) and glutamate dehydrogenase (GDH) mRNAs increased 8- and 2.6-fold, respectively (both P < 0.05), by 10 h before decreasing; the increased expression was confirmed by ISH. Immunohistochemistry showed that increased PEPCK, PDG, and GDH protein occurred at variable times after the rise in mRNAs. The increase was confined to proximal tubules and was sustained, a finding noted also by Western blot analysis. In contrast, glutamine synthase protein and mRNA, confined to deep cortex and outer medullar, did not change after NH4Cl. These studies reveal striking changes in PEPCK and PDG mRNAs in rat renal cortex during acidosis. The ISH pattern suggested that increased amounts of PEPCK were synthesized in recruited cells which contained little enzyme under physiological conditions. mRNA levels for PEPCK, PDG, and GDH peaked at 10 h before returning to control levels. Despite the decrease in mRNAs, a sustained increase in proteins was noted.

Acidosis↗
PubMed1999

[Compensatory changes in the acid-base balance under the influence of excess ammonium chloride, hypodynamia and stress].

Two variants of alternative integrative compensatory mechanisms of metabolic reactions in organism developing at the compensated shifts of acid-base balance under the influence of different risk factors have been discovered by the authors. Compensated metabolic acidosis appears with the excess of salt ammonia in the animals ration, at the immobilization stress, hypodynamia, deafferentation and surgical stress. The start reaction of acidosis is lipolysis activation and nonacidified products accumulation at the reactions of tricarboxylic acid cycle are (TAC) inhibited. The compensatory mechanism directed to bind hydrogen ions and prevent pH shifts is activity of glyconeogenesis reactions, transamination, increase the contents ammonia, as well as by increases of restored combinations. Carbohydrates excess in the ration, emotional stress (anxiety expectation) lead to the metabolic alkalosis development at which low hydrogen ion formation and their rapid use in the activated process of peroxide lipids oxidation is compensated with the increase of organic acids formation in glycolysis and TAC as well as by the increase of oxidation properties in tissues. Besides adaptive physiological meaning, the described mechanisms may be the reason for a number of pathological state appearance. The discovery in population and prevention of endogenic risk factors prevention is principle new basis of modern integrated system of human and animals common diseases prevention.

Acid-Base Equilibrium↗
PubMed1990

Ammonium chloride causes reversible inhibition of low density lipoprotein receptor recycling and accelerates receptor degradation.

The effects of the acidotropic agent, NH4Cl, on the recycling and turnover of low density lipoprotein (LDL) receptors were analyzed in human skin fibroblasts using ligand binding assays, [35S]methionine pulse-chase experiments, and electron microscopy. NH4Cl did not prevent receptor internalization but caused a marked redistribution of LDL receptors to intracellular sites (endosomes) that was completely dependent on the presence of apolipoprotein-B- or -E-containing ligands. Maximal inhibition of recycling was observed at LDL concentrations that only partially saturated receptors, suggesting that the receptors function as oligomers. In contrast, full receptor occupancy by the multivalent, apolipoprotein-E-containing beta-very low density lipoprotein was required for the same effect. The intracellular accumulation was reversible and the majority of receptors returned to the cell surface when NH4Cl was removed after short treatments. The rate of degradation of LDL receptors was greatly accelerated in the presence of NH4Cl and ligand, with a t1/2 of about 2 h (approximately 6 times faster than receptor degradation in the absence of NH4Cl). Neither the redistribution nor the accelerated loss of immunoprecipitable LDL receptors was observed in an LDL receptor internalization-defective mutant cell line. We conclude that NH4Cl inhibited the recycling specifically of occupied receptors, thereby accelerating their degradation, probably in endosomes.

Ammonium Chloride↗
PubMed1986

Ammonium chloride induced acidosis and aldosterone secretion in the goat.

Responses to 30-min intraduodenal infusion of NH4Cl (total amount 75 mmol) were studied in conscious goats. The infusion caused an immediate, transient rise in plasma aldosterone concentration (PA) from a mean of 78 to 221 pmo l-1. As expected, the NH4Cl administration also induced metabolic acidosis, initially subjected to partial respiratory compensation. The acidosis did not become fully developed until 1 h after cessation of the infusion, when PA had almost returned to its initial level. Renal compensation of the acidosis was shown by acidification of the urine and reduced Na excretion being most pronounced 1-2 h post-infusion. During the infusion blood haemoglobin concentration and the haematocrit increased by 25 and 13%, respectively, without simultaneous increase in plasma protein concentration and with persisting ear vasodilatation, indicating a mobilization of stored erythrocytes in the absence of a general increase in sympathetic tone. The results suggest that the reduction of blood pH is not the cause of the increase in PA occurring in association with NH4Cl-induced metabolic acidosis, but leave open the possibility that this increase may be due to some centrally mediated or direct adrenal influence of NH+4. As regards the apparent NH4Cl-induced mobilization of stored erythrocytes, it is suggested that such a response may play a role in the defence against acidosis by increasing the buffering capacity of the circulating blood.

Acid-Base Equilibrium↗
PubMed1983

Glycosylation of proteins from sugar nucleotides by whole cells. Effect of ammonium chloride treatment on mouse thymocytes.

When thymocytes are treated with iso-osmotic NH4Cl, the sugar incorporation into endogenous acceptors from labelled sugar nucleotides is largely increased compared with that in control thymocytes. This effect was obtained with labelled GDP-mannose, UDP-galactose and CMP-N-acetylneuraminic acid. The stimulation observed with NH4Cl-treated thymocytes does not involve the glycosylation of exogenous acceptors, and it was proved that the NH4Cl treatment (1) does not stimulate glycosyltransferase activities themselves, (2) does not lead to the release of soluble glycosyltransferases as the result of an extensive lysis of the thymocytes and (3) does not cause the emergence of glycosyltransferases at the cell surface. In fact, electron-microscopy observations showed that, although marked changes had occurred in the cytoplasm, the plasma membrane is sufficiently maintained to allow the cell to keep roughly its original shape and to retain the intracellular vesicles. We thus demonstrate that this stimulation is due to an enhancement of the entry of sugar nucleotides into the cell. As demonstrated by the inclusion of Trypan Blue within the cells, and the non-stimulation of glycosylation of exogenous large-molecular-mass acceptors, the effect of NH4Cl seems to be limited to the penetration of small-molecular-sized compounds through the plasma membrane. Thus NH4Cl treatment allows the labelled sugar nucleotides to penetrate the cell and to behave as the cellular pool to be utilized for glycosylation by intracellular vesicles.

Ammonium Chloride↗
PubMed1976

Inhibition by ammonium chloride of the oxygen yield of photosynthesis.

Flash O2 yield experiments are described in spinach chloroplasts and Chlorella after addition of NH4Cl. (1) The damping of the sequence is increased by NH4Cl. (2) The turnover times are accelerated but the reaction during which O2 is released (S3bv leads to S4 leads to S0) is slowed. (3) We observed between the end of the turnover kinetic and the beginning of deactivation a latency time tl during which the S2 and S3 states are perfectly stable. In the presence of NH4Cl, this latency time for S2 is shortened, diminishing from 1 s to less than 12 ms; whereas it is lengthened for S3 (up to 4 s, 5 s). (4) After this latency time, two phases are clearly distinguished in the S2 deactivation: the beginning of the deactivation is abrupt, varying like the square root of the time, i.e. as is characteristic of a diffusive process. During the second phase, S2 is stabilized. Our experiment shows that S2 deactivation is monitored by the release of some product F after the latency time from one particular locus, so that nearby Photosystem II reaction centers are rapidly deactivated by diffusion of the product, whereas centers far from this locus are very slowly deactivated. These results are qualitatively complementary to the luminescence experiments of Velthuys (Biochim. Biophys, Acta (1975) 396, 392-401) except for the latency time which is invisible in the Velthuys results. We propose a modified model in which the binding of NH3 on states S2 and S3 occurs during deactivation.

Ammonium Chloride↗
PubMed2000

Bone, blood and faecal response to an acidogenic lick for range cattle using different concentrations of ammonium chloride.

Thirty Brahman-Angus cross heifers at breeding age on extensive grazing were used to test the effectiveness of NH4Cl as an acidogenic agent at 15,18, 21 and 26 % of a dicalcium phosphate lick (A+), compared to a lick of 5 parts dicalcium phosphate and 3 parts salt (A-). Blood and faecal phosphorus (P), faecal calcium (Ca) and faecal magnesium (Mg) were significantly (P<0.05) higher in A+ compared to A-animals at different stages of the experiment. Bone P did not increase in response to NH4Cl but bone Ca was significantly (P<0.05) higher in A+ animals offered 18% NH4Cl and significantly (P<0.05) lower at 15 and 26%. Bone Mg in A+ animals was significantly (P<0.05) higher at 15 and 18% NH4Cl and lower at 26% NH4Cl compared to A- animals. Percentage ash in bone increased linearly from 62.5 to 64.9% in A+ animals as NH4Cl was increased in the lick from 15 to 21% and then decreased to 63.3% but was significantly (P<0.05) greater than the percentage ash in A-animals when the NH4Cl was increased to 26%. Bone mineral status was only marginally improved by adding NH4Cl to the lick in this study but blood P was significantly (P<0.05) improved in A+ compared to A- animals when the lick contained 15, 21 and 26% NH4Cl. Based on bone mineral results reported here, it is recommended that, when NH4Cl is used as an acidogenic agent in licks for range cattle, the amount in the lick should not exceed 21%.

Ammonium Chloride↗
PubMed1985

Endocytosis of an antibody ricin A-chain conjugate (immuno-A-toxin) adsorbed on colloidal gold. Effects of ammonium chloride and monensin.

An immunotoxin (IT) formed by a specific antibody coupled to the ricin A chain was adsorbed on colloidal gold particles (IT-Au). Binding and internalization of IT-Au in human lymphoblastic CEM cells were studied using electron microscopy. IT-Au showed specific cytotoxic activity toward the target cells. After 1 h at 4 degrees C, IT-Au were linked diffusely to the plasma membrane with 45% of the particles regrouped in clusters. Upon transfer to 37 degrees C, the particles carrying the ligand were regrouped more frequently and internalized into the cell by endocytosis through smooth microinvaginations or coated pits of the plasma membrane. After 15 min, IT-Au was observed in endocytic vacuoles, or receptosomes, in tubular structure near the Golgi apparatus and in lysosomes. Entry of IT-Au into lysosomes was rapid (around 50% of intracellular IT-Au particles after 30 min). NH4Cl or monensin, well-known potentiators of immunotoxin activity, when present in incubation medium, altered neither the processes nor the rate of IT-Au endocytosis. In the presence of either of these substances, IT-Au accumulated in the normal or often enlarged endocytic vacuoles, and entry into the lysosomes was slowed down (50% of particles after 2 h 15 min). We conclude that this intense slowing-down in the speed of IT-Au transportation into lysosomes and the functional modifications of these organelles help to explain the increased efficacy of immunotoxins in the presence of potentiators.

Adsorption↗
PubMed1994

Glutamine synthesis from glucose and ammonium chloride by guinea-pig kidney tubules.

1. At a physiological concentration (5 mM), glucose was found to be metabolized by isolated kidney cortex tubules prepared from fed guinea pigs. 2. The release of 14CO2 from [U-14C]glucose indicated that oxidation of the glucose carbon skeleton represented about 50% of the glucose removed; significant amounts of lactate and glutamine also accumulated. 3. Addition of 0.1-10 mM NH4Cl led to a dose-dependent stimulation of glucose metabolism which was accompanied by a large increase in lactate and glutamine accumulation and, to a lesser extent, in glucose oxidation. 4. Comparison of the release of 14CO2 from [1-14C]- and [6-14C]glucose indicates that, in both the absence and the presence of NH4Cl, the pentose phosphate shunt was only a minor pathway of glucose metabolism. 5. The central role of pyruvate carboxylase in the conversion of glucose carbon into glutamine carbon was demonstrated by using a bicarbonate-free medium and measuring the fixation of 14CO2 from [14C]bicarbonate, which was recovered mostly at C-1 of glutamine plus glutamate. 6. The NH4Cl-induced stimulation of glucose removal was secondary not only to increased glutamine synthesis, as shown by the effect of methionine sulphoximine, an inhibitor of glutamine synthetase, but also to the stimulation of phosphofructokinase activity by NH4Cl. 7. Renal arterio-venous difference measurements revealed that, in vivo, the guinea-pig kidney removed glucose from the circulating blood, which suggests that glucose carbon may contribute to the carbon skeleton of the glutamine released by this organ.

Ammonium Chloride↗
PubMed1990

Effect of ammonium-chloride-induced metabolic acidosis on renal electrolyte handling in human neonates.

The present study was undertaken to determine the relative contribution of altered glomerular and tubular functions to the metabolic-acidosis-induced increase of renal electrolyte excretion in healthy preterm and full-term neonates and in older infants. Studies were performed in 10 premature infants (mean birth weight 1618 g, gestational age 30.8 weeks) weekly for 6 consecutive weeks, in 11 full-term neonates (mean birth weight 3085 g, gestational age 38.6 weeks) on the 7th day of life and in 25 older control infants (mean age 6.5 months, body weight 6802 g), before and after NH4Cl loading. Blood acid-base parameters, plasma and urine electrolyte and creatinine concentrations were measured, endogenous creatinine clearance and fractional electrolyte excretion (FE) calculated. It was demonstrated that the significant reduction in blood pH and total CO2 content induced by NH4Cl administration was associated with significant increases in glomerular filtration rate (GFR), urine flow rate, FENa and FECl, in each group studied, irrespective of maturity, postnatal age or pre load values. FEK also tended to increase, but the change reached statistical significance only in older infants and in premature babies during the 1st, 2nd and 5th week of post-natal life. FECa and FEPO4 increased slightly in preterm and full-term newborns and became significant in older infants. Prior to NH4Cl administration, FECa correlated positively with FENa in each group. NH4Cl metabolic acidosis, however, dissociated FECa from FENa in the full-term newborns and older infants but not in the preterm neonates.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid-Base Equilibrium↗
PubMed1985

Ammonium chloride, methylamine and chloroquine reversibly inhibit antibody secretion by plasma cells.

The effects of the lysosomotropic weak bases, NH4Cl, methylamine and chloroquine, on the secretory process of antibody-synthesizing cells were studied. Popliteal lymph node cells taken from rats immunized against horseradish peroxidase (HRP) were incubated with the lysosomotropic agents. The rate of secretion of anti-HRP antibodies was measured using an indirect enzyme-linked immunosorbent assay. These agents induced an inhibition of antibody release within 5 min, and for all four concentrations tested, maximal inhibition was reached after 15 min. A 50% inhibition was obtained with 20 mM NH4Cl, 21.7 mM methylamine and 8.8 X 10(-4) M chloroquine. This effect was rapidly and entirely reversible, regardless of the weak base used, and it increased as the pH of the extracellular media was raised. Under these conditions, intracellular ATP contents remained normal, and protein synthesis did not undergo marked changes except with chloroquine. Inhibition of secretion was accompanied by an intracellular accumulation of antibodies which was equal to the degree of inhibition of antibody release. Immunocytochemical studies of the weak base-treated cells performed by light and electron microscopy showed that this accumulation probably occurred within certain dilated Golgi saccules. In addition, reduced incorporation of fucose into immunoglobulins as well as partial inhibition of the secretion of fucosylated immunoglobulins were observed in the presence of weak bases. These results are consistent with the hypothesis that weak bases inhibit antibody secretion by acting within saccules of the Golgi apparatus. These saccules could maintain an acidic pH important for the migration and/or sorting of immunoglobulins.

Adenosine Triphosphate↗
PubMed2003

Substrate inhibition of Lactococcus lactis cytidine 5'-triphosphate synthase by ammonium chloride is enhanced by salt-dependent tetramer dissociation.

Cytidine 5(')-triphosphate (CTP) synthase (EC 6.4.3.2) catalyzes the transfer of an amino group to the 4 position of uridine 5(')-triphosphate (UTP) to yield CTP. The reaction proceeds by activation of the base moiety of UTP by adenosine 5(')-triphosphate (ATP)-dependent phosphorylation. The activated intermediate reacts with NH(3) in the solution or is obtained by hydrolysis of glutamine. The Lactococcus lactis CTP synthase shows significant differences from the enzymes from Escherichia coli, yeast, and mammals. One is the apparent stability of the L. lactis CTP synthase tetramer in the absence of the nucleotides ATP and UTP. This condition causes the E. coli, yeast, and mammal enzymes to dissociate into dimers. However, the L. lactis CTP synthase shows substrate inhibition by NH(4)Cl that coincides with the range of NH(4)Cl concentrations that apparently dissociates tetrameric enzyme into dimers. Even though regular substrate inhibition was observed with NH(4)Cl when the ionic strength was held constant, a significant part of the inhibition could be shown to be due to the increase in ionic strength with increasing substrate concentration. Since the substrate inhibition by NH(4)Cl was relieved by increasing the equimolar ATP and UTP concentrations, it appeared that the substrate nucleotides stabilized the tetramer in a manner similar to that found in the absence of salt for other CTP synthases. In contrast to the suggested hydrophobic nature of the tetramer interactions in E. coli CTP synthase, the dissociation of the L. lactis CTP synthase tetramer in response to an increase in ionic strength suggests that the tetramer is stabilized by ionic interactions.

Adenosine Triphosphate↗