UMLS:C0038187 - FACTA Search

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Query: UMLS:C0038187 (starvation)
24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

L-Asparagine uptake by Stemphylium botryosum is mediated by two distinct energy- and temperature-dependent transport systems. One permease is relatively specific for L-asparagine and L-glutamine and is present in nutrient-sufficient mycelium. The specific permease shows an optimum pH at 5.2, saturation kinetics (Km = 4.4 x 10(-4) M, Vmax = 1.1 mumol/g per min), competitive gradient of L-asparagine, and higher affinity towards the L-isomer of asparagine. Amide derivatives of L-asparagine (5-diazo-4-oxo-L-norvaline or L-aspartyl hydroxamate) are the most effective competitors, alpha-amino derivative (N-acetyl asparagine) is a moderate competitor, and alpha-carboxyl derivative (L-asparagine-t-butylester) shows only slight inhibition of the specific permease. Derivatives of L-glutamine are significantly less effective competitors than those of L-asparatine. The level of the specific permease is affected by nitrogen sources and increases approximately threefold upon starvation. The nonspecific permease possesses an optimum pH at 6.8, saturation kinetics (Km = 7 x 10(-5) M, Vmax = 5 mumol/g per min, Kt = 7.4 x 10(-5) M for L-leucine), and high affinity towards various types of amino acids.
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PMID:Characterization of L-asparagine transport systems in Stemphylium botryosum. 0 27

In conditions of glucose starvation, the maximum velocity of the mediated transport of nonmetabolized and metabolized amino acids, uridine, adenosine, and sucrose across the plasma membrane is stimulated by a factor of two by the addition of 1 mM adenosine 3':5'-monophosphate to Schizosaccharomyces pombe 972h- wild strain, to the glucose-super-repressed and derepressed mutants COB5 and COB6, and to Saccharomyces cerevisiae strain IL 216-IA. The mediated uptake of 2-D-deoxyglucose and the apparently nonmediated uptake of guanosine are not stimulated by the cyclic nucleotide. N6,O2'-Dibutyryl adenosine 3':5'-monophosphate is also efficient, whereas theophylline, guanosine 3':5'-monophosphate, 5'-AMP, ATP, and adenosine are ineffective. The cellular ATP content of glycerol-grown S. pombe COB5 is about 10 nmol per mg of protein and is not decreased by further incubation in the starvation medium. The addition of 100 mM glucose markedly enhances transport without any increase of the cellular ATP content. The addition of antimycin A or Dio-9 decreases markedly both cellular ATP content and transport. The addition of 2.5 mM glucose to antimycin A-containing medium restores both transport is not necessarily of mitochondrial origin. The uptake of 2-D-deoxyglucose is unaffected by the respiratory inhibitors. Stimulation of uptake by cyclic adenosine 3':5'-monophosphate occurs only in glucose-deprived cells. The addition of 10 mM glucose elicits the disappearance of the stimulation and prevents the 30% decrease of the cellular adenosine 3':5'-monophosphate content produced by glucose starvation. Adenosine 3':5'-'monophosphate does not enhance the steady state ATP level but requires cellular ATP produced either by endogenous respiration or, in the absence of respiration blocked by antimycin A, by further addition of 2.5 mM glucose. Stimulation of active uptake by adenosine 3':5'-monophosphate does not require protein synthesis because the addition of cycloheximide or anisomycin does not prevent the stimulation of L-leucine uptake. In the absence of respiration, Dio-9, and ATPase inhibitor, suppresses instantaneously the cellular ejection of protons as well as the uptake of uridine and amino acids. It abolishes also the adenosine 3':5'-monophosphate-stimulated transport. In the presence of antimycin A, specific mitochondrial ATPase inhibitors such as venruricidin A do not inhibit metabolite uptakes and their stimulation by adenosine 3':5'-monophosphate. These results suggest that in these conditions, the target of Dio-9 is not the mitochondrial ATPase but a plasma membrane proton-translocating function generating an electrochemical gradient required for active transport. That adenosine 3':5'-monophosphate enhances the Dio-9-sensitive proton extrusion supports the view that the cyclic nucleotide might modulate the plasma membrane ATPase.
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PMID:Stimulation of active uptake of nucleosides and amino acids by cyclic adenosine 3' :5'-monophosphate in the yeast Schizosaccharomyces pombe. 16 26

We have previously shown that resistance to the beta-lactam mecillinam in Escherichia coli can be brought about by a high ppGpp pool, as observed under conditions of partial amino acid starvation and RelA-dependent induction of the stringent response. We show here that our E. coli wild-type strain, which is sensitive to mecillinam on minimal glucose plates, becomes resistant in the presence of L-leucine or L-serine (or cysteine, which inactivates the antibiotic). The resistance, which is not a transient effect and does not depend on the physiological state of the cells when plated, is specific for mecillinam and is reversed by the presence of isoleucine and valine in the medium. At least in the case of serine, the resistance is RelA-dependent. We conclude that the presence of leucine and serine in the growth medium cause partial starvation for isoleucine/valine, leading to induction of the stringent response and concomitant resistance to mecillinam.
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PMID:Leucine and serine induce mecillinam resistance in Escherichia coli. 146 98

Compounds with a reported in vivo and in vitro effect on the diabetogenicity of alloxan were studied with regard to the uptake of calcium in mouse islet mitochondria, with the aim of obtaining information on the susceptibility and selectivity of alloxan toxicity. A strong correlation was found between the uptake of calcium in mouse islet mitochondria, which is believed to be associated with the activation of oxidative enzymes involved in energy production and secretion of insulin, and the protection afforded by the injection of D-glucose, D-mannose, L-leucine and glucagon, and by the in vitro administration of cyclic AMP, L-glutamine and L-leucine. The effect of D-glucose was abolished by D-mannoheptulose. A correlation was also seen between reduced mitochondrial uptake of calcium and the potentiation of alloxan cytotoxicity afforded by 1.25-dihydroxycholecalciferol, methylene blue and menadione. The observations suggest an association between functional activity and alloxan cytotoxicity. The selectivity of the cytotoxic action of alloxan is believed to be dependent on a reduced mitochondrial uptake of calcium and an associated reduction of the energy production at low functional activity in the B-cells (e.g. in starvation which is well-known to potentiate the alloxan effect).
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PMID:Alloxan diabetogenicity: determinants of potentiation, protection and B-cell selectivity. 254 7

In submerged grown hyphae of Penicillium cyclopium the activities of seven transport systems could be distinguished which share in the uptake of L-arginine, L-glutamic acid, L-phenylalanine and L-leucine. They include the specific systems a (accepting L-arginine and L-lysine), b (L-phenylalanine, L-tyrosine), c (L-glutamic acid) and d (L-leucine), system I (a 'general amino-acid permease') and the low-affinity systems II and III, which accept acidic or basic amino acids, respectively, but also L-phenylalanine. In nutrient-sufficient cells, systems I, II and III remain repressed; uptake is dominated by the specific systems b, c, d and a, the latter reaching its maximum activity. Nitrogen starvation is the most powerful signal for the development of systems I, II and III, whereas, in carbon-starved cells, systems b, c and d reach maximum activities. The development of the general amino-acid permease in nitrogen-starved cells requires both translational and--with a few hours delay--transcriptional events as indicated by the influence of cycloheximide and 5-fluorouracil. The uptake of all amino acids is accompanied by a transient acidification of the cellular interior. Short-time preaccumulation of several anions, such as citrate, alpha-oxo-glutarate, glutamate (but not glutamine), increases the initial rate of amino-acid uptake at a pH above the optimum. Uncouplers inhibit the uptake not only under aerobic but also under anaerobic conditions, where the ATP content is not influenced by these compounds. These findings point to an H+/amino acid symport, which is tightly connected with the recycling of the incoming protons by the plasmalemma H+-ATPase.
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PMID:Kinetic properties, nutrient-dependent regulation and energy coupling of amino-acid transport systems in Penicillium cyclopium. 256 28

The occurrence of lipid metabolic changes associated with L-leucine (10 mM) stimulation of insulin release was investigated in isolated islets from either fed or starved rats. L-Leucine-stimulated secretion was potentiated by 3 mM glucose and/or 0.5 mM palmitate and was unaffected by 48 h of starvation. Islet palmitate oxidation showed a maximum rate at 3 mM glucose, and starvation increased it almost 2-fold. Regardless of the nutritional state, L-leucine strongly reduced the oxidation of palmitate and increased its incorporation into islet triacylglycerols and phospholipids at 3 mM glucose. This shift of fatty acid metabolism toward esterification might play a role in the mechanism of potentiation of the islet secretory response to L-leucine by glucose and palmitate.
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PMID:Effects of L-leucine on palmitate metabolism and insulin release by isolated islets of fed and starved rats. 352 12

The transport of the aromatic amino acids into isolated rat liver cells was studied. There was a rapid and substantial binding of the aromatic amino acids, L-alanine and L-leucine to the plasma membrane. This has important consequences for the determination of rates of transport and intracellular concentrations of the amino acids. Inhibition studies with a variety of substrates of various transport systems gave results consistent with aromatic amino acid transport being catalysed by two systems: a 2-aminobicyclo(2,2,1)heptane-2-carboxylic acid (BCH)-insensitive aromatic D- and L-amino acid-specific system, and the L-type system (BCH-sensitive). The BCH-insensitive component of transport was Na+-independent and facilitated non-concentrative transport of the aromatic amino acids; it was unaffected by culture of liver cells for 24 h, by 48 h starvation, dexamethasone phosphate or glucagon. Kinetic properties of the BCH-inhibitable component were similar to those previously reported for the L2-system in liver cells. The BCH-insensitive component was a comparatively low-Km low-Vmax. transport system that we suggest is similar to the T-transport system previously seen only in human red blood cells. The results are discussed with reference to the importance of the T- and L-systems in the control of aromatic L-amino acid degradation in the liver.
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PMID:Transport of the aromatic amino acids into isolated rat liver cells. Properties of uptake by two distinct systems. 395 48

The neutral amino acid transport systems of freshly isolated rat pancreatic islets have been studied by first examining the transport of L-alanine and the nonmetabolizable analogue 2-(methylamino)isobutyric acid (MeAIB). By comparing the uptake of MeAIB and L-alanine for their pH dependency profile, choline and Li+ substitution for Na+, tolerance to N-methylation, and competition with other amino acids, the existence in pancreatic islets of both A and ASC amino acid transport systems was established. The systems responsible for the inward transport of five natural amino acids was studied using competition analysis and Na+ dependency of uptake. These studies defined three neutral amino acid transport systems: A and ASC (Na+-dependent) and L (Na+-independent). L-Proline entered rat islet cells mainly by system A; L-leucine by the Na+-independent system L. The uptake of L-alanine, L-serine, and L-glutamine was shared by systems ASC and L, the participation of system A being negligible for these three amino acids. An especially broad substrate specificity for systems L and ASC is therefore suggested for the rat pancreatic islet cells. The regulation of amino acid transport was also investigated in two conditions differing as to glucose concentration and/or availability, i.e. islets from fasted rats and islets maintained in tissue culture at high or low glucose concentrations. Neither alanine nor MeAIB transport was altered by fasting of the islet-donor rats. On the other hand, pancreatic islets maintained for 2 days in tissue culture at high (16.7 mM) glucose transported MeAIB at twice the rate of islets maintained at low (2.8 mM) glucose. Amino acid starvation of pancreatic islets during 11 h of tissue culture resulted in a 2-fold increase in MeAIB transport.
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PMID:Neutral amino acid transport in isolated rat pancreatic islets. 635 18

1. Rates of appearance and oxidation of plasma L-leucine, L-phenylalanine and L-tyrosine, as well as conversion of plasma phenylalanine into plasma tyrosine, were determined in 90-120 g rats after overnight starvation and while receiving 115-120 mumol of L-phenylalanine/h. 2. In the post-absorptive state, plasma tyrosine and phenylalanine appearances were similar, despite the fact that 22% of plasma tyrosine appearance could be attributed to the hydroxylation of phenylalanine. 3. A constant infusion of 115-120 mumol of L-phenylalanine/h did not significantly alter plasma leucine kinetics, but increased appearance of plasma phenylalanine and tyrosine. The percentage of phenylalanine and tyrosine appearance that was oxidized increased from 12.1% and 24.4% to 37.3% and 48.0% respectively. In phenylalanine-loaded rats, 72% of plasma tyrosine appearance could be attributed to the conversion of phenylalanine. 4. Whole-body tyrosine oxidation measured from a continuous infusion of either L-[14C]tyrosine or L-[14C]phenylalanine differed by 165%. 5. It can be concluded that, in the post-absorptive state, phenylalanine hydroxylation makes a substantial contribution to the plasma appearance of tyrosine and is significantly increased when phenylalanine is administered. The disposal of excess infused phenylalanine is a result of a greater percentage of plasma phenylalanine being converted into tyrosine and a greater proportion of tyrosine being further oxidized. However, apparent tyrosine oxidation rates estimated from plasma tyrosine specific radioactivities and appearance of expired 14CO2 during administration of [14C]tyrosine are underestimates of true rates, in part because tyrosine generated from phenylalanine hydroxylation is catabolized without freely equilibrating with the plasma compartment.
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PMID:The contribution of phenylalanine to tyrosine metabolism in vivo. Studies in the post-absorptive and phenylalanine-loaded rat. 687 Aug 7

Cell growth of Saccharomyces cerevisiae ATCC 12341 inhibited by the antibiotic cerulenin, a specific inhibitor of fatty acid synthesis, was restored by oleic acid (18 : 1) to give saturated fatty acid-starved cells, which could not grow when again transferred into a fresh synthetic medium containing the antibiotic and oleic acid. The growth of the saturated fatty acid-starved cells was restored when they were transferred into a medium supplemented with myristic acid (14 : 0), pentadecanoic acid (15 : 0), and palmitic acid (16 : 0) in the presence of cerulenin and oleic acid. Cellular saturated fatty acid content in the growth-restored cells was also restored to about two-thirds of that of the normal yeast cells. The DNA, RNA, and cell wall synthetic capabilities of the saturated fatty acid-starved cells were almost normal, but the L-leucine uptake and cytochrome pattern were severely impaired. These impairments were reversed on supplying palmitic acid. The decrease of L-leucine uptake of the yeasts was also caused by the addition of cerulenin alone. However, since the decrease occurred later than the inhibition of fatty acid synthesis, it was considered to be a secondary effect. These results, obtained by using the saturated fatty acid-starved cells, indicate that the membranes of S. cerevisiae require certain amounts of saturated fatty acid and that the membrane functions (energy metabolism, transport, and so on) are impaired by starvation of saturated fatty acids.
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PMID:Saturated fatty acid-starved cells of Saccharomyces cerevisiae grown in the presence of cerulenin and oleic acid. 701 49

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