Studies on utilization of 2-ketoglutarate,glutamate and other amino acids by the unicellular alga Cyanidium caldarium

Two strains of Cyanidium caldarium which possess different biochemical and nutritional characteristics were examined with respect to their ability to utilize amino acids or 2-ketoglutarate as substrates.One strain utilizes alanine, glutamate or aspartate as nitrogen sources, and glutamate, alanine or 2-ketoglutarate as carbon and energy sources for growth in the dark. The growth rate in the dark on 2-ketoglutarate is almost twice as high or higher than that on glutamate or alanine. During growth or incubation of this alga on amino acids, large amounts of ammonia are formed; however, ammonia formation is strongly inhibited by 2-ketoglutarate. The capacity of the alga to form ammonia from amino acids is inducible and develops fully only when the cells are grown or incubated in the presence of glutamate.By contrast, the other strain of Cyanidium caldarium cannot utilize alanine or aspartate as nitrogen sources. It utilizes glutamate only very poorly and does not excrete ammonia into the external medium. This strain is unable to utilize amino acids or 2-ketoglutarate as carbon and energy sources for heterotrophic growth.Cell-free extracts were tested for the occurrence of enzymes which could account for amino acid metabolism and ammonia formation.     

ACTIONS OF l-GLUTAMATE AND RELATED AMINO ACIDS ON OXYGEN UPTAKE, LACTATE PRODUCTION AND NADH LEVELS OF RAT BRAIN IN VITRO

Abstract— A range of acidic amino acids differing in (i) their potency as neuronal excitants, (ii) their transport properties and (iii) their ability to act as substrates for metabolism have been compared with respect to their effects on energy metabolism of rat cerebral cortex in vitro. l -Glutamate, and d - and l -homocysteate, increased tissue slice NADH levels, and the same three amino acids, together with d -glutamate and kainate, increased oxygen uptake by the slices. It was concluded that these effects were predominantly due to neuronal depolarization and the ensuing activation of ion pump mechanisms. l -Glutamate, d -glutamate and l -homocysteate increased lactate production by the slices, whereas d -homocysteate and kainate did not. Since the two latter amino acids are the strongest neuroexcitants but probably the least rapidly transported, it is suggested that stimulation of lactate production in slices by amino acid excitants is a consequence of the energy requirements of active uptake of the amino acids, and probably occurs mainly in glial cells. Although the metabolism of l -glutamate appeared not to be an essential requirement for the effects observed with this amino acid in the present work, such metabolism may make a proportionately greater contribution under sub-optimal conditions of slice preparation and incubation, where electrical activity of the tissue may be impaired.     

Heterotrophic growth patterns in the unicellular alga Cyanidium caldarium

A strain of Cyanidium caldarium has been studied which is able to grow in darkness using amino acids as sole energy sources. During growth ammonia was released into the external medium as a catabolic end product. With either threonine or glutamate similar rates of ammonia formation and similar kinetics of growth were observed. These observations suggest that the amounts of energy made available for cell growth from the two amino acids are equivalent.Deamination of threonine and glutamate by whole cells exhibited similar temperature-dependence profiles and similar Arrhenius energies of activation. Thus it is suggested that a partially common pathway is involved in the catabolism of these amino acids. Threonine dehydrase may play a role in this pathway.The threonine dehydrase of C. caldarium was inhibited by isoleucine and activated by valine. In the absence of isoleucine no cooperative effect of threonine was observed.Succinate or 2-ketoglutarate supported a faster growth than did amino acids. Growth tests in the presence of both a krebs cycle intermediate and an amino acid have shown that the oxidative metabolism of amino acids is in some way controlled by the more suitable energy sources, presumably through catabolite inhibition and catabolite repression.     

Amino acid consumption by the parasitic, amoeboid protists Entamoeba histolytica and E. invadens

Abstract Amino acid consumption by Entamoeba histolytica and E. invadens has been measured in order to assess the possible roles of amino acids as energy substrates. Mixtures of amino acids enhanced the growth of the parasites in complex medium and their survival in simple medium. The consumption of several amino acids by the parasites suspended in simple media was greater when glucose was absent, suggesting that they may act as alternative energy sources. Under these conditions, asparagine was consumed extremely rapidly by E. histolytica in particular, and arginine, leucine and threonine were used greatly by both species. There was also a marked consumption of aspartate, but this occurred even when glucose was present. These five amino acids and phenylalanine were the ones consumed in greatest amounts during growth of E. histolytica in complex medium. Under the same growth conditions, E. invadens also used asparagine, arginine, leucine and threonine and in addition there was a large consumption of serine and especially glutamate. In contrast, the aspartate concentration in the complex medium increased and there was also a net increase in the concentration of some other amino acids. Alanine was produced by both species when the parasites were incubated in simple medium with glucose, and in greater amounts during growth in complex media, suggesting that it is an end product of energy metabolism. The findings provide support for the suggestion that energy generation through amino acid catabolism may be a characteristic feature of anaerobic parasitic protists.     

氨基酸转运体在肿瘤代谢中的研究进展

代谢重编程是肿瘤的重要特征,是指肿瘤细胞为满足其快速增殖的生物合成与能量需求,对其糖代谢、脂代谢以及氨基酸代谢等代谢路径进行的重编程,以维持增长速度以及补偿能量代谢所造成的氧化还原压力。虽然不同的癌症代谢变化不同,但有些特征是所有癌症共有的,氨基酸代谢重编程是其中一个重要的特征。氨基酸进出细胞需要氨基酸转运体的协助,因而在肿瘤细胞中多种特定的氨基酸转运体均过表达。靶向氨基酸转运体通过影响肿瘤细胞的氨基酸代谢从而达到抗肿瘤的目的,是目前抗肿瘤药物的研究热点之一。主要介绍了几种在肿瘤代谢中发挥重要作用的氨基酸转运体以及靶向氨基酸转运体抗肿瘤治疗的研究进展及相关作用机制,旨在了解氨基酸转运体在抗肿瘤研究中的作用,以期促进靶向氨基酸转运体抗肿瘤药物的发展。     

Role of Amino Acids and Vitamins in Nutrition of Mesophilic Methanococcus spp

In this study we found that autotrophic methanococci similar to Methanococcus maripaludis obtained up to 57% of their cellular carbon from exogenous amino acids. About 85% of the incorporation was into protein. Primarily nonpolar and basic amino acids and glycine were incorporated; only small amounts of acidic and some polar amino acids were taken up. An additional 10% of the incorporation was into the nucleic acid fraction. Because little ¹⁴CO₂ was formed from the ¹⁴C-amino acids, little metabolism of the amino acids occurred. Therefore the growth stimulation by amino acids was probably due to the sparing of anabolic energy requirements. Of the amino acids incorporated, only alanine was also a sole nitrogen source for these methanococci. In contrast, Methanococcus vannielii and “Methanococcus aeolicus” are autotrophic methanococci which did not incorporate amino acids and did not utilize alanine as a sole nitrogen source. Although glutamine served as a sole nitrogen source for the autotrophic methanococci and Methanococcus voltae, a heterotrophic methanococcus, growth was due to chemical deamination in the medium. M. voltae requires leucine and isoleucine for growth. However, these amino acids were not significant nitrogen sources, and alanine was not a sole nitrogen source for the growth of M. voltae. The branched-chain amino acids were not extensively metabolized by M. voltae. Pantoyl lactone and pantoic acid were readily incorporated by M. voltae. The intact vitamin pantothenate was neither stimulatory to growth nor incorporated. In conclusion, although amino acids and vitamins are nutritionally important to both autotrophic and heterotrophic methanococci, generally they are not subject to extensive catabolism.     

Workshop 4: Compartmentation of Neuronal Metabolism. Compartmentation of energy metabolism and amino acid synthesis in synaptosomes

There is strong evidence that the brain can use multiple substrates for energy including glucose, lactate, ketone bodies, glutamate and glutamine. Competition studies show that certain substrates are preferentially used for energy by synaptic terminals even when other substrates are available. It has recently been shown that synaptosomes can use both glutamine and glutamate for energy and synthesis of amino acids; however, these substrates yield very different patterns of 13C‐labelling of end products. These findings provide evidence of differential compartmentalisation of the metabolism of glutamate taken up from the extracellular milieu as compared to the glutamate produced from glutamine within synaptic terminals. This compartmentalisation is related to the specific role(s) of glutamate vs. glutamine in synaptic terminals as well as the metabolism of these amino acids in either partial or complete TCA cycles for energy. The presence of glucose, which provides a source of acetyl‐CoA, can greatly modulate both the metabolic fate of other substrates and the pool size of amino acids such as glutamate and GABA. The differential localization of the enzymes glutamate dehydrogenase and aspartate aminotransferase contribute to this compartmentalisation as does the necessity that synaptic terminals balance their energy needs with the requirement to synthesize neurotransmitters.     

A comparison of the requirements for various carbon and nitrogen sources and vitamins in some Frankia isolates

Summary It was established that anAlnus glutinosa isolate (LDAgp 1) is able to utilize mono- and disaccharides and shows a limited growth ability on arabinose and starch. This contrasts with an isolate fromAlnus viridis (AvcI 1) andComptonia peregrina (CpI1), which apparently lack glycolytic pathway activity. These latter isolates can utilize some tricarboxylic acids in contrast to LDAgp1. Volatile fatty acids or their salts, such as propionic acid and acetate, were utilized by all three isolates. Besides a general ability to utilize inorganic nitrogen sources, some amino acids and urea, selected isolates showed a limitedability to utilize adenine and uracil. A simple, synthetic medium based on propionic acid as the energy source was developed. On this medium some isolates showed growth stimulation in the presence of biotin. The metabolic aspects of the utilization of carbon and nitrogen sources, as well as some ecological consequences are discussed.     

Compartmentalized neurotransmitter and amino acid synthesis in vivo studied by high field MRS

There is strong evidence that the brain can use multiple substrates for energy including glucose, lactate, ketone bodies, glutamate and glutamine. Competition studies show that certain substrates are preferentially used for energy by synaptic terminals even when other substrates are available. It has recently been shown that synaptosomes can use both glutamine and glutamate for energy and synthesis of amino acids; however, these substrates yield very different patterns of 13C-labelling of end products. These findings provide evidence of differential compartmentalisation of the metabolism of glutamate taken up from the extracellular milieu as compared to the glutamate produced from glutamine within synaptic terminals. This compartmentalisation is related to the specific role(s) of glutamate vs. glutamine in synaptic terminals as well as the metabolism of these amino acids in either partial or complete TCA cycles for energy. The presence of glucose, which provides a source of acetyl-CoA, can greatly modulate both the metabolic fate of other substrates and the pool size of amino acids such as glutamate and GABA. The differential localization of the enzymes glutamate dehydrogenase and aspartate aminotransferase contribute to this compartmentalisation as does the necessity that synaptic terminals balance their energy needs with the requirement to synthesize neurotransmitters.     

Amino acid and energy requirements for rat hepatocytes in primary culture

Summary The amino acid and energy requirements of rat hepatocytes in suspension and early culture were investigated. Among a number of potential energy substrates tested, pyruvate (20 mM) was found to be most effective in stimulating hepatocytic protein synthesis. Amino acids stimulated protein synthesis both as energy substrates and as protein precursors. An amino acid mixture was designed to provide maximal inhibition of protein degradation as well as maximal stimulation of protein synthesis. In a defined medium containing amino acids at these concentrations, and supplemented with glucocorticoid hormone and insulin, hepatocytes could be maintained—on a collagen substratum—for at least a week without any significant net loss of cells or cellular protein. The work was supported by grants from The Norwegian Cancer Society and from The Norwegian Council for Science and the Humanities. An erratum to this article is available at .     

The Effect of Some Protein and Non-Protein Amino Acids on the Growth of Cladosporium herbarum and Trichothecium roseum

The effect of ten amino acids as the sole nitrogen source for the growth of Cladosporium herbarum (Link.) Fr. and Trichothecium roseum (Bull.) Link. was studied in order to clarify the fungus-host plant relationship. Special attention was paid to some rare non-protein amino acids of legumes. The best nitrogen sources for both fungi were γ-aminobutyric acid, arginine, serine and proline. Cladosporium could use homoarginine and canavanine, but these two amino acids were not used by Trichothecium when each was given as the only nitrogen source. Both fungi utilized ornithine, homoserine and a,γ-diaminobutyric acid to a limited extent. Pipecolic acid was not growth promoting. The growth-retarding effects of rare non-protein amino acids (homoarginine, canavanine, a,γ-diaminobutyric acid and pipecolic acid) were usually reversed by higher concentrations of their normal analogues. It is possible that rare non-protein amino acids may slightly protect the host plant against fungal infections, but there are clear differences between fungi in their reaction to non-protein amino acids.     

Amino acid utilization by the ruminal bacterium Synergistes jonesii strain 78-1

The ruminal bacterium Synergistes jonesii strain 78-1, which is able to degrade the pyridinediol toxin in the plant Leucaena leucephala, was studied for its ability to utilise amino acids. The organism used arginine, histidine and glycine from a complex mixture of amino acids, and both arginine and histidine supported growth in a semi-defined medium. The products of (U-¹⁴C)-arginine metabolism were CO₂ acetate, butyrate, citrulline and ornithine. The labelling pattern of end products from (U-¹⁴C)-histidine metabolism differed in that carbon also flowed into formate and propionate. Arginine was catabolised by the arginine deiminase pathway which was characterised by the presence of arginine deiminase, ornithine transcarbamylase and carbamate kinase. This is the first report of a rumen bacterium that uses arginine and histidine as major energy yielding substrates.     

Amino acid degradation by the mesophilic sulfate-reducing bacterium Desulfobacterium vacuolatum

Desulfobacterium vacuolatum strain IbRM was able to grow using casamino acids as a source of carbon, energy and nitrogen. Growth was accompanied by utilization of several amino acids and sulfide production. Proline and glutamate were used preferentially and to the greatest extent. Glycine, serine and alanine were used more slowly and only after proline and glutamate were used. Isoleucine, valine, leucine and aspartate decrease was slowest and occurred in a linear fashion throughout the growth phase. Amino acids used from casamino acids, excluding aspartate, were also used as single carbon, energy and nitrogen sources. As a single amino acid, aspartate could only be used as a nitrogen source. Aspartate was not used as an electron acceptor. No growth occurred on any amino acid in the absence of sulfate. As single substrates, isoleucine, proline and glutamate were oxidized without formation of acetate and with molar yields of 13.1, 9.4 and 7.7 g mol^–1, respectively. Received: 24 June 1997 / Accepted: 10 September 1997     

Ontogenesis of catabolic and energy metabolism capacities during the embryonic development of spotted wolffish (Anarhichas minor)

The catabolic and energy metabolism capacities during spotted wolffish (Anarhichas minor) embryogenesis were investigated. We assessed the embryo's ability to catabolize proteins (trypsin-like proteases) and lipids (triglyceride lipase) and examined the development of metabolic capacities using enzymatic assays: ability to use carbohydrates (pyruvate kinase), amino acids (aspartate aminotransferase) and fatty acids (hydroxyacyl-CoA dehydrogenase) for energy production, and aerobic (citrate synthase) and anaerobic (lactate dehydrogenase) energy production. Functional enzymatic systems were detected from the eyed stage (350 degree-days), except for fatty acids, which was detected from 540 degree-days. To compare the development of 1) aerobic and anaerobic pathways and 2) the capacity to mobilize the different energy substrates, enzymatic ratios were calculated. Anaerobic capacity appeared to increase at a significantly higher rate than the aerobic capacity. Ratios revealing the relative capacity to use specific energy substrates showed a significantly slower increase during development in the capacity to use carbohydrates than amino acids and fatty acids. The end of embryogenesis was characterized by a significant decrease in the use of carbohydrates for aerobic energy production but an increasing capacity to use amino acids. Egg survival as affected by the variability in metabolic parameters is discussed.     

UPTAKE SPECIFICITY FOR ORGANIC SUBSTRATES BY THE MARINE DIATOM MELOSIRA NUMMULOIDES1

Melosira nummuloides, clone Mel-3, shows a very high specificity with regard to its ability to take up organic substrates. Amino acids supplied in the medium at 1 X 10^-4 M are taken up at initial rates of the same order of magnitude as that of photoassirnilation of COj. However, sugars, sugar alcohols, or organic acids supplied at the same concentration are not taken up. The mechanism for uptake of amino acids appears to require energy, since tlie uptake of the amino acid analog α-aminoisobutyric acid is strongly inhibited by 2 f-dinitrophenul. The uptake mechanism does not appear to be inducible. The ability of M. numinuloides to utilize amino acids as a nitrogen source is quite restricted. Arginine, ghttamine, asparagine, proline, and glutamic acid were good nitrogen sources. Seventeen other amino acids, including α-aminoisobutyric acid, were unsatisfactory for growth, although they were rapidly taken up from the medium.     

Effect of Dipeptides on the Growth of <Emphasis Type="Italic">Oenococcus oeni</Emphasis> in Synthetic Medium Deprived of Amino Acids

Oenococcus oeni has numerous amino acid requirements for growth and dipeptides could be important for its nutrition. In this paper the individual or combined effect of dipeptides on growth of O. oeni X₂L in synthetic media deficient in one or more amino acids with L-malic acid was investigated. Utilization of dipeptides, glucose, and L-malic acid was also analyzed. Dipeptides were constituted by at least one essential amino acid for growth. Dipeptides containing two essential amino acids, except leucine, had a more favorable effect than free amino acids on the growth rate. Gly-Gly was consumed to a greater extent than Leu-Leu and a rapid exodus of glycine to the extracellular medium accompanied it. The microorganism could use glycine in exchange for other essential amino acids outside the cell, favoring growth. In the presence of Leu-Leu, the increase in glucose consumption rate could be related to the additional energy required for dipeptide uptake.     

Control by amino acids of the activity of system A-mediated amino acid transport in isolated rat hepatocytes.

The effect of amino acids, in concentrations corresponding to those found in the portal vein of rats given a high-protein diet, was investigated on the activity of system A amino acid transport in hepatocytes from fed rats. Amino acids counteracted the induction of system A by insulin or glucagon. This effect was observed at all concentrations of hormones tested, up to 1 microM. Amino acids did not affect the basal cyclic AMP concentration in hepatocytes, or the large rise in cyclic AMP elicited by glucagon. The reversal of system-A induction was observed at relatively low concentration of amino acids, corresponding to plasma values reported in rats given a basal diet. Amino acids were separately tested: substrates of system A were particularly efficient, but so were glutamine and histidine. Non-metabolizable substrates of system A, such as 2-aminoisobutyrate, were also inhibitory, suggesting that a part of the effect of amino acids is independent of their cellular metabolism. Provision of additional energy substrates such as lactate and oleate did not affect induction of system A or the inhibitory effects of amino acids. Thus amino acids do not act by serving as an energy source and by maintaining the integrity of hepatocytes. Inhibition of mRNA synthesis by actinomycin practically abolished the effect of amino acids on the induction of system A by glucagon. The results suggest that amino acids may promote the synthesis of protein(s) affecting the activity of system A either directly at the carrier unit or at an intermediate stage of its emergence.     

A natural isolate of Pseudomonas maltophila which degrades aromatic sulfonic acids

Abstract A natural isolate, designated BSA56, which was originally selected for growth with benzene sulfuric acid as sole carbon and energy source, was identified as a strain of Pseudomonas maltophila . Strain BSA56 grew on a wide range of aromatic sulfonic acids and was shown to release sulfite from benzene sulfonic acid and 2-napthalene sulforic acid. Although it also grew on toluene sulfonic acid and pyridine sulfonic acid, no significant sulfite release was observed with these substrates. Release of sulfite from benzene sulfonic acid was greatly promoted by the presence of glycerol. The ability to release sulfite was induced by growth in the presence of benzene sulfonic acid and was repressed almost entirely by substrates allowing rapid growth such as acetate. Strain BSA56 grew better at 30°C than 37°C on most aromatic substrates, but the reverse was true for most aromatic sulfonates. Several mutants of BSA56 were isolated with defects in benzoate, salicylate, or gentisate metabolism. However, all these mutants retained the ability to degrade the aromatic sulfonates.