Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Each medium renewal of confluent primary heart cell cultures derived from new born rats induces a pleiotypic response which leads to active proliferation. The presence of serum in the culture medium is essential for this activation of growth. Nutrient starvation prior to the activation decreases the response of the cells to serum. Serum starvation prior to the activation increases the serum dependence of the incorporation of labelled leucine but leaves the serum dependence of DNA synthesis unchanged. Ageing in culture decreases the serum dependence of the incorporation of labelled thymidine and amino acids but maintains it for alpha amino isobutyric acid transport. Several active components in human serum were distinguished by fractionated dialysis. A single dialyzable component stimulates both thymidine and amino acid incorporations. The transport of 2 deoxy-D-glucose is activated by another rapidly dialyzing component. The activation of alpha amino isobutyric acid transport may result from several components that are distanct from the previous ones. These results imply that a multiplicity of controls underly the pleiotypic activation of heart cell cultures by medium changes.
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PMID:The growth of heart cells in culture. Evidences for a multiple activation of the pleiotypic program. 71 43

Distribution ratios (intracellular concn/extracellular concn) of alpha-amino isobutyric acid (AIB) after intravenous injection were determined in fed, 12-h, 1-day, and 5-day starved rats. Progressive increases (over fourfold) in the distribution ratios of AIB in the liver and progressive decreases (over threefold) in the gastrocnemius muscle occurred within these periods. On full day of protein deprivation was without effect on AIB distribution ratios, but after 5 days it produced an increased distribution ratio of AIB in the liver (twofold), without affecting that of the muscle. A sudden increase in hepatic glucose output, induced by phlorizin, was followed by an increase in the liver distribution ratio of AIB. In starvation the increase in plasma concentration of glucagon and decrease in insulin level preceded the changes in AIB distribution ratios; in protein deprivation there was no change in plasma concentrations of these hormones. It is concluded that caloric restriction profoundly affects amino acid transport by the liver and by the skeletal muscle. These transport changes would enhance the availability of substrates for increased gluconeogenesis during starvation.
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PMID:Dietary regulation of liver and muscle transport of amino acid. 125 99

Maternal smoking depressed the active uptake of amino acids by human placentae and lowered their levels in the placenta and umbilical vein. During starvation of cells for amino acids, more amino acid carriers are induced and incorporated into the plasma membrane. A question arises whether there could be similar changes due to maternal smoking in the placental amino acid uptake carrier systems. Therefore, the characteristics of (a) the uptake of 2-amino[I-14C]-isobutyric acid (AIB) by isolated placental villi, (b) gammaglutamyltranspeptidase (GGTP), a critical enzyme of the gammaglutamyl cycle (GGC) for the uptake of amino acids in human placenta, and (c) lipid structural parameters (reciprocal of fluidity), by steady state fluorescence polarization of plasma membrane vesicles of microvilli (MV) and microsomal membranes (MM) of umbilical and chorionic plate arteries of placentae of smoking and non-smoking mothers were investigated. The above investigations gave the following results: (a) Washed placental villi of smokers exhibited higher capacity for AIB uptake than those of non-smokers. The higher uptake capacity was mainly due to increase in Vmax for AIB uptake in smokers. Km increased for placental AIB uptake in smokers. (b) Maternal smoking lowered GGTP activity of MV by decreasing its Vmax. Therefore, maternal smoking decreases the formation of gammaglutamyl-amino acid (GGAA) on the surface of trophoblast which are absorbed by the trophoblast. The degree of absorption of GGAA is considered as an inverse environmental signal for the cell to regulate amino acid transport systems. Maternal smoking seems to decrease the formation and absorption of GGAA and thereby induce the formation of new carriers for AIB uptake. (c) Maternal smoking increased the values for lipid structural order parameters and microviscosity of MV and induced tolerance against fluidization by ethyl alcohol in MM of umbilical and chorionic arteries. The alterations could increase Km for AIB uptake system and decrease the sensitivity of umbilical and chorionic arteries to vasoconstrictive substances like 5-hydroxytryptamine and catecholamine which are released by nicotine. All these changes tend to overcome the deficits produced in placental amino acid transport and satisfy the demands of the growing fetus for amino acids.
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PMID:Maternal tobacco smoking and changes in amino acid uptake by human placental villi: induction of uptake systems, gammaglutamyltranspeptidase and membrane fluidity. 257 Nov 46

Significant increase in the activity of an acetyl-CoA hydrolase (ATP-stimulated, ADP-inhibited enzyme) in the supernatant fraction of rat liver was observed after 44-68 h of starvation (about 2-fold), and in the early stage of diabetes (about 1.6-fold), but not in the chronic stage of diabetes. The increased enzymatic activity in starved rats returned to the control level within 20 h when the animals were given laboratory chow, but not when they were given fat-free diet with a high carbohydrate content, and the enzyme activity was increased by the latter diet containing 1% thyroid powder. A single intraperitoneal injection of 3,3'5-triiodo-L-thyronine or 3,3',5,5'-tetraiodo-L-thyronine resulted in twice the normal enzyme activity two days later, and conversely 7 days after thyroidectomy, the enzyme activity was about 60% of the control level. A single subcutaneous injection of alpha-(p-chlorophenoxy)isobutyric acid, a hypolipidemic drug, doubled the enzyme activity in euthyroid rats, but not in thyroidectomized rats. Of the various tissues tested besides the liver, only the kidney had detectable ATP-stimulated and ADP-inhibited enzyme activity (5% of the activity in liver cytosol). The kidney enzyme had similar kinetic and immunochemical properties to the liver enzyme. Changes in the enzyme activity in the liver in various states were closely related to the amount of enzyme present, judging from results obtained by enzyme-linked immunosorbent assay. The physiological role of this enzyme (which hydrolyzes acetyl-CoA to acetate and CoASH) may be in maintenance of the cytosolic acetyl-CoA concentration and CoASH pool for both fatty acid synthesis and oxidation.
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PMID:Physiological changes in the activities of extramitochondrial acetyl-CoA hydrolase in the liver of rats under various metabolic conditions. 286 34

The effect of amino acid depletion or supplementation and the effect of glucagon and insulin on the amino acid transport mediated by system A were investigated by determining the uptake of either 2-amino [1-14C]isobutyric acid (AIB) or N-methyl 2-amino [1-14C]isobutyric acid (MeAIB) in rat hepatocytes, freshly isolated at different stages of pre- and postnatal development. The data obtained show that the Na+-dependent uptake was higher at the earliest developmental stages, and steadily decreased until the adult level. The hormones increased AlB and MeAIB uptake enhancing the Vmax, while the Km was unchanged. This effect was evident in cells from adult and 18-20-day-old fetuses, while no response was present before the 18th day of fetal life and in the perinatal period. Actinomycin D or cycloheximide abolished this hormone-dependent increase. A decrease in AlB and MeAIB transport after incubation in an amino acid-rich medium was demonstrated at all ages tested, but was particularly evident in the prenatal life. The increase in the activity of the system following amino acid starvation was shown to be mostly dependent from de novo protein synthesis in the fetal life; on the contrary in the adult the increase appeared to be more linked to the release from transinhibition of the transport.
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PMID:Regulation of amino acid transport in isolated rat hepatocytes during development. 302 4

When amino acids that are generally transported through the A system are added to derepressed cultures of CHO-K1 cells or to cultures that are undergoing starvation-derepression, as in the co-repressor (co-r), co-inactivator (co-i), (co-ri) assay, the A system undergoes trans-inhibition, inactivation, and repression. The effect of inactivation and repression is not related to the ability of amino acids to bind to the A system transporter but supports a model in which these amino acids act as co-r's/co-i's, and by binding to a aporepressor/inactivator (apo-ri), the product of gene R1, convert it into a repressor/inactivator (ri). For example, beta-alanine acts as a strong co-r but does not inhibit proline transport through the A system. Hydroxyproline and histidine, although poor inhibitors of proline transport, are very effective as co-ri's. Diaminobutyrate, phenylalanine, alpha-keto-glutarate, pyro-glutamate, isoleucine, and valine, compounds that inhibit A system transport, listed in decreasing order of effectiveness, are all equally poor as co-ri's. Also the Km for the transport of 2-(methylamino)isobutyric acid (MeAIB) through the A system is two times the concentration of MeAIB required to produce one-half inactivation. Amino acid effectors and mutation can modify the conversion of the apo-ri to repressor (r) and inactivator (i). The apo-ri is converted by alanine, serine, proline, and MeAIB to ri, by beta-alanine and tryptophane to r, and by hydroxyproline to r and reduced i. The full constitutive and partial constitutive mutants alar4 and alar2, respectively, are in the same complementation group. Alar4 has no active apo-ri while the rate of derepression of alar2 is twice and the inactivation rate is equal to that of the parent culture.
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PMID:Regulation of the A system of amino acid transport in Chinese hamster ovary cells, CHO-K1: the difference in specificity between the apo-repressor inactivator (apo-ri) and the transporter and the characterization of the proposed apo-ri. 308 25

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

When mammalian cells are starved for amino acids, the activity of the A amino acid transport system increases, a phenomenon called adaptive regulation. We have examined the effects of those factors which support Madin-Darby canine kidney (MDCK) cell growth in a defined medium on the derepression of System A activity. Of the five factors which supported MDCK cell growth, insulin was found to be an absolute requirement for derepression. In contrast, PGE1 was a negative controlling factor for the transport system. Growth of MDCK cells in the absence of PGE1 resulted in elevated System A activity which derepressed poorly upon amino acid starvation. Kinetic analysis of alpha-(methylamino) isobutyric acid (mAIB) uptake as a function of substrate concentration showed that the elevated A activity observed when cells were grown in the absence of PGE1 was kinetically similar to the activity induced by starvation for amino acids. Transport of mAIB by amino-acid-fed cells grown in the presence of PGE1 was characterized by a linear Eadie-Hofstee graph and by a relatively low Vmax. Transport by cells starved for amino acids or by cells grown in the absence of PGE1 was characterized by biphasic kinetics for mAIB transport and by elevated Vmax values. An influence of growth factors on the inactivation of derepressed A activity was also observed. In the presence of cycloheximide the rate of loss of A activity in amino-acid-starved cells was 1/4-1/2 that of amino-acid-fed cells. Insulin slowed inactivation in the absence of most amino acids in a protein-synthesis-independent manner, but insulin did not influence the more rapid inactivation observed in amino-acid-fed cells. These results indicate that the level of System A activity observed in response to regulation by amino acids represents a balance between carrier synthesis and inactivation, which can be positively or negatively influenced by growth factors.
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PMID:Hormonal regulation of the System A amino acid transport adaptive response mechanism in a kidney epithelial cell line (MDCK). 388 63

Plasma membrane vesicles prepared from intact rat liver or isolated hepatocytes retain transport activity by systems A, ASC, N, and Gly. Selective substrates for these systems showed a Na+-dependent overshoot indicative of energy-dependent transport, in this instance, driven by an artificially-imposed Na+ gradient. Greater than 85% of Na+-dependent 2-aminoisobutyric acid (AIB) uptake was blocked by an excess of 2-(methylamino)isobutyric acid (MeAIB) with an apparent Ki of 0.6 mM. Intact hepatocytes obtained from glucagon-treated rats exhibited a stimulation of system A activity and plasma membrane vesicles isolated from those same cells partially retained the elevated activity. Transport activity induced by substrate starvation of cultured hepatocytes was also evident in membrane vesicles prepared from those cells. The membrane-bound glucagon-stimulated system A activity decays rapidly during incubation of vesicles at 4 degrees C (t1/2 = 13 h), but not at -75 degrees C. Several different inhibitors of proteolysis were ineffective in blocking the decay of transport activity. Hepatic system N transport activity was also elevated in plasma membrane vesicles from glucagon-treated rats, whereas system ASC was essentially unchanged. The results indicate that both glucagon and adaptive regulation cause an induction of amino acid transport through a plasma membrane-associated protein.
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PMID:Maintenance of glucagon-stimulated system A amino acid transport activity in rat liver plasma membrane vesicles. 396 88

The transport of L-glutamic acid has been studied in skin-derived diploid human fibroblasts. Competition analysis in the presence and absence of Na+ and mathematical discrimination by nonlinear regression indicated that L-glutamic acid enters the cell by at least three transport systems: 1) a high affinity Na+-dependent system which has been found to be identical to the previously described system for anionic amino acids (Gazzola, G. C., Dall'Asta, V., Bussolati, O., Makowske, M., and Christensen, H. N. (1981) J. Biol. Chem. 256, 6054-6059) and which is provisionally designated as System X-AG; this route was shared by L-aspartic acid; 2) a low affinity Na+-dependent system resembling the ASC System for neutral amino acids (Franchi-Gazzola, R., Gazzola, G. C., Dall'Asta, V., and Guidotti, G. G. (1982) J. Biol. Chem. 257, 9582-9587); its reactivity toward L-glutamic acid was strongly inhibited by L-serine, but not by 2-(methyl-amino)isobutyric acid; and 3) a Na+-independent system similar to System XC- described in fetal human lung fibroblasts (Bannai, S., and Kitamura, E. (1980) J. Biol. Chem. 255, 2372-2376). The XC- system served for L-glutamic acid and L-cystine, the latter amino acid behaving as a potent inhibitor of L-glutamic acid uptake. Amino acid starvation did not change the uptake of L-glutamic acid by the two Na+-dependent systems, but enhanced the activity of System XC- by increasing its Vmax. L-Glutamic acid transport was also affected by the density of the culture. An increased cell density lowered the uptake of the amino acid by Systems ASC and XC- and promoted the uptake by System X-AG. All these variations were dependent upon changes in Vmax.
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PMID:Pathways of L-glutamic acid transport in cultured human fibroblasts. 613 63


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