Role of hippurate in acidosis induced adaptation in renal gamma-glutamyltransferase

Metabolic acidosis results in an adaptation in renal γ-glutamyltransferase (γ-GT) and a doubling of hippurate excretion. The greater rate of γ-glutamohydroxamate, γ-GHA, formation from L-glutamine, but not from glutathione, by acidotic kidney homogenates suggest an increased γ-glutamyl-enzyme complex formation and a preference for glutamine as the γ-glutamyl donor in acidosis. Hippurate added $\text{in}$$\text{vitro}$ to cortical homogenates or microsomes mimics the affect of acidosis upon γ-GHA formation from glutamine. Acid extracts of urine stimulated ammonia formation from glutamine using cortical microsomes in agreement with the measured hippurate levels. Administering an exogenous hippurate load to fasting nonacidotic rats doubled ammonia excretion and the rate of γ-GHA formation by cortical homogenates. These results are consistent with the acidosis induced adaptation in renal γ-GT governed by hippurate.     

Evidence for lumenal and antilumenal localization of gamma-glutamyltranspeptidase in rat kidney

Gamma-Glutamyl-p-nitroanilide (γ-GpNA) utilization was studied using the isolated rat kidney perfused with 1.5 mM γ-glutamyl-p-nitroanilide and 8 mM glycylglycine (glygly). In the absence of glygly, autotransfer products, γ-glu-γ-glu-p-NA appeared in the perfusate while glutamate, the hydrolytic product, appeats in the urine. In the presence of glygly, p-nitroaniline (p-NA) formation was stimulated 3-fold with the appearance of γ-gluglygly as the major product in both the perfusate and urine. Under conditions of single pass perfusion, 89 percent of the γ-glutamyl-p-nitroanilide utilization occurs on the antilumenal border and only 11 percent on the lumenal border; ureter ligation reduced glomerular filtration 90 percent but does not significantly reduce utilization. However, reducing the perfusate flow rate of the antilumenal side to that of the lumenal results in a utilization rate which is approximately one-third that of the lumenal, suggesting that the lumenal border enzyme is at least 3 times in excess of the antilumenal border enzyme.     

Hydrolysis and transfer reactions catalyzed by gamma-glutamyl transpeptidase; evidence for separate substrate sites and for high affinity of L-cystine.

γ-Glutamyl transpeptidase was studied with L- and D-γ-glutamyl-p-nitroanilide as γ-glutamyl donors. No autotranspeptidation occurred with the D-γ-glutamyl donor or when the L-γ-glutamyl donor was used at concentrations lower than 10 μM. The K_m values for hydrolysis were 5 and 31 μM for the L- and D-γ-glutamyl donors, respectively; the corresponding V_max values were identical. The γ-glutamyl donor site of the enzyme thus exhibits low stereospecificity (but high affinity), while the acceptor site exhibits absolute L-specificity. The K_m value for L-cystine as acceptor is very low (30 μM); the same value was obtained with L- and D-γ-glutamyl donors. The data are consistent with a ping pong mechanism and the existence of separate donor and acceptor enzyme sites. The present findings thus extend the usefulness of γ-glutamyl-p-nitro-anilide as a substrate in probing the catalytic behavior of this enzyme.     

Cutaneous ion exchange,and renal and extrarenal partitioning of acid and ammonia excretion in the larval tiger salamander,Ambystoma tigrinum,following ingestion of ammonium salts

Summary The skin/gills and the kidneys of aquatic amphibians are potential sites of acid-base regulation. The roles of these organs in acid-base balance were examined in larval Ambystoma tigrinum following gastric infusion of ammonium salts. A single dose of 1.75 mEq NH₄Cl·100 g^-1 produced a mixed acidosis by 1 h after gavage. By 8 h after ingestion, pH and HCO ₃ ^– had increased and PCO₂ had decreased as the animals recovered. A prolonged acidosis was developed in a second group by gavage of an initial dose (1.5 mEq·100 g^-1), followed by periodic maintenance doses (0.25 mEq·100 g^-1) to prolong the disturbance for 8 h. The magnitude of the acidosis during this period was similar to that seen at 1 h after ingestion in the time-course study. A third group of larvae were given NaCl as a control for salt loading, which induced a small but significant respiratory acidosis. Unidirectional fluxes of Na⁺ and Cl^- were examined during these serial ingestions. Salt loading inhibited the influx of the ingested ion. Na⁺ influx increased during the NH₄Cl-induced acidosis. A fourth group of larvae were used to partition acid and ammonia excretion between the skin and the kidneys. These animals were given (NH₄)₂SO₄ to allow re-examination of Cl^- flux rates under non-Cl^--loaded conditions. The ensuing acidosis had a reduced respiratory component and, therefore, pH did not decrease as much. Cl^- influx rates did decrease significantly under these conditions. In both control and acidotic conditions, the majority of the acid efflux was as ammonia and the skin was the primary site of acid excretion. However, both the skin and the kidneys increased total acid excretion, although the efflux across the skin showed a much greater increase. This suggests a primary role for the skin in acid-base regulation in aquatic amphibians.Abbreviations GFR glomerular filtration rate - PO₂ partial pressure of oxygen - PCO₂ partial pressure of carbon dioxide - SITS 4-acetamido-4-isothiocynanatostilbene-2,2-disulfonic acid - TA titratible acidity Present address: Department of Organismal Biology and Anatomy, University of Chicago, 1025 E. 57th St., Chicago, IL 60637, USA     

gamma-Glutamyl transpeptidase in Hydra.

γ-Glutamyl transpeptidase (EC 2.3.2.2) activity is described in the coelenterate, $\text{Hydra}$$\text{attenuata}$, using the substrate γ-glutamyl-p-nitroanilide. The properties of the γ-glutamyl donor required for binding to the transpeptidase were investigated by measuring the ability of GSH analogs to inhibit the release of p-nitroaniline. Whereas no binding was observed when the γ-glutamyl moiety was altered, analogs with substitution in the Cys residue were capable of binding to the enzyme. A specificity for the Gly residue was indicated because analogs containing Leu or Tyr in place of Gly exhibited decreased binding capacities for the hydra transpeptidase. A comparison of these data with those obtained using the same analogs in the GSH induced feeding response bioassay shows that γ-glutamyl transpeptidase activity and the GSH receptor for the hydra feeding response have different specificities.     

Acute and chronic acidosis influence on antioxidant equipment and transport proteins of rat jejunal enterocyte

Acidosis elicits the formation of oxidants and, in turn, ROS (reactive oxygen species)-induced intestinal diseases cause acidosis. This research investigated whether both acute and chronic acidosis influence the antioxidant enzymatic equipment of rat jejunocyte, including γ-GT activity, involved in GSH (glutathione) homoeostasis. Lipid peroxidation level and the expressions of (Na+, K+)-ATPase and GLUT2 were also investigated. The possible influence of acidosis on ROS action was tested. Isolated apical membranes, everted sac preparations and homogenates from acidotic rats were used. γ-GT activity is inhibited after incubation of isolated membranes at acidic pH, but using the whole intestinal tract this inhibition disappears, while SOD (superoxide dismutase) and GR (glutathione reductase) activities are enhanced. Also, in conditions of chronic acidosis, γ-GT activity is unaffected, but no variations of antioxidant activities are apparent. (Na+, K+)-ATPase expression increases, while GLUT2 decreases in acidotic animals. Lipid peroxidation level is unaffected by acidosis. H2O2 inhibits γ-GT activity only in isolated membranes; in the whole tissue, it enhances CAT (catalase) and SOD activities and reduces GLUT2 expression. The pattern of responses to oxidant agents is unaffected by acidosis. Although jejunum seems quite resistant to acidosis, results, suggesting specific responses to this condition, may direct further research on antioxidant supplementation.     

Enzymatic synthesis of theanine with Escherichia coli γ-glutamyltranspeptidase from a series of γ-glutamyl anilide substrate analogues

In order to investigate the catalytic mechanism of Escherichia coli γ-glutamyltranspeptidase, ten para- and meta-substituted γ-glutamyl anilides were chemically prepared and employed as substrates to synthesize L-theanine to assay the activity of γ-glutamyltranspeptidase. The reaction was optimized for γ-glutamyl-p-nitroanilide. Key factors such as substrate specificity, pH, temperature, and the substrate mole ratio were all investigated. Kinetic studies of the acyl transfer reaction were described and the Hammett plot was constructed. This study indicated that the ratelimiting acylation reaction of γ-glutamyltranspeptidase can apparently be accelerated by either the electron-withdrawing or electron-donating substituents of γ-glutamyl anilides. The reaction could be catalyzed by the general acid and carboxy of Asp-433 or phenolic hydroxyl Tyr-444 may be the acid by autodock simulation for all prepared γ-glutamyl anilides.     

Metabolism of glutamine and glutamic acid by isolated perfused kidneys of normal and acidotic rats

1. When isolated kidneys from fed rats were perfused with glutamine the rate of ammonia release at pH7.4 (110–360μmol/h per g dry wt.) was one to two times that of glutamine removal. Glucose formation from 5mm-glutamine was 16μmol/h per g. If kidneys were perfused with glutamine at pH7.1 (10–13mm-sodium bicarbonate) there was no increase in glutamine removal or in the formation of ammonia or glucose. 2. When isolated kidneys from fed rats were perfused with glutamate at pH7.4, glucose formation was 59μmol/h per g, glutamine formation was 182μmol/h per g and ammonia release was negligible. At pH7.1 glutamine synthesis was inhibited and formation of ammonia and glucose were increased. 3. In perfused kidneys from acidotic rats, which had received 1.5% (w/v) NH₄Cl to drink for 7–10 days, gluconeogenesis from glutamine was enhanced (101μmol/h per g). Glutamine removal and ammonia formation were also increased, compared with the rates in perfused kidney from normal rats. The extra glutamine consumed was equivalent to the extra glucose formed. 4. When the kidney from the 7–10-day-acidotic rat was perfused with glutamate gluconeogenesis was increased (113μmol/h per g). Synthesis of glutamine was decreased, and ammonia release was approximately equal to the rate of glutamate removal. 5. The time-course of these metabolic alterations was investigated after the rapid induction of acidosis by infusion of 0.25m-HCl into the right side of the heart. The increase in gluconeogenesis from glutamine developed gradually over several hours. When kidneys from 6h-acidotic rats were perfused with glutamate, formation of glucose and glutamine were both rapid. 6. In acidotic rat kidneys perfused with glutamine, tissue concentrations of glutamate and glucose 6-phosphate were increased compared with those in control perfused kidneys from non-acidotic rats. 7. The results are discussed in terms of control of the renal metabolism of glutamine. In particular, it is suggested that in acidotic rats glucose formation is the major fate of the carbon of the extra glutamine utilized by the kidney, and that inhibition of glutamine synthetase could contribute to the increase in intracellular ammonia concentration in the kidney.     

Identification of two mitochondrial GDP-binding sites in rat brown adipose tissue

Scatchard analysis of specific guanosine-diphosphate-([³H]GDP-) binding to rat brown-adipose-tissue mitochondria revealed two distinct binding sites with apparent dissociation constants (K_d) of approximately 0.05 and 2.0 μM. Binding to both sites was insensitive to atractyloside. Reducing the pH of the binding medium from 7.1 to 6.6 caused marked reductions in the K_d of both sites, but at pH 7.6, the dissociation constants were increased about 3-fold. Acute treatment of rats with noradrenaline, 1 h before sacrifice, increased the maximum number of binding sites (B_max, pmol/rng mitochondrial protein) of both sites and also increased the dissociation constants. The Bmax of the lower-affinity site was elevated in rats exposed to 5°C or fed a palatable cafeteria diet for 10 d, compared to control animals, with the greater changes occurring in the cold-adapted group. The high-affinity site was unaltered by cold adaptation or cafeteria feeding. These results indicate the presence of two distinct nucleotide-binding sites in brown-fat mitochondria, both of which may be involved in thermogenesis.     

Adaptation to respiratory acidosis in the turtle bladder

The effect of in vivo respiratory acidosis for 4 and 48 hr was examined in the turtle bladder by placing turtles in hypercapnic chambers. Blood pH was significantly lowered and pCO2 was significantly elevated over control values both 4 and 48 hr, while blood bicarbonate was only increased after 48 hr. In vitro rates for H+ secretion determined by the reverse short-circuit current were significantly greater in bladders from 48 hr of respiratory acidosis than those of controls (27.3 +/- 2.7 vs 20.6 +/- 1.7 microA, P less than 0.05). In vitro rates for HCO3- secretion determined by pH stat were not altered. Fluorescence microscopy was used to study cell morphology. The number of carbonic anhydrase cells (corrected for the total number of cells) as determined by four different fluorescence stains (6-carboxyfluorescein, rhodamine 123, acridine orange, and 3,3'-diethyloxacarbocyaninine iodide) was increased both after 4 and 48 hr of respiratory acidosis. However, the number of HCO3(-)-secreting (beta subtype) carbonic anhydrase cells, determined by a probe for the anion exchanger, NBD-taurine, was not increased. In vitro 1% CO2 for 4 hr also resulted in an increase in H+ secretion and in the number of 6-carboxyfluorescein-positive cells, both of which could be blocked with SITS pretreatment. We conclude that CO2 changes the mucosal cells more toward the carbonic anhydrase phenotype, and that if NBD-taurine accurately identifies the beta cells, that the adaptation produces or recruits more alpha-carbonic anhydrase cells.     

The effects of different types of acidosis and extracellular calcium on the mechanical activity of turtle atria

Summary The effects of acidosis and extracellular calcium were examined at 20°C in the isolated spontaneously contracting atria of the freshwater turtle (Chrysemys picta bellii). The atria were subjected to treatments of lactic acidosis, hypercapnic acidosis or chloride acidosis in the presence of both normal (2.0 mM) and high (10.0 mM) calcium, which simulated levels of acidosis and calcium observed in vivo. In all cases of acidosis, pH was reduced to 6.80 from a control pH of 7.80.All three forms of acidosis significantly depressed the force of atrial contraction. During lactic and chloride acidosis a progressive decrease in contractile force was seen, while during hypercapnic acidosis a spontaneous partial recovery was observed following an initial sharp drop in tension. Hypercapnic acidosis had the most rapid effect on contractility, while chloride had the slowest effect.Elevated levels of calcium during lactic and hypercapnic acidoses significantly moderated the negative inotropic effects of acidosis, although contractile force was still below pre-acid values. During chloride acidosis with increased [Ca], no decline in contractile force was observed compared to the control values. Each of the three types of acidoses caused a significant decrease in the frequency of the spontaneous atrial contractions but this effect was not significantly improved with acidosis plus increased [Ca].Based on the present findings and on related observations of acidosis, it appears that the fresh-water turtle is able to compensate for the negative inotropic effects on the heart of both lactic and hypercapnic acidosis, and these compensations may contribute to its remarkable tolerance to anoxia.     

Arteriovenous differences for amino acids and lactate across kidneys of normal and acidotic rats.

1. Arteriovenous differences fro amino acids across kidneys of normal and chronically acidotic rats were measured. Glutamine was the only amino acid extracted in increased amounts in acidosis. There was a considerable production of serine by kidneys from both normal and acidotic rats. 2. The arterial blood concentration of glutamine was significantly decreased in acidotic animals. 3. The glutamine extracted by kidneys of acidotic rats was largely and probably exclusively derived from the plasma. 4. The blood lactate concentration was unchanged in acidosis, as was the uptake of lactate by the kidney.     

Role of acidosis-induced increases in calcium on PTH secretion in acute metabolic and respiratory acidosis in the dog

Recently, we showed that both acute metabolic acidosis and respiratory acidosis stimulate parathyroid hormone (PTH) secretion in the dog. To evaluate the specific effect of acidosis, ionized calcium (iCa) was clamped at a normal value. Because iCa values normally increase during acute acidosis, we now have studied the PTH response to acute metabolic and respiratory acidosis in dogs in which the iCa concentration was allowed to increase (nonclamped) compared with dogs with a normal iCa concentration (clamped). Five groups of dogs were studied: control, metabolic (clamped and nonclamped), and respiratory (clamped and nonclamped) acidosis. Metabolic (HCl infusion) and respiratory (hypoventilation) acidosis was progressively induced during 60 min. In the two clamped groups, iCa was maintained at a normal value with an EDTA infusion. Both metabolic and respiratory acidosis increased (P < 0.05) iCa values in nonclamped groups. In metabolic acidosis, the increase in iCa was progressive and greater (P < 0.05) than in respiratory acidosis, in which iCa increased by 0.04 mM and then remained constant despite further pH reductions. The increase in PTH values was greater (P < 0.05) in clamped than in nonclamped groups (metabolic and respiratory acidosis). In the nonclamped metabolic acidosis group, PTH values first increased and then decreased from peak values when iCa increased by > 0.1 mM. In the nonclamped respiratory acidosis group, PTH values exceeded (P < 0.05) baseline values only after iCa values stopped increasing at a pH of 7.30. For the same increase in iCa in the nonclamped groups, PTH values increased more in metabolic acidosis. In conclusion, 1) both metabolic acidosis and respiratory acidosis stimulate PTH secretion; 2) the physiological increase in the iCa concentration during the induction of metabolic and respiratory acidosis reduces the magnitude of the PTH increase; 3) in metabolic acidosis, the increase in the iCa concentration can be of sufficient magnitude to reverse the increase in PTH values; and 4) for the same degree of acidosis-induced hypercalcemia, the increase in PTH values is greater in metabolic than in respiratory acidosis.     

Na+-H+ exchange in isolated renal brush-border membrane vesicles in response to metabolic acidosis. Kinetic effects

Chronic metabolic acidosis increased the Na+-H+ exchange activity in isolated renal brush-border membrane vesicles. Treatment altered the initial rate of Na+ uptake by increasing Vm (acidotic, 15.3 +/- 0.7 nmol of Na+ X mg-1 X 2 s-1; normal, 11.3 +/- 0.9 nmol of Na+ X mg-1 X 2 s-1), and not the apparent affinity KNa+ (acidotic, 10.2 +/- 0.5 mM; normal 10.2 +/- 0.6 mM). Metabolic acidosis resulted in the proportional increase in 1 mM Na+ uptake at every intravesicular pH measured. A positive cooperative effect on Na+ uptake was found with increased intravesicular acidity in vesicles from both normal and acidotic rats. When the data were analyzed by the Hill equation, it was found that metabolic acidosis did not change the n (acidotic, 1.33 +/- 0.13; normal, 1.43 +/- 0.07) or the K'H+ (acidotic, 0.27 +/- 0.05 microM; normal, 0.28 +/- 0.06 microM), but increased the apparent Vm (acidotic, 1.10 +/- 0.08 nmol of Na+ X mg-1 X 2 s-1; normal, 0.81 +/- 0.07 nmol of Na+ X mg-1 X 2 s-1). The uptake of Na+ in exchange for H+ in membrane vesicles from normal and acidotic animals was not influenced by membrane potential. We conclude that metabolic acidosis leads to either an increase in the number of functioning exchangers or an increase in the turnover rate of the limiting step in the exchange.     

Excess processing of oxidative damaged bases causes hypersensitivity to oxidative stress and low dose rate irradiation

Abstract

Ionizing radiations such as X-ray and γ-ray can directly or indirectly produce clustered or multiple damages in DNA. Previous studies have reported that overexpression of DNA glycosylases in Escherichia coli (E. coli) and human lymphoblast cells caused increased sensitivity to γ-ray and X-ray irradiation. However, the effects and the mechanisms of other radiation, such as low dose rate radiation, heavy-ion beams, or hydrogen peroxide (H₂O₂), are still poorly understood. In the present study, we constructed a stable HeLaS3 cell line overexpressing human 8-oxoguanine DNA N-glycosylase 1 (hOGG1) protein. We determined the survival of HeLaS3 and HeLaS3/hOGG1 cells exposed to UV, heavy-ion beams, γ-rays, and H₂O₂. The results showed that HeLaS3 cells overexpressing hOGG1 were more sensitive to γ-rays, OH^?, and H₂O₂, but not to UV or heavy-ion beams, than control HeLaS3. We further determined the levels of 8-oxoG foci and of chromosomal double-strand breaks (DSBs) by detecting γ-H2AX foci formation in DNA. The results demonstrated that both γ-rays and H₂O₂ induced 8-oxoguanine (8-oxoG) foci formation in HeLaS3 cells. hOGG1-overexpressing cells had increased amounts of γ-H2AX foci and decreased amounts of 8-oxoG foci compared with HeLaS3 control cells. These results suggest that excess hOGG1 removes the oxidatively damaged 8-oxoG in DNA more efficiently and therefore generates more DSBs. Micronucleus formation also supported this conclusion. Low dose-rate γ-ray effects were also investigated. We first found that overexpression of hOGG1 also caused increased sensitivity to low dose rate γ-ray irradiation. The rate of micronucleus formation supported the notion that low dose rate irradiation increased genome instability.     

Renal brush border glutamine transport: comparison between in situ and isolate membrane vesicle uptake

Glutamine uptake by renal cortical brush-border vesicles was compared to transport expressed by the functioning isolated kidney. Comparisons were made with regard to sodium dependency and the adaptive increase induced by chronic metabolic acidosis in the rat. The results show an absolute dependency upon a sodium gradient; sodium-independent glutamine uptake has no counterpart in situ. In addition, acidosis-induced adaptive increase in vesicle glutamine uptake has no counterpart in situ. Rather, the apparent adaptation reflects extravesicular gamma-glutamyltransferase-mediated conversion to glutamate and subsequent accumulation; acidosis-induced adaptation of this enzyme largely explains the apparent adaptation in glutamine uptake. Consequently the role of membrane transport in glutamine flux regulation can be assessed providing metabolic conversion is controlled.     

棉酚对大鼠肾脏γ-谷氨酰转肽酶动力学的影响

本文应用动力学分析观察了棉酚对大鼠肾脏γ-谷氨酰转肽酶(γ-GT)的抑制作用。实验结果证实了棉酚在体外是大鼠肾脏γ-GT的抑制剂,而且抑制常数远小于r-GT的天然抑制剂——马尿酸。在不同浓度的棉酚作用下,改变双底物浓度,测定其活力并应用Lineweaver-Burk双倒数作图法,测得棉酚在两种底物情况下,对γ-GT的抑制作用均呈非竞争性抑制。     

Cardiovascular responses to metabolic and respiratory acidosis and anesthesia in larval Ambystoma tigrinum

Larval Ambystoma tigrinum were examined to determine their cardiovascular responses to three types of acidosis: metabolic acidosis via NH₄Cl gavage; respiratory acidosis via hypercapnia; and anesthetic-induced acidosis, via triacine methanesulphonate. In addition, another group of (metabolic acidosis) animals were tested to determine the role of -mediated catecholamine control on cardiovascular and acid-base regulation. The metabolic and respiratory acidoses produced typical amphibian responses. Anesthesia produced a significant mixed acidosis with respiratory and metabolic components. The cardiovascular responses to metabolic and respiratory acidosis were increased heart rate and pulse pressure. There were no significant changes in diastolic pressure, however, systolic pressure increased as a result of the increased pulse pressure. Animals subjected to metabolic acidosis via -blockade with propranolol did not display the increased heart rate and pulse pressure and the acidosis was deepened and prolonged. Anesthesia resulted in a cardiac slowing and increased pulse pressure, probably explained by the Frank-Starling relationship. There was no change in diastolic pressure. Anesthetized animals had depressed blood O₂ tension and elevated blood lactate.Abbreviations HR heart rate - RBC red blood cell(s) - TMS triacine methanesulphonate     

急性低氧与间断低氧适应对家兔局部血流分布的影响

本实验目的在于探讨急性低氧和间断低氧适应对局部血流分布的影响。我们将26只家兔分为急性低氧,低氧适应和常氧对照三组。在麻醉状态下用放射性标记的蟾蜍红细胞分别测定左心室、双侧肾、双侧肾上腺的血流量;并分区测定了大脑皮质、海马、丘脑下部、脑干的局部脑血流。吸入10％低氧混合气1小时后,急性低氧组脑局部、左心室、肾上腺的血流显著高于对照。经2周间断低氧适应后,低氧适应组脑局部(脑干除外)、左心室、肾上腺的血流下降。两组动物低氧时的肾血流变化不明显。结果提示,2周间断低氧适应能改变局部血流分布,血流的再分布有利于改善机体的抗低氧能力。     

Variations in the kinetic response of several different phosphate-dependent glutaminase isozymes during acute metabolic acidosis

Summary We describe the kinetic modifications to mitochondrial-membrane-bound phosphate-dependent glutaminase in various types of rat tissue brought about by acute metabolic acidosis. The activity response of phosphate-dependent glutaminase to glutamine was sigmoidal, showing positive co-operativity, the Hill coefficients always being higher than 2. The enzyme from acidotic rats showed increased activity at subsaturating concentrations of glutamine in kidney tubules, as might be expected, but not in brain, intestine or liver tissues. Nevertheless, when brain and intestine from control rats were incubated in plasma from acutely acidotic rats enzyme activity increased at 1 mM glutamine in the same way as in kidney cortex. The enzyme from liver tissue remained unaltered. S_0.5 and n_H values decreased significantly in kidney tubules, enterocytes and brain slices preincubated in plasma from acidotic rats. The sigmoidal curves of phosphate-dependent glutaminase shifted to the left without any significant changes in V_max. The similar response of phosphate-dependent glutaminase to acute acidosis in the kidney, brain and intestine confirms the fact that enzymes from these tissues are kinetically identical and reaffirms the presence of an ammoniagenic factor in plasma, either produced or concentrated in the kidneys of rats with acute acidosis.Abbreviations Hepes 4-(2-hydroxyethyl)-1-piperazineethanesulphonic acid - EDTA NN-1,2-Ethane-diylbis [N-(carboxymethyl)glycyne] - Tris 2-amino-2-hydroxymethyl-1,3-propanediol - PDG phosphate dependent glutaminase Publication No. 145 from Drogas, Tóxicos Ambientales y Metabolismo Celular Research Group. Department of Biochemistry and Molecular Biology, University of Granada, Spain