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At least 19 recordsLinked to original sources
PubMed1977

Role of protein dissociation in the transport of acidic amino acids by the Ehrlich ascites tumor cell.

The pH profile for the uptake of L-glutamic acid by the Ehrlich ascites tumor cell arises largely as a sum of the decline with falling pH of a slow, Na+-dependent uptake by System A, and an increasing uptake by Na+-independent System L. The latter maximizes at about pH 4.5, following approximately the titration curve of the distal carboxyl group. This shift in route of uptake was verified by (a) a declining Na+-dependent component, (b) an almost corresponding decline in the 2-(methylamino)-isobutyric acid-inhibitable component, (c) a rising component inhibited by 2-aminonorbornane-2-carboxylic acid. Other amino acids recognized as principally reactive with Systems A or L yielded corresponding inhibitory effects with some conspicious exceptions: 2-Aminoisobutyric acid and even glycine become better substrates of System L as the pH is lowered; hence their inhibitory action on glutamic acid uptake is not lost. The above results were characterized by generally consistent relations among the half-saturation concentrations of the interacting amino acids with respect to: their own uptake, their inhibition of the uptake, one by another, and their trans stimulation of exodus, one by another. A small Na+-dependent component of uptake retained by L-glutamic acid but not by D-glutamic acid at pH 4.5 is inhibitable by methionine but by neither 2-(methylamino)-isobutyric acid nor the norbornane amino acid. We provisionally identified this component with System ASC, which transports L-glutamine throughout the pH range studied. No transport activity specific to the anionic amino acids was detected, and the unequivocally anionic cysteic acid showed neither significant mediated uptake nor inhibition of the uptake of glutamic aic or of the norbornane amino acid. The dicarboxylic amino acids take the sequence, aspartic acid less than glutamic acid less than alpha-aminoadipic acid less than S-carboxymethylcysteine, in their rate of mediated, Na+-independent uptake at low pH. Diiodotyrosine and two dissimilas isomers of nitrotyrosine also show acceleration of uptake as the phenolate group on the sidechain is protonated, a result indicating that the acidic group need not be a carboxyl group and need not take a specific position in space to be accepted at the receptor site L. The presence of the carboxyl group does not upset the normal stereospecificity of System L until it falls on the beta-carbon in aspartic acid; even then it is the presence of the carbonyl group and not of the intact carboxyl group nor of its hydroxyl group that cancels out the stereospecificity, as was shown by the absence of normal stereospecificity for aspartic acid and asparagine and its presence in glutamic acid, homoserine and glutamine. In agreement, the uptak of aspartic acid is peculiarly sensitive to the presence of an alpha-methyl group or of other structures that modify the orientation of the sidechain.

Amino Acids↗
PubMed1979

The effect of acidic amino acid antagonists on synaptic transmission in the hippocampal formation in vitro.

The effects on synaptic efficacy of the putative acidic amino acid antagonists, 2-amino-4-phosphonobutyric acid (APB), 2-amino-3-phosphonopropionic acid (APP), 1-hydroxy-3-amino-pyrrolidone-2 (HA-966) and glutamic acid diethyl ester (GDEE), were tested by bath application to the hippocampal slice preparation. On the basis of previous work, we hypothesized that APB, HA-966 and GDEE might antagonize synaptic responses to either glutamate or aspartate, but APP should antagonize only synaptic responses to aspartate. APB and HA-966 reduced the amplitude of the extracellular EPSP recorded during stimulation of the perforant path fibers, but APP and GDEE were without effect. APB, APP and HA-966, but not GDEE, consistently inhibited transmission at Schaffer collateral and commissural synapses. The mossy fiber evoked extracellular EPSP was unaffected by these agents. At the concentrations used in this study (usually 2.5 mM) none of these drugs affected the amplitude of presynaptic fiber potentials or antidromic responses, indicating that they probably acted at synapses. The spontaneous activity of hippocampal pyramidal cells, but not of dentate granule cells, increased in the presence of 2.5 mM APB. The amplitude of the population spike generated by Schaffer commissural stimulation initially increased following introduction of APB into the medium and then declined in parallel with the extracellular EPSP. In addition, APB reduced the duration of recurrent inhibition during the period when pyramidal cell firing was enhanced. These results can be explained by an antagonism at the synapse between pyramidal cell and inhibitory interneuron.

Afferent Pathways↗
PubMed1979

Effect of N-trifluoroacetyl derivatives of amino acids and amino acid analogs on microbial antitumor screen.

Eighteen trifluoroacetyl derivatives of amino acids and of amino acid analogs were prepared and tested for growth-inhibitory activity using a Lactobacillus casei system as a prescreen for antitumor activity. Of the compounds tested, the trifluoroacetyl derivatives of o-, m-, and p-fluorophenylalanine and of beta-3-thienylalanine showed modest activity; trifluoroacetyl derivatives of phenylalanine and of beta-2-thienylalanine showed marginal activity. The activity exhibited by the active trifluoroacetyl compounds was equal to that noted for most active chloroacetyl derivatives reported previously, as judged by comparison of their activity with that of chloroacetyl-m-fluorophenylalanine. No reversal of inhibition was noted when a representative of these inhibitors was challenged with a corresponding natural metabolite, both as a free amino acid and as a noninhibitory acylated compound.

Amino Acids↗
PubMed1979

N-Benzoyl derivatives of amino acids and amino acid analogs as growth inhibitors in microbial antitumor screen.

Twenty-seven N-benzoyl derivatives of amino acids and amino acid analogs were prepared and tested for growth-inhibitory activity in a microbial antitumor screen. Of these, 19 showed some inhibitory capacity, from a modest 13% to a potent 96% at 1 mg/ml. The activities of the "modest" inhibitors were comparable to those of most inhibitory chloracetyl and trifluoroacetyl derivatives reported earlier. The intermediate inhibitors were as active as N-chloroacetyl-beta-hydroxy-D-norleucine isomer B, the most active acyl derivative noted previously. The most active compounds in this study were N-benzoyl-p-chloro-DL-phenylalanine and N-benzoyl-m-fluoro-DL-phenylalanine, which inhibited the test organism almost completely under the assay conditions.

Amino Acids↗
PubMed1978

D-Amino acids of the amino acid pool and occurrence of racemase and D-amino acid oxidase activities in Escherichia coli B.

Less than 20% of the amino acid content of the amino acid pool of Escherichia coli B exists in the D-form. Alanine, glutamic acid, and valine were shown by gas- chromatography to be partially in the D-form. Only D-alanine was formed by racemization in the crude extract of this organism. Alanine racemase was easily released from the membranes or vesicles but D-alanine oxidase activity remained firmly bound to the membrane. Most protein amino acids stimulated proline uptake into the vesicles, and the oxidative deamination activities were verified by the proline uptake stimulating amino acids. It is concluded that the obligatory pathway of L-amino acid--D-amino acid--oxo acid which exists in the oxidation of L-alanine does not exist with other L-amino acids. It is likely that other D-amino acids in the pool are formed in the presence of D-amino acid oxidase or D-amino acid aminotransferase.

Alanine Racemase↗
PubMed1979

Glucagon-induced autophagy and proteolysis in rat liver: mediation by selective deprivation of intracellular amino acids.

Amino acid deprivation and glucagon are both potent inducers of autography and proteolysis in liver. Because glucagon enhanced the metabolic utilization of some amino acids, the catabolic response to both of these stimuli could be achieved by a lowering of intracellular amino acid pools. Alternatively, glucagon could act independently of amino acids. To clarify the mode of hormonal action and also the relationship between the two cellular responses, livers from fed rats were perfused, with and without glucagon, with plasma amino acids over a concentration range of 0 to 10 times normal. Individual amino acids constancy at each level was ensured by perfusion in the single-pass mode. Amino acids alone strongly regulated autophagy and proteolysis in a coordinated fashion; maximal suppression was achieved at twice normal concentration; both effects increased rapidly to maximum at less than normal concentration. Corresponding effects of glucagon, however, could be elicited only at intermediate amino acid levels. None was noted at 4 and 10 times normal; at 0, hormonal stimulation was minimal. The amino acid inhibition was selective because it did not block cyclic AMP production or glycogenolysis. Intracellular pool measurements and systematic alteration of perfusate amino acid composition indicated that the autophagic and proteolytic effects of glucagon are mediated by a hormonally induced depletion of glycine, alanine, glutamate, and glutamine; of these, glutamine alone is the most effective. We conclude that the stimulation of intracellular protein degradation in liver is a manifestation of deprivation-induced autophagy which results from a decrease in certain intracellular glucogenic amino acids, notably glutamine.

Amino Acids↗
PubMed1977

Derepression of amino acid transport by amino acid starvation in rat hepatoma cells.

Amino acid starvation causes an adaptive increase in the initial rate of transport of selected neutral amino acids in an established line of rat hepatoma cells in tissue culture. After a lag of 30 min, the initial rate of transport of alpha-aminoisobutyric acid (AIB) increases to a maximum after 4 to 6 h starvation of 2 to 3 times that seen in control cells. The increased rate of transport is accompanied by an increase in the Vmax and a modest decrease in the Km for this transport system, and is reversed by readdition of amino acids. The enhancement is specific for amino acids transported by the A or alanine-preferring system (AIB, glycine, proline); uptake of amino acids transported by the L or leucine-preferring system (threonine, phenylalanine, tyrosine, leucine) or the Ly+ system for dibasci amino acids (lysine) is decreased under these conditions. Amino acids which compete with AIB for transport also prevent the starvation-induced increase in AIB transport; amino acids which do not compete fail to prevent the enhancement. Paradoxically threonine, phenylalanine, tryptophan, and tyrosine, which do not compete with AIB for transport, block the enhancement of transport upon amino acid starvation. The starvation-induced enhancement of amino acid transport does not appear to be the result of a release from transinhibition. After 30 min of amino acid starvation, AIB transport is either unchanged or slightly decreased even though amino acid pools are already depleted. Furthermore, loading cells with high concentrations of a single amino acid following a period of amino acid starvation fails to prevent the enhancement of AIB transport, whereas incubation of the cells with the single amino acid for the entire duration of amino acid starvation prevents the enhancement; intracellular amino acid pools are similar under both conditions. The enhancement of amino acid transport requires concomitant RNA and protein synthesis, consistent with the view that the adaptive increase reflects an increased amount of a rate-limiting protein involved in the transport process. Dexamethasone, which dramatically inhibits AIB transport in cells incubated in amino acid-containing medium, both blocks the starvation-induced increase in AIB transport, and causes a time-dependent decrease in transport velocity in cells whose transport has previously been enhanced by starvation.

Amino Acids↗
PubMed1978

Effect of acylated amino acids and acylated amino acid analogs on microbial antitumor screen.

A series of N-acetyl,-N-propionyl, and N-chloroacetyl derivatives of amino acids and amino acid analogs was tested for growth-inhibitory activity using a Lactobacillus casei system as a prescreen for possible antitumor activity. While none of the acetyl or propionyl derivatives of these amino acids and amino acid analogs caused any remarkable inhibition, certain chloroacetyl derivatives exhibited significant activity. The chloroacetyl derivatives, especially those of essential amino acids and of analogs of essential amino acids, showed modest, but pharmacologically significant, inhibition; those of nonessential amino acids exhibited no activity. When two such inhibitory acyl derivatives were combined in a single assay, the extent of inhibition was neither additive nor synergistic but was that of the more active of the two test components.

Amino Acids↗
PubMedDate not supplied

Amino acid uptake by amino acid analog resistant tobacco cell lines.

Two tobacco cell lines resistant to p-fluorophenylalanine (PFP) and one resistant to 5-methyltryptophan (5-MT) are compared with wild type cells in their ability to absorb amino acids from the medium. One p-fluorophenylalanine-resistant cell line shows greatly reduced uptake of all amino acids so is resistant to growth inhibition by other amino acid analogs. The impaired absorption is noted with amino acids, amino acid analogs and shikimate, but not with cinnamate, salicylate, nicotine, glucose, 3-O-methylglucose and palmitate. The phenylalanine transport system of the PFP-resistant cell line and the wild type both have Km values of 90 micrograms, but have different Vmax values. Several analogs of phenylalanine and several neutral L-amino acids inihibt the phenylalanine transport system, while L-aspartic acid, L-arginine, D-phenylalanine or chlorogenic acid do not interfere with the L-phenylalanine uptake. The results indicate the presence of more than one transport system for amino acid uptake. The lessened uptake of all amino acids, the specificity of the uptake systems and the unchanged binding let us conclude that a pleiotropic mutation or that some inhibitor causes the reduced uptake of all amino acids by the PFP-resistant cell line.

Amino Acids↗
PubMed1978

The stimulating effect of fatty acids and amino acid derivatives on the labellar sugar receptor of the fleshfly.

Seven D-amino acids, including D-valine, D-phenylalanine, D-leucine, D-isoleucine, D-tryptophan, D-methionine, and D-alpha-aminobutyric acid, are markedly less stimulative than the corresponding L-isomers that can stimulate the labellar sugar receptor of the fleshfly. A distinct effect of len;th of the amino acid side chain is clearly observed. Esterification and amidation of the alpha-carboxyl group, as well as substitution by hydroxyl and methyl groups, result in extremely decreased responses. Amino acids whose amino groups are located at a position other than the alpha are almost ineffective. With all these rigid stereospecificities of the sugar receptor for amino acids, certain replacement of the alpha-amino group with the hydroxyl or carbonyl group shows a slight increase of the response at neutral pH. Furthermore, certain fatty acids can stimulate the sugar receptor once the solutions are buffered at neutral pH. This observation was further supported by the presence of a remarkable similarity of stimulating effectiveness between amino acids that can stimulate the sugar receptor and those fatty acids. The similarity was shown by testing the response concentration relationships, the stimulating effect of fatty acid derivatives, the effect of treatment with p-chloromercuribenzoate, the behavioral response, and so on.

Amino Acids↗
PubMed1978

Excretion of uric acid and amino acids during diuresis in the adult female Glossina morsitans.

Radiometric analysis was carried out on the urine collected for one hour following feeding of the adult female Glossina morsitans on day 1 of a pregnancy cycle, which had previously received haemocoelic injections of U-14C labelled arginine, histidine, leucine, lysine, phenylalanine, threonine, tyrosine or valine. Mean radioactivity in the urine was quite high after labelled arginine (17.4% of injected activity) and histidine (21.8%) administration, most of the activity being in the amino acid fractions. With the remaining six labelled amino acids, mean radioactivity in the urine varied between 1.6 and 7.2% of injected activity, most of this activity occurred in a non-amino acid fraction (probably uric acid), though low radioactivity was also detected in a range of essential as well as non-essential amino acids.

Amino Acids↗
PubMed1977

Cyanide formation from histidine in Chlorella. A general reaction of aromatic amino acids catalyzed by amino acid oxidase systems.

The formation of HCN from D-histidine in Chlorella vulgaris extracts is shown to be due to the combined action of a soluble protein and a particulate component. Either horse-radish peroxidase (EC 1.11.1.7) or a metal ion with redox properties can be substituted for the particulate component. Ions of manganese and vanadium are especially effective, as are o-phenanthroline complexes of iron. Cobalt ions are less active. The D-amino acid oxidase (EC 1.4.3.3) from kidney and the L-amino acid oxidase (EC 1.4.3.2) from snake venom likewise cause HCN production from histidine when supplemented with the particulate preparation from Chlorella or with peroxidase or with a redox metal ion. The stereospecificity of the amino acid oxidase determines which of the two stereoisomers of histidine is active as an HCN precursor. Though histidine is the best substrate for HCN production, other naturally occurring aromatic amino acids (viz. tyrosine, phenylalanine and tryptophan) can also serve as HCN precursors with these enzyme systems. The relative effectiveness of each substrate varies with the amino acid oxidase enzyme and with the supplement. With respect to this latter property, the particulate preparation from Chlorella behaves more like a metal ion than like peroxidase.

Amino Acid Oxidoreductases↗
PubMed1979

Changes in plasma amino acid distribution and urine amino acids excretion during prolonged heavy exercise.

Venous plasma and urine amino acids and urea were measured in ten well-trained men, aged 23--45 years, in connection with a 70 km cross-country ski race, lasting 4.39--6.04 h, leading to slight dehydration. The estimated urea production rate during the race was of the order 7.6 mumol/min, kg b.wt, i.e. twice the rate for such men on ordinary protein intake, during ordinary activity, thus suggesting increased protein catabolism. The race led to a fall of the total plasma amino acid concentration to about 60% of the pre-race level. In particular, the branched chain amino acids (valine, iso-leucine, leucine) and alanine were markedly reduced, whereas the S-containing amino acids (taurine, cystine, methionine) and the aromatic (phenylalanine, tyrosine, trytophan, histidine) and glutamine/glutamate were increased, unchanged or only moderately reduced. It is concluded that prolonged heavy exercise is accompanied by increased protein catabolism and changes in the plasma amino acid concentrations similar to those observed during prolonged starvation, but differing from those seen at heavy exercise of less than 2 h duration or prolonged exercise of moderate intensity.

Adult↗