Role of amino acid metabolism in an air-breathing catfish,Clarias batrachus in response to exposure to a high concentration of exogenous ammonia

The air-breathing ureogenic walking catfish (Clarias batrachus) faces various environmental constraints throughout the year leading to the problem of accumulation of toxic ammonia. In the present study, the possible role of conversion of accumulated ammonia to various non-essential free amino acids (FAAs) was tested in this fish under hyper-ammonia stress caused by exposing the fish at 25 mM NH(4)Cl for 7 days. Significant accumulation of ammonia of approximately two- to threefold was observed in different tissues (except in the brain), which was accompanied with the significant accumulation of non-essential FAAs in the NH(4)Cl-exposed fish. There was approximately two- to threefold increase of non-essential FAAs in different tissues and in the plasma of the NH(4)Cl-exposed fish compared to the control fish after 7 days of exposure, which was mainly attributable to the increase of Asp, Ala, Gly, Glu, Gln and taurine (Tau) concentrations in general, with certain tissue-specific variations. This was also accompanied with significant increase of activity of certain amino acid metabolism-related enzymes such as the glutamine synthetase (approx. two- to threefold), glutamate dehydrogenase (ammonia utilizing direction) (approx. twofold), aspartate and alanine aminotransaminases (approx. twofold) mainly in the liver, kidney and muscle of the NH(4)Cl-exposed fish. Thus, it appears that the walking catfish has the capacity of active conversion of accumulated ammonia to non-essential FAAs under condition of high concentrations of external ammonia. However, the increase of urea excretion rate due to active conversion of ammonia to urea via the induced urea cycle appears to be quantitatively much more important pathway than the increase of tissue levels of FAAs in dealing with a severe ammonia load.     

The Role of Ammonium Assimilating Enzymes in Lentil Roots and Nodules

Activities of ammonium assimilating enzymes glutamate dehydrogenase (GDH), glutamine synthetase (GS), glutamate synthase (GOGAT), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) as well as the amino acid content were higher in nodules compared to roots. Their activities increased at 40 and 60 d after sowing, with a peak at 90 d, a time of maximum nitrogenase activity. The GS/GOGAT ratio had a positive correlation with the amino acid content in nodules. Higher activities of AST than ALT may be due to lower glutamine and higher asparagine content in xylem. The data indicated that glutamine synthetase and glutamate synthase function as the main route for the assimilation of fixed N, while NADH-dependent glutamate dehydrogenase may function at higher NH₄ ⁺ concentration in young and senescing nodules. Enzyme activities in lentil roots reflected a capacity to assimilate N for making the amino acids they may need for both growth and export to upper parts of the plant. This revised version was published online in July 2006 with corrections to the Cover Date.     

Air-breathing catfish, Clarias batrachus upregulates glutamine synthetase and carbamyl phosphate synthetase III during exposure to high external ammonia

We assessed the possible upregulation of glutamine synthetase (GS) and typical 'fish type' carbamyl phosphate synthetase III (CPS III) in detoxification of ammonia in different tissues of the walking catfish (Clarias batrachus) during exposure to 25 mM NH(4)Cl for 7 days. Exogenous ammonia led to an increase in ammonia and urea concentrations in different tissues. The results revealed the presence of relatively high levels of GS activity in the brain, liver and kidney, unexpectedly, also in the muscle, and even higher levels in the intestine and stomach. Exposure to high external ammonia (HEA) caused significant increase of activities of GS, CPS III and CPS I-like enzymes, accompanied with the upregulation of GS and CPS III enzyme proteins in different tissues. Exposure to HEA also led to a sharp rise of plasma cortisol level, suggesting being one of the primary causes of upregulation of GS and CPS III enzymes activity. Liver perfusion experiments further revealed that exposure to HEA enhances the capacity of trapping ammonia to glutamine and urea by the liver of walking catfish. These results suggest that the upregulation of GS and CPS III activity in walking catfish during exposure to HEA plays critical roles to ameliorate the toxic ammonia to glutamine, and also to urea via the induced ornithine-urea cycle possibly through the involvement of cortisol.     

Inhibition of glutamine synthesis induces glutamate dehydrogenase-dependent ammonia fixation into alanine in co-cultures of astrocytes and neurons

It has been previously demonstrated that ammonia exposure of neurons and astrocytes in co-culture leads to net synthesis not only of glutamine but also of alanine. The latter process involves the concerted action of glutamate dehydrogenase (GDH) and alanine aminotransferase (ALAT). In the present study it was investigated if the glutamine synthetase (GS) inhibitor methionine sulfoximine (MSO) would enhance alanine synthesis by blocking the GS-dependent ammonia scavenging process. Hence, co-cultures of neurons and astrocytes were incubated for 2.5 h with [U-¹³C]glucose to monitor de novo synthesis of alanine and glutamine in the absence and presence of 5.0 mM NH₄Cl and 10 mM MSO. Ammonia exposure led to increased incorporation of label but not to a significant increase in the amount of these amino acids. However, in the presence of MSO, glutamine synthesis was blocked and synthesis of alanine increased leading to an elevated content intra- as well as extracellularly of this amino acid. Treatment with MSO led to a dramatic decrease in glutamine content and increased the intracellular contents of glutamate and aspartate. The large increase in alanine during exposure to MSO underlines the importance of the GDH and ALAT biosynthetic pathway for ammonia fixation, and it points to the use of a GS inhibitor to ameliorate the brain toxicity and edema induced by hyperammonemia, events likely related to glutamine synthesis.     

Benzoate stimulates glutamate release from perfused rat liver.

In isolated perfused rat liver, benzoate addition to the influent perfusate led to a dose-dependent, rapid and reversible stimulation of glutamate output from the liver. This was accompanied by a decrease in glutamate and 2-oxoglutarate tissue levels and a net K+ release from the liver; withdrawal of benzoate was followed by re-uptake of K+. Benzoate-induced glutamate efflux from the liver was not dependent on the concentration (0-1 mM) of ammonia (NH3 + NH4+) in the influent perfusate, but was significantly increased after inhibition of glutamine synthetase by methionine sulphoximine or during the metabolism of added glutamine (5 mM). Maximal rates of benzoate-stimulated glutamate efflux were 0.8-0.9 mumol/min per g, and the effect of benzoate was half-maximal (K0.5) at 0.8 mM. Similar Vmax. values of glutamate efflux were obtained with 4-methyl-2-oxopentanoate, ketomethionine (4-methylthio-2-oxobutyrate) and phenylpyruvate; their respective K0.5 values were 1.2 mM, 3.0 mM and 3.8 mM. Benzoate decreased hepatic net ammonia uptake and synthesis of both urea and glutamine from added NH4Cl. Accordingly, the benzoate-induced shift of detoxication from urea and glutamine synthesis to glutamate formation and release was accompanied by a decreased hepatic ammonia uptake. The data show that benzoate exerts profound effects on hepatic glutamate and ammonia metabolism, providing a new insight into benzoate action in the treatment of hyperammonaemic syndromes.     

Impact of nitrogen assimilation on regulation of antibiotic production in Streptomyces hygroscopicus 155

The enzymes of the assimilation pathways in cultures of S. hygroscopicus grown in the presence of various nitrogen sources were investigated. No assimilation activity of glutamate dehydrogenase (GDH) was observed. Activities of alanine dehydrogenase (ADH), GDH, glutamine: 2-oxoglutarate aminotransferase (GOGAT) and glutamate synthetase (GS) were studied. High concentrations of ammonium and alanine induced ADH formation. The levels of GS remained low in media with NH4Cl. Various nitrogen sources had no impact on the activity of GOGAT which suggested the involvement of constitutive synthesis. ADH was likely to play an alternative role. Determination of the quantitative and qualitative composition of the free amino acids confirmed the involvement of the GS-GOGAT pathway in nitrogen assimilation. The concentration of ammonium ions in the media with one amino acid or in the presence of several amino acids lowered the antibiotic activity while in the media with alanine and the other nitrogen compounds it increased the antibiotic activity.     

外源γ-氨基丁酸（GABA）对低氧胁迫下甜瓜幼苗根系GABA代谢及氨基酸含量的影响

采用水培法,通过准确控制营养液溶氧浓度,研究了外源γ-氨基丁酸（GABA）对低氧胁迫0~8 d ‘西域一号’甜瓜幼苗根系GABA代谢及氨基酸含量的影响.结果表明：与通气对照相比,低氧处理的甜瓜幼苗正常生长受到严重抑制,其根系谷氨酸脱羧酶（GAD）、谷氨酸脱氢酶（GDH）、谷氨酸合成酶（GOGAT）、谷氨酰胺合成酶（GS）、丙氨酸氨基转移酶（ALT）、天门冬氨酸氨基转移酶（AST）活性以及GABA、丙酮酸、丙氨酸、天冬氨酸含量均显著提高,而谷氨酸和α 酮戊二酸含量在处理4~8 d均显著降低.与低氧处理相比,外源GABA处理有效缓解了低氧胁迫对幼苗根系生长的抑制作用,同时甜瓜根系内源GABA、谷氨酸、α-酮戊二酸、天冬氨酸含量显著提高,但GAD、GDH、GOGAT、GS、ALT、AST活性在整个处理过程中均显著降低,丙酮酸和丙氨酸含量也显著降低.低氧同时添加GABA和γ-乙烯基 γ-氨基丁酸（VGB）处理显著降低了低氧胁迫下GABA的缓解效应.低氧胁迫下外源GABA被植物根系吸收后,通过反馈抑制GAD活性维持较高的Glu含量,保持植物体内碳、氮代谢平衡,维持正常生理代谢,从而缓解低氧胁迫对甜瓜幼苗的伤害.     

African sharptooth catfish Clarias gariepinus does not detoxify ammonia to urea or amino acids but actively excretes ammonia during exposure to environmental ammonia

The African sharptooth catfish Clarias gariepinus lives in freshwater, is an obligatory air breather, and exhibits high tolerance of environmental ammonia. This study aimed at elucidating the strategies adopted by C. gariepinus to defend against ammonia toxicity during ammonia exposure. No carbamoyl phosphate synthetase (CPS) I or III activities were detected in the liver or muscle of the adult C. gariepinus. In addition, activities of other ornithine-urea cycle (OUC) enzymes, especially ornithine transcarbamylase, were low in the liver, indicating that adult C. gariepinus does not have a "functional" hepatic OUC. After being exposed to 50 or 100 mM NH4Cl for 5 d, there was no induction of hepatic OUC enzymes and no accumulation of urea in tissues of the experimental animals. In addition, the rate of urea excretion remained low and unchanged. Hence, ammonia exposure did not induce ureogenesis or ureotely in C. gariepinus as suggested elsewhere for another obligatory air-breathing catfish of the same genus, Clarias batrachus, from India. Surprisingly, the local C. batrachus did not possess any detectable CPS I or III activities in the liver or muscle as had been reported for the Indian counterpart. There were no changes in levels of alanine in the muscle, liver, and plasma of C. gariepinus exposed to 50 or 100 mM NH4Cl for 5 d; neither were there any changes in the glutamine levels in these tissues. Yet even after being exposed to 100 mM NH4Cl for 5 d, there was no significant increase in the level of ammonia in the muscle, which constitutes the bulk of the specimen. In addition, the level of ammonia accumulated in the plasma was relatively low compared to other tropical air-breathing fishes. More importantly, for all NH4Cl concentrations tested (10, 50, or 100 mM), the plasma ammonia level was maintained relatively constant (2.2-2.4 mM). These results suggest that C. gariepinus was able to excrete endogenous ammonia and infiltrated exogenous ammonia against a very steep ammonia gradient. When exposed to freshwater (pH 7.0) with or without 10 mM NH4Cl, C. gariepinus was able to excrete ammonia continuously to the external medium for at least 72 h. This was achieved while the plasma NH4+ and NH3 concentrations were significantly lower than those of the external medium. Diffusion trapping of NH3 through boundary layer acidification can be eliminated as the pH of the external medium became more alkaline instead. These results represent the first report on a freshwater fish (C. gariepinus) adopting active excretion of ammonia (probably NH4+) as a major strategy to defend against ammonia toxicity when exposed to environmental ammonia.     

Nitrogen metabolism of Frankia strain,Cc01, Mg+, At4 and Hr18

The composition and levels of amino acids in four Frankia strains isolated from different actinorhizal plants, were determined. Minor differences in the amino acid profiles were noted with GLN (GLU) being the major amino acid in all four strains. Enzyme actives of ammonia metabolism, GS (glutamine synthetase), GOGAT (glutamate synthetase), and GDH (glutamate dehydrogenase), were also measured. In strains At4 and Hr18, GS and GOGAT activity levels were elevated in N₂-grown cells but significant amounts of GDH activity were present in ammonia-grown cells. No GDH was detected in strain Cc01 and Mg⁺. The characters of heat-stable and heat-labile GSs were described. In N₂-fixing cells, the ATP and amino acid content was much lower, but ammonia content was higher than in NH _inf4 ^sup+ -grown cells.     

Ammonia-Induced Release of Neurotransmitters from Rat Brain Synaptosomes: Differences Between the Effects on Amines and Amino Acids

The effect of NH4Cl on release of amine and amino acid transmitters from rat brain synaptosomes was investigated. Ammonia (0.1-10 mM) stimulated the secretion of dopamine and 5-hydroxytryptamine in a dose-dependent manner, in a process which was additive with the effect of 40 mM K+, almost unaffected by withdrawal of Ca2+, and markedly decreased by increasing [H+] in the medium. The NH4Cl-induced dopamine efflux, in contrast to that caused by high [K+]e, was inhibited by benztropine. The release of gamma-aminobutyric acid, aspartate, and glutamate was unaltered by [NH4Cl] less than 5 mM, but somewhat stimulated at higher levels. Transmembrane pH gradient, acid inside, was dissipated by NH4Cl in a concentration-dependent manner and the internal alkalinization correlated with the stimulation of the rate of dopamine efflux. Transmembrane electrical potential was unaffected by [ammonia] less than 5 mM, but a small depolarization was observed at higher levels. It is postulated that ammonia-induced alkalinization of the intrasynaptic storage granules causes extrusion of amines into the cytoplasm and their subsequent leakage into the medium through a reversal of the plasma membrane transporters. A lack of correlation between the release of amino acid neurotransmitters and the dissipation of the delta pH suggests that in rat brain intrasynaptic vesicles, acidic inside, are unlikely to store substantial amounts of gamma-aminobutyric acid, aspartate, or glutamate.     

Isolation of auxotrophic mutants in support of ammonia assimilation via glutamine synthetase in Methanobacterium ivanovii

Various enzymes involved in the initial metabolic pathway for ammonia assimilation by Methanobacterium ivanovii were examined. M. ivanovii showed significant activity of glutamine synthetase (GS). Glutamate synthase (GOGAT) and alanine dehydrogenase (ADH) were present, wheras, glutamate dehydrogenase (GDH) was not detected. When M. ivanovii was grown with different levels of NH ₊ ⁴ (i.e. 2, 20 or 200 mM), GS, GOGAT and ADH activities varied in response to NH ₊ ⁴ concentration. ADH was not detected at 2 mM level, but its activity increased with increased levels of NH ₊ ⁴ in the medium. Both GS and GOGAT activities increased with decreasing concentrations of NH ₊ ⁴ and were maximum when ammonia was limiting, suggesting that at low NH ₊ ⁴ levels, GS and GOGAT are responsible for ammonia assimilation and at higher NH ₊ ⁴ levels, ADH might play a role. Metabolic mutants of M. ivanovii that were auxotrophic for glutamine were obtained and analyzed for GS activity. Results indicate two categories of mutants: i) GS-deficient auxotrophic mutants and ii) GS-impaired auxotrophic mutants.Abbreviations GS Glutamine synthetase - GOGAT glutamate synthase - GDH glutamate dehydrogenase - ADH alanine dehydrogenase     

Effects of partial hepatectomy on the enzymes of cerebral glutamate and branched-chain amino acid metabolism

Cerebral activities of glutamate dehydrogenase (GDH), glutamine synthetase (GS), and branched-chain amino acid aminotransferase (BCAA-T) along with the levels of ammonia in serum and brain were determined in normal, sham-operated and partially hepatectomized rats. Mild hyperammonemia was observed in sham-operated animals, and the cerebral activities of all the enzymes studied were found to be decreased when compared with those of normal animals. In hepatectomized animals, blood and brain ammonia levels were elevated further. In these animals, GS activity returned to the normal values and that of BCCA-T was elevated, while there was a continued suppression of GDH activity. These results were discussed in relation to the utilization of BCAA (leucine, isoleucine, and valine) for the synthesis of glutamate and glutamine in brain in hyperammonemic states.     

Ammonia-utilizing enzymes of adherent bacteria in the sheep's rumen

In experiments on 6 sheep the authors found the following enzyme activities in bacteria in the rumen fluid, bacteria adhering to the epithelium of the rumen wall and bacteria adhering to food particles in the rumen (given in nkat X g-1 bacterial dry weight): GDH (NADH): 725 +/- 165, 558 +/- 127, 661 +/- 153; GDH (NADPH): 558 +/- 338, 255 +/- 88, 565 +/- 139; GOAT (NADH): 46 +/- 23, 67 +/- 31, 66 +/- 14; GOGAT/NADPH: 58 +/- 27, 56 +/- 15, 65 +/- 29; GS: 153 +/- 65, 69 +/- 35, 71 +/- 32; ALT: 71 +/- 25, 43 +/- 20, 52 +/- 11; AST: 52 +/- 12, 33 +/- 16, 28 +/- 15. The results show that, except for GDH (NADPH), there were no significant differences between the given enzyme activities in the rumen fluid and in bacteria adhering to the rumen wall and to food. Adherent rumen bacteria have the same potential possibilities as the rumen fluid bacteria for the utilization of ammonia, particularly for the synthesis of glutamic acid, glutamine, alanine and aspartic acid, with the above enzymes as catalysts. By means of the GS/GOGAT system, adherent rumen bacteria can probably synthesize glutamic acid in the presence of a limited NH3 concentration in the rumen.     

Alkaline environmental pH has no effect on ammonia excretion in the mudskipper Periophthalmodon schlosseri but inhibits ammonia excretion in the related species Boleophthalmus boddaerti

Experiments were performed to evaluate the effects of alkaline environmental pH on urea and ammonia excretion rates and on tissue urea, ammonia, and free amino acid concentrations in two mudskippers, Periophthalmodon schlosseri and Boleophthalmus boddaerti. Periophthalomodon schlosseri is known to be capable of actively excreting ammonia. The rate of ammonia excretion in B. boddaerti exposed to 50% seawater (brackish water, BW) at pH 9 decreased significantly during the first 2 d of exposure when compared with that of specimens exposed to pH 7 or 8. This suggested that B. boddaerti was dependent on NH(3) diffusion for ammonia excretion, as in most fishes. It was incapable of detoxifying the accumulating endogenous ammonia to urea but could store and tolerate high concentrations of ammonia in the muscle, liver, and plasma. It did not undergo reductions in proteolysis and/or amino acid catabolism in alkaline water, probably because the buildup of endogenous ammonia was essential for the recovery of the normal rate of ammonia excretion by the third day of exposure to a pH 9 medium. Unlike B. boddaerti, P. schlosseri did not accumulate ammonia in the body at an alkaline pH (i.e., pH 9) because it was capable of actively excreting ammonia. Periophthalmodon schlosseri did not undergo partial amino acid catabolism (no accumulation of alanine) either, although there might be a slight reduction in amino acid catabolism in general. The significant decrease in blood pCO(2) in B. boddaerti at pH 9 might lead to respiratory alkalosis in the blood. In contrast, P. schlosseri was able to maintain its blood pH in BW at pH 9 despite a decrease in pCO(2) in the blood. With 8 mM NH(4)Cl in BW at pH 7, both mudskippers could actively excrete ammonia, although not to the same extent. Only P. schlosseri could sustain ammonia excretion against 8 mM NH(4)Cl in BW at pH 8. In BW containing 8 mM NH(4)Cl at pH 9, both mudskippers died within a short period of time. Boleophthalmus boddaerti consistently died faster than did P. schlosseri. This indicates that the body surfaces of these mudskippers were permeable to NH(3), but the skin of P. schlosseri might be less permeable to NH(3) than that of B. boddaerti. Both mudskippers excreted acid (H(+)) to alter the pH of the alkaline external medium. Such a capability, together with modifications in gill morphology and morphometry as in P. schlosseri, might be essential to the development of an effective mechanism for the active excretion of NH+4.     

Role of glutamate dehydrogenase in ammonia assimilation in nitrogen-fixing Bacillus macerans.

Pathways of ammonia assimilation into glutamic acid in Bacillus macerans were investigated by measurements of the specific activities of glutamate dehydrogenase (GDH), glutamine synthetase, and glutamate synthase. In ammonia-rich medium, GDH was the predominant pathway of ammonia assimilation. In nitrogen-fixing cells in which the intracellular NH4+ concentration was 1.4 +/- 0.5 mM, the activity of GDH with a Km of 2.2 mM for NH4+ was found to be severalfold higher than that of glutamate synthase. The result suggests that GDH plays a significant role in the assimilation of NH4+ in N2-fixing B. macerans.     

Ammonia assimilation in Corynebacterium glutamicum and a glutamate dehydrogenase-deficient mutant

In the wild-type of Corynebacterium glutamicum, the specific activity of glutamate dehydrogenase (GDH) remained constant at 1.3 U (mg protein)–1 when raising the ammonia (NH4) concentration in the growth medium from 1 to 90 mM. In contrast, the glutamine synthetase (GS) and glutamate synthase (GOGAT) activities decreased from 1.1 U (mg protein)–1 and 42 mU (mg protein)–1, respectively, to less than 10 % of these values at NH4 concentrations > 10 mM suggesting that under these conditions the GDH reaction is the primary NH4 assimilation pathway. Consistent with this suggestion, a GDH-deficient C. glutamicum mutant showed slower growth at NH4 concentrations 10 mM and, in contrast to the wild-type, did not grow in the presence of the GS inhibitor methionine sulfoximine. © Rapid Science Ltd. 1998     

The African lungfish, Protopterus dolloi, detoxifies ammonia to urea during environmental ammonia exposure

The African lungfish, Protopterus dolloi, was able to maintain a low level of blood plasma ammonia during exposure to high concentrations of environmental ammonia. After 6 d of exposure to 30 or 100 mM NH(4)Cl, the total ammonia concentrations in the blood plasma were 0.288 and 0.289 mM, respectively, which were only 1.7-fold greater than the control value of 0.163 mM. In addition, accumulation of ammonia occurred only in the muscle, but not in the liver. This was achieved in part through urea synthesis, as reflected by significant increases in urea contents in the muscle, liver, and plasma of the experimental animals. In contrast with plasma ammonia, the plasma urea concentrations of specimens exposed to 30 or 100 mM NH(4)Cl for 6 d increased 15.4-fold and 18.8-fold, respectively. Taken together, these results suggest that P. dolloi upregulated the rate of urea synthesis to detoxify ammonia during environmental ammonia exposure and that the increased rate of urea synthesis was fast enough to compensate for the rate of endogenous ammonia production plus the net influx of exogenous ammonia in these experimental animals. Simultaneously, there were increases in the rates of urea excretion in the experimental animals between day 2 and day 6 of environmental ammonia exposure. Interestingly, the rates of urea excretion in specimens exposed to 100 mM NH(4)Cl were lower than those exposed to 30 mM NH(4)Cl, despite the presumably greater load of ammonia to be detoxified to urea in the former situation. It would appear that P. dolloi was regulating the rate of urea excretion during ammonia exposure to retain urea, which might have some physiological functions under environmental stresses yet to be determined. There were decreases in the contents of glutamate, glutamine, and total free amino acids in the liver of the experimental animals, which indirectly suggest that a reduction in the rate of proteolysis and/or amino acid catabolism would have occurred that might lead to a decrease in ammonia production. Our results suggest that, unlike marine elasmobranchs and coelacanths, which synthesize and retain urea for osmoregulatory purposes, the ureogenic P. dolloi was adapted to synthesizing and excreting urea for the purpose of ammonia detoxification.     

Ammonia assimilation and metabolism byBeggiatoa alba

Beggiatoa alba B18LD was investigated for its pathways of ammonia assimilation. The increase in growth yields ofB. alba with excess acetate was linear from 0.1 to 2.0 mM ammonia.B. alba had strong glutamine synthetase (GS) and glutamate synthase (GOGAT) activities, irrespective of the ammonia concentration in the medium. Glutamate dehydrogenase activity was not found, and alanine dehydrogenase (aminating) was observed only whenB. alba was grown at high (2.0 mM) ammonia. Methionine sulfoximine, an inhibitor of GS, inhibited growth ofB. alba irrespective of the ammonia concentration in the medium. Thus it appears the primary pathway for ammonia assimilation inB. alba is via the GS-GOGAT pathway at both low and high ammonia concentrations. Preliminary experiments were unable to discern if theB. alba GS is modified by covalent modification.Non-standard abbreviations GS Glutamine synthetase - GOGAT glutamate-oxoglutarate aminotransferase - GDH glutamate dehydrogenase - ADH alanine dehydrogenase - MSX methionine sulfoximine - GOT glutamate-oxaloacetate aminotransferase - GPT glutamate-pyruvate aminotransferase     

Urate synthesis in the perfused chick liver

Urate synthesis was studied in a perfused chicken liver preparation. The perfused liver had an ATP/ADP ratio of 0.29+/-0.05(6) compared with 0.34+/-0.07(10) in liver obtained from chicks under ether anaesthesia. Lactate/pyruvate ratios were 9.4+/-1.7(5) in the perfused liver and 14.8+/-1.8(5) in the rapidly sampled liver. Urate synthesis was only marginally stimulated by glycine, glutamine, aspartic acid or NH(4)Cl, but significant increases were observed with phosphoribosyl pyrophosphate, aminoimidazolecarboxylic acid riboside, inosine, inosinic acid and xanthine. Urate synthesis from glycine, glutamine, NH(4)Cl, asparagine, alanine, histidine and a mixture of 21 amino acids was obtained on inclusion of insulin in the perfusion medium. Evidence for the inclusion of the carbon of histidine into uric acid was obtained. Aspects of the energy consumption associated with the conversion of excess of amino acid into uric acid are considered.     

Dietary amino acid taurine ameliorates liver injury in chronic hepatitis patients

The effect of dietary amino acid taurine on the liver function of chronic hepatitis patients was investigated. The 24 chronic hepatitis patients with 2-5 times over normal activities of alanine aminotransferase (ALT) or aspartate aminotransferase (AST) were selected and equally divided into taurine treatment and control groups. In taurine treatment group, each patient took 2 g taurine 3 times a day for three months, and then stopped treatment for 1 month. Patients taking placebo without taurine for 4 months served as a control group. ALT and AST activities and levels of cholesterol, triglyceride and thiobarbituric acid relative substances of serum plasma in the taurine group were all decreased at the end of three month treatment. The study suggested that dietary amino acid taurine may ameliorate liver injury for chronic hepatitis patients.