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

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.
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PMID:Derepression of amino acid transport by amino acid starvation in rat hepatoma cells. 1 7

When treated with chloramphenicol, Escherichia coli 15T minus produces two new species (IV and V) of transfer ribonucleic acid specific for phenylalanine in addition to the major normal species (II) and two minor normal species (I and III), which are seen as distinct components upon fractionation by chromatography on columns of benzoylated diethylaminoethyl-cellulose. Species IV is produced when cells are grown in iron-deficient medium and is, therefore, probably deficient in the 2-methylthio modification of N-6-(delta-2-isopentenyl) adenosine. A new minor species (Va) also appears under those conditions. All of the new components elute earlier than the major normal species. Addition of chloramphenicol to iron-deficient cells leads to the production of species V, and that production is blocked by rifampin, as is the production of species IV. Thus, species IV and V appear to be transcriptional products. Although E. coli 15T minus appears to be rel plus, starvation for methionine or cysteine leads to the accumulation of species IV (without addition of chloramphenicol); rifampin blocks the accumulation. Species V is still produced on addition of chloramphenicol to starved cultures. Starvation for arginine or tryptophan does not alter the chromatographic profile from the normal case. Treatment with permanganate indicates that species II and IV contain isopentenyladenosine but that species V does not. Species V appears to be deficient in both isopentenyl and methylthio modifications of adenosine and perhaps at least one other modification, because removing the isopentenyl moiety from adenosine does not convert species IV into species V, but converts it into species Va. A precursor relationship among species V, VI, and II is suggested by following the chromatographic profile of phenylalanine transfer ribonucleic acid during recovery of E. coli from treatment with chloramphenicol; the various species increase and decrease in a sequential manner.
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PMID:Precursor relationship of phenylalanine transfer ribonucleic acid from Escherichia coli treated with chloramphenicol or starved for iron, methionine, or cysteine. 4 64

A study was made of the transport of a variety of amino acids by uninfected and Rous sarcoma virus-infected chicken embryo fibroblasts. Following a period of amino acid starvation, transformed, but not normal cells, showed increased levels of transport for alpha-aminoisobutyric acid, proline and alanine, three amino acids which are transported primarily by the A transport system. There was no starvation-induced increase in the transport of leucine, phenylalanine, lysine, or cycloleucine. In the absence of starvation, normal and transformed cells exhibited comparable rates of amino acid transport. Cycloheximide was able to block the increase in uptake. The enhanced uptake was characterized by an increase in Vmax for transport and little change in Km. The data demonstrate that an alteration in the regulation of the A amino acid transport system is an early event in malignant transformation by Rous sarcoma virus. However, since this alteration in made manifest only following a period of starvation, our findings suggest that increased amino acid uptake does not play a role in generating the other manifestations of the transformed state seen in cell culture.
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PMID:Amino acid transport in normal and Rous sarcoma virus-transformed chicken embryo fibroblasts. 22 76

The structures of the major, chromatographically unique phenylalanine and leucine tRNAs produced during leucine starvation of a relaxed control (rel-) mutant of E. coli have been determined. The results demonstrate that the unique species are modification-deficient forms of the major, normally occurring isoacceptor species. The unique tRNAphe differs from the fully modified species at nucleotide positions 16, 37, 39, 47, and 55 from the 5' terminus. The unique species contains uridine (U) in place of dihydrouridine-16 (D16), isopentenyladenosine in place of 2-thiomethyl-N6-(delta2-isopentenyl)adenosine-37, a mixture of U and pseudouridine (psi) in position 39, a mixture of U and 3-(3-carboxypropyl)uridine at position 47, and a mixture of U and psi at position 55. The chromatographically normal isoacceptor from amino acid starved cells is deficient in D16 and psi55, indicating that that species is a mixture of mature and undermodified tRNAs. The unique tRNALeu isoacceptor consists of two subspecies which are undermodified forms of the major, normally occurring isoacceptor, tRNALeuI. Both unique subspecies lack the D and psi residues which occur at positions 16 and 39 from the 5' terminus; one subspecies also lacks D17. Compared with the tRNALeusI from wild-type strains of E. coli B and K12, both tRNALeuI from nonstarved cells and the unique, rel-tRNALeu are deficient in the modified guanosine which normally occurs adjacent to the anticodon and the pseudouridine in the GTpsiC sequence of the psi loop. Both the unique tRNAPhe and the unique tRNALeu lack dihydrouridine residues which occur in the 5' half of the D loop and pseudouridines which occur in the 3' half of the anticodon loop and adjoining stem. Taken together, these findings suggest that the same enzymes are responsible for the formation of these particular modified bases in both tRNAs. The results further suggest that several, perhaps most, of the tRNAs from cells cultured under conditions in which RNA and protein synthesis are uncoupled will be similarly deficient in dihydrouridine and pseudouridine and other minor nucleosides which occur less frequently. Because both modification-deficient rel-tRNAs have dihydrouridine at position 20 and pseudouridine in the psi loop (and at position 41 in the unique tRNALeu), the results support the view that there was multiple D-and psi-forming enzymes in E. coli, some of which may turn over rapidly or are selectively inactivated when protein synthesis is blocked. The results are discussed with a view toward understanding the structural basis for the altered biological activity of the unique tRNAPhe species and the order of events in the posttranscriptional modification of newly synthesized tRNA.
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PMID:Modification-deficient transfer ribonucleic acids from relaxed control Escherichia coli: structures of the major undermodified phenylalanine and leucine transfer RNAs produced during leucine starvation. 32 16

A translation of polyU in a cell-free system from CP78 (relA+) and CP79 (relA-) E. coli strains is investigated. The strains studied no not differ in misreading at Mg2+ concentration of 20 mM and concentrations of 16 mM (optimal for phenylalanine incorporation) and 18-22 mM (optimal for leucine incorporation) respectively. It is found that leucine incorporation increases similarly in both strains under conditions simulating an amino acid deficience (in phenylalanine-free incubation medium): the ratio leucine(-phenylalanine)/leucine (+phenylalanine) is 3.5-4 at a concentration of enzymatic fraction protein being 15-30 mkg per example, and it is 2 st a concentration of enzymatic fraction of 60-180 mkg of protein. It is suggested that differences in activities of a number of enzymes under amino acid starvation in Rel+ and Rel- cells are not due to differences in the precision of mRNA translation, but depend on the activity of respective genes.
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PMID:[Translation of poly U by ribosomes from rel+ and rel- E. coli strains]. 34 96

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.
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PMID:Changes in plasma amino acid distribution and urine amino acids excretion during prolonged heavy exercise. 52 87

The amino acid pattern following total hip replacement is characterized by increases in muscle of the branched chain amino acids (leucine, isoleucine and valine), the aromatics (phenylalanine and tyrosine) as well as methionine. The nonessential amino acids in muscle tend to decline, glutamine having the most marked change. Plasma levels of the essential amino acids increase while the nonessentials tend to decrease. This pattern differs from that observed in other catabolic states (uremia, starvation, untreated diabetes) and is significantly different from the effects of inactivity and starvation combined. This suggests that injury can be characterized by a unique pattern of muscle and plasma amino acids.
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PMID:Muscle and plasma amino acids after injury: the role of inactivity. 73 57

Inhibition of protein synthesis in relaxed control E. coli results in the formation of chromatographically unique isoacceptor species of phenylalanine tRNA. The genetic origin and some functional properties of the major unique species of tRNA (Phe) produced during leucine starvation were investigated. RNA:DNA hybridization analyses revealed that the normally occurring and major unique species of tRNA (Phe) are generated from DNA sequences which are identical or closely related and that there may be only one such sequence in the E. coli chromosome. Results from 32P pulse-chase experiments revealed that the unique tRNA (Phe) can be converted to a chromatographically normal form upon resumption of cell growth in fully supplemented medium. These findings, taken with earlier results which indicate that the unique species is not derived from preexisting, normally occurring species, indicate that the unique tRNA(Phe) is a modification-deficient form of the normal species. Comparative studies of the unique and normal phenylalanine tRNAs revealed that the unique species is aminoacylated at a much lower rate than the normal species and is only about 60% as efficient in a tRNA-dependent, poly(U)-directed protein synthesizing system.
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PMID:Unique phenylalanine transfer ribonucleic acids in relaxed control Escherichia coli: genetic origin and some functional properties. 77 26

Three bands of hydrolytic activity toward the chromogenic protease substrate N-acetyl-DL-phenylalanine beta-naphthyl ester (NAPNE) can be observed after gel electrophoresis of crude extracts of Salmonella typhimurium or Escherichia coli. Mutants deficient in one of these three activities have been isolated using a staining procedure that identifies colonies that show reduced ability to hydrolyze NAPNE. These mutants lack the strongest of the three bands of activity. The Salmonella mutations (designated apeA) are all co-transducible with purE, and the order (pro)-apeA-Hfr K17 origin-purE has been established. Strains carrying apeA mutations have wild-type doubling times. None of the apeA mutants isolated gains an auxotrophic requirement as a result of loss of the apeA gene product. The rates and extents of protein degradation during starvation for a carbon source or during growth after exposure to the amino acid analogue canavanine do not seem to be affected by apeA mutations. Revertants of apeA mutations (selected by screening for clones that have regained the ability to hydrolyze NAPNE) frequently contain a new enzymatic activity not found in wild-type cells.
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PMID:Mutants of Salmonella typhimurium deficient in an endoprotease. 77 37

The heterogeneity of undermodified phenylalanine tRNA produced in relaxed control E. coli during amino acid starvation was investigated. Examination of the RPC-5 elution profiles of tRNAPhe prepared from non-starved cells and cells starved of a variety of amino acids, including some known to be involved in the formation of modified bases revealed that: (1) only one species of fully modified tRNAPhe appears to occur in cells grown in enriched medium; (2) at least two chromatographically unique isoacceptor species are observed in addition to the normal tRNAPhe in starved cells; (3) the unique, undermodified species of tRNAPhe from leucine-starved cells, known to be deficient in dihydrouridine, pseudouridine, 2-thiomethyl-N6-(delta2-isopentenyl) adenosine and 3-(3-amino-3-carboxypropyl) uridine, co-elute with the unique species produced in cells starved of histidine or arginine or treated with puromycin or chloramphenicol; (4) additional unique species of tRNAPhe can be detected in methyl- and sulfur-deficient tRNA from methionine- and cysteine-starved cells; (5) analysis of phenoxyacetylated tRNA revealed that the chromatographically unique and normal species from starved cells contain subspecies deficient in 3-(3-amino-3-carboxypropyl) uridine; and (6) using phenoxyacetylation as a means of effecting the resolution of undermodified subspecies, a total of at least ten chromatographically unique subspecies of rRNAPhe were detected in an organism that appears to posses only one gene for tRNAPhe. Taken together, the results support the view that there are both general and specific effects of amino acid starvation on the post-transcriptional modification of tRNA.
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PMID:General and specific effects of amino acid starvation on the formation of undermodified Escherichia coli phenylalanine tRNA. 79 74


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