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

1. The occurrence and characterization of acidic amino acid transport in the plasma membrane of a variety of cells and tissues of a number of organisms is reviewed. 2. Several cell types, especially in brain, possess both high- and low-affinity transport systems for acidic amino acids. 3. High-affinity systems in brain may function to remove neurotransmitter amino acid from the extracellular environment. 4. Many cell systems for acidic amino acid transport are energized by an inwardly directed Na+ gradient. Moreover, certain cell types, such as rat brain neurons, human placental trophoblast and rabbit and rat kidney cortex epithelium, respond to an outwardly directed K+ gradient as an additional source of energization. This simultaneous action may account for the high accumulation ratios seen with acidic amino acids. 5. Rabbit kidney has been found to have a glutamate-H+ co-transport system which is subject to stimulation by protons in the medium. 6. Acidic amino acid transport in rat brain neurons occurs with a stoichiometric coupling of 1 mol of amino acid to 2 mol of Na+. For rabbit intestine, one Na+ is predicted to migrate for each mol of amino acid. 7. Uptake in rat kidney cortex and in high-K+ dog erythrocytes is electrogenic. However, uptake in rabbit and newt kidney and in rat and rabbit intestine is electroneutral. 8. Na+-independent acidic amino acid transport systems have been described in the mouse lymphocyte, the human fibroblast, the mouse Ehrlich cell and in rat hepatoma cells. 9. In a number of cell systems, D-acidic amino acids have substantial affinity for transport; D-glutamate, in a number of systems, however, appears to have little reactivity. 10. Acidic amino acid transport in some cell systems appears to occur via the "classical" routes (Christensen, Adv. Enzymol. Relat. Areas Mol. Biol. 49, 41-101, 1979). For example, uptake in the Ehrlich cell is partitioned between the Na+-dependent A system (which transports a wide spectrum of neutral amino acids), the Na+-dependent ASC system (which transports alanine, serine, threonine, homoserine, etc.), and the Na+-independent L system (which shows reactivity centering around neutral amino acids such as leucine and phenylalanine). Also, a minor component of uptake in mouse lymphocytes occurs by a route resembling the A system. 11. Human fibroblasts possess a Na+-independent adaptive transport system for cystine and glutamate that is enhanced in activity by cystine starvation.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Acidic amino acid transport in animal cells and tissues. 330 25

Fibroblasts increase the catabolism of certain intracellular proteins in response to serum withdrawal, and these proteins contain specific peptide regions that may be required for their increased degradation. We show that the increased degradation of microinjected ribonuclease A during serum withdrawal can be blocked by co-injection of a pentapeptide corresponding to residues 7-11 of ribonuclease A, Lys-Phe-Glu-Arg-Gln. Furthermore, similar peptide sequences appear to play a widespread role in targeting proteins for enhanced degradation. Affinity-purified antibodies raised against the pentapeptide are able to precipitate 20-35% of radiolabeled cytosolic proteins from fibroblasts. Such proteins are preferentially degraded when cells are deprived of serum while nonimmunoprecipitable proteins are degraded at the same rate in the presence and absence of serum. Immunoreactive cytosolic proteins also exist in rat liver and kidney, and these proteins are depleted when protein degradation rates are enhanced due to starvation. Several types of evidence suggest that the peptides recognized in cellular proteins are similar to Lys-Phe-Glu-Arg-Gln but are not this exact sequence. Analyses of amino acid sequences for four proteins whose degradative rates are enhanced in response to serum withdrawal and for four proteins that are degraded in a serum-independent manner indicate two possible peptide motifs related to Lys-Phe-Glu-Arg-Gln that may target cellular proteins for enhanced degradation. These results, combined with previous studies (McElligott, M. A., Miao, P., and Dice, J. F. (1985) J. Biol. Chem. 260, 11986-11993), suggest that these peptide regions target specific proteins to a lysosomal pathway of degradation during serum withdrawal.
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PMID:Peptide sequences that target proteins for enhanced degradation during serum withdrawal. 336 Aug 7

The bulk of cellular protein in hepatocytes is sequestered and degraded by two classes of autophagy, (a) an overt or macro form, and (b) microautophagy. Macroautophagy is rapidly induced by amino acid deprivation and the administration of glucagon and suppressed by amino acids and insulin. Amino acids appear to be its primary regulator since liver perfusion studies have shown that it can be inhibited almost completely and proteolysis decreased from maximal (4.5% hr) to basal rates (1.7%/hr) by 4 times normal plasma amino acid concentrations. The resulting alterations in the aggregate volume of autophagic vacuoles are associated with proportional changes in the amount of cytoplasmic protein sequestered and in rates of protein degradation. Since the apparent turnover of autophagic vacuoles is 0.087 min-1, the pools of sequestered protein at all levels of macroautophagic stimulation are sufficient to account fully for the observed rates of accelerated rate of proteolysis. Microautophagy differs from the former in that the cytoplasmic 'bite' is smaller and it is not subject to acute physiological regulation. It is, however, dramatically decreased to near zero during refeeding after prior starvation. These and other findings indicate that it is adaptively regulated, possibly as a consequence of alterations in the amount of smooth endoplasmic reticulum. The amino acid control of accelerated protein degradation appears to involve direct inhibition by a small group of amino acids (Leu, Tyr/Phe, Gln, Pro, Met, Trp, and His) and the permissive action of alanine. Of unusual interest is the fact that, whereas the inhibitory amino acid group evokes responses identical to a complete amino acid mixture at 0.5x and 4x normal amino acid concentrations, it loses its effectiveness at normal levels; similar responses have been shown for leucine alone. The loss of effectiveness at normal concentrations is abolished by the addition of 0.5 mM alanine which by itself is not directly inhibitory. No other amino acid can replace alanine. These findings suggest a novel role for alanine that could be of importance in linking energy demands to proteolysis. A hypothetical model for proteolytic regulation by leucine and the other inhibitory amino acids is presented.
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PMID:The lysosomal pathway of intracellular proteolysis in liver: regulation by amino acids. 349 68

Fibroblasts from normal adult forearm skin and neonatal foreskin were cultured and examined for their ability to synthesize and secrete elastase and neutral cathepsin. All of the cultures examined produced detectable amounts of elastase using insoluble elastin as substrate. An enzyme was also found that hydrolyzed the synthetic elastin substrate, N-succinyl-(Ala)3-p-nitroanilide, but did not degrade insoluble elastin. In addition, activity against the synthetic cathepsin substrate N-benzoyl-DL-phenylalanine-naphthyl ester was found. Inhibitor profiles indicate that the elastin and N-succinyl-(Ala)3-p-nitroanilide degrading activities are due to metalloproteinases. Degradation of N-benzoyl-DL-phenylalanine-naphthyl ester can be inhibited by phenylmethylsulfonyl fluoride. These proteinases were usually found associated with the cell layer. Although activities of the measured proteinases were detected in all cultures, increased or decreased enzyme activities were not predictably related to passage number or length of serum starvation. Degree of confluence also affected proteinase activities. Separation of the dermal-epidermal junction can be produced by the injection of these proteinases into intact mouse skin.
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PMID:Elastase and neutral cathepsin production by human fibroblasts: effect of culture conditions on synthesis and secretion. 352 5

An isotope-dilution method is described for the measurement of N tau-methylhistidine release from the perfused rat heart. We argue that release of N tau-methylhistidine is indicative of cardiac actin degradation. N tau-Methylhistidine release is compared with phenylalanine release in the presence of cycloheximide (phenylalanine release being a measure of degradation of mixed proteins). In hearts perfused with glucose plus acetate, the rate of actin degradation was increased by starvation and was not inhibited by insulin. In contrast, the rate of mixed-protein degradation was decreased by starvation and was inhibited by insulin. The fractional rate of degradation of mixed proteins in hearts from fed or starved rats was greater than that for actin. It is suggested that there are at least two pools of intracellular protein, the degradation rates of which differ in terms of their response to insulin and starvation.
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PMID:Contrasting response of protein degradation to starvation and insulin as measured by release of N tau-methylhistidine or phenylalanine from the perfused rat heart. 354 99

Concentrations of free amino acids were measured in human milk and arterial blood from lactating women after an overnight fast or after a controlled breakfast. The concentrations of many free amino acids in milk (except L-tyrosine, L-aspartate, L-asparagine, L-glutamate and L-glutamine) were lower after an overnight fast than after breakfast. Similarly, the arterial concentrations of amino acids were lower except for L-asparagine, L-alanine, L-tyrosine and L-phenylalanine. Net uptake of amino acids by the mammary gland of the lactating rat was significantly lower after starvation for 6 or 24 h than in the fed state because the arteriovenous differences of amino acids and the blood flow were significantly lowered. Starvation produced a significant decrease of 2-amino-[1-14C]isobutyric acid uptake by isolated acini from lactating rat. These results show that short-term starvation decreases the amino acid supply and transport in mammary gland as well as the free amino acid concentration in milk.
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PMID:Effect of fasting on amino acid metabolism by lactating mammary gland: studies in women and rats. 357 66

Determination of protein synthesis in individual tissues is important to understand the changes in protein metabolism during catabolic states. Three methods based on different underlying assumptions were compared in assessing muscle protein synthesis during nutritional manipulation. Rats were nonstarved, starved for 1 or 3 days, or refed for 2 days after 3 days of starvation. The extensor digitorum longus (EDL) muscles from the two hindlegs were used for analysis. In one EDL muscle the concentration and size distribution of ribosomes as well as the incorporation of [14C]leucine into protein in a cell-free system were determined. The other EDL muscle was incubated as such and the incorporation of [14C]phenylalanine into protein was measured. The total ribosome concentration per milligram of DNA decreased to 65% on the third day of starvation and remained low after refeeding. The amount of polyribosomes in the percentage of total ribosomes fell to 90% on the first day of starvation, regained the initial level on the third day, and reached 110% upon refeeding. During refeeding amino acid incorporation into protein in a cell-free system decreased to 40% and that in intact muscle to 64% of the prestarvation level. Upon refeeding, the activity increased to or above the original values. The use of several different techniques in parallel to assess protein synthesis in skeletal muscle is recommended since it gives information about the factors involved in regulation of the translational process in intact mammalian tissues.
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PMID:Protein synthesis in skeletal muscle of rats following starvation and refeeding. 365 37

Starvation of the mouse hepatoma cell line Hepa for an essential amino acid (Trp, His, Leu, Ile or Phe) stimulated the incorporation of [3H]adenosine as ADP-ribose monomer into an 80,000-Mr protein, P80. Two-dimensional electrophoresis of Hepa proteins showed that P80 was the only protein labeled under starvation conditions. Time course experiments showed that the ADP-ribosylation of P80 was a consequence rather than the cause of reduced translational activity. Cycloheximide treatment and incubation at reduced temperatures also reduced the rate of protein synthesis and stimulated the ADP-ribosylation of P80. Starvation-dependent ADP-ribosylation of P80 was shown to occur in three other cell lines (Chang, Neuro-2a, and chick comb fibroblasts).
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PMID:Translational control of ADP-ribosylation in eucaryotic cells. 379 12

The effects of maternal starvation upon protein turnover in various tissues of the fetal rat were determined. Protein synthesis was determined in fetal tissues by the intravenous injection of "massive" amounts of 3H-phenylalanine into the maternal circulation, followed by measurements of tissue free and protein-bound phe specific radioactivity in fetal diaphragm, heart, liver, and brain. Rates of protein degradation in fetal tissues were assessed by subtracting protein accretion rates from protein synthesis. Fractional rates of protein synthesis were minimally affected by maternal starvation in diaphragm, heart, and brain. The major factor contributing to reduced fetal protein accretion in these fetal tissues during maternal starvation was enhanced protein breakdown. These findings differ from those previously reported in young adult rodents following fasting or malnutrition.
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PMID:Protein turnover in tissues of the rat fetus following maternal starvation. 379 16

To evaluate whether the alterations in amino acid (AA) metabolism that follow the lambda-carrageenan injury are direct consequences of wounding and are therefore independent of food intake, plasma AA, in vivo muscle intracellular free AA, and AA release during isolated hindlimb perfusions were determined in pentobarbital-anesthetized rats with lambda-carrageenan-induced hindlimb muscle wounds (W) and in pair-fed (PFC) and ad libitum-fed (ALC) non-wounded controls. Both PFC and W animals showed different plasma and muscle intracellular AA composition that ALC. The alterations observed in these compartments in W animals may not have resulted exclusively as a consequence of the wound. Wounded hindlimbs released more AA during perfusion than either control group. The marked increase in net protein catabolism of W muscle appeared to be related to wounding and not a consequence of partial starvation. The normalized release (amino acid/phenylalanine ratio) of glutamine (W less than ALC), alanine (W less than PFC and ALC), and the branched-chain amino acids (W greater than PFC and ALC) differed among groups, suggesting an alteration in the metabolism of these AA in W tissue.
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PMID:Amino acid metabolism after lambda-carrageenan injury to rat skeletal muscle. 394 10


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