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

Catecholamines induced an increase in the activity of rat adipose tissue and liver phosphopyruvate carboxylases that was maintained for 48h. The response of adipose tissue phosphopyruvate carboxylase was blocked by actinomycin D, corticosteroids and propranolol, whereas corticosteroids and propranolol did not affect the liver enzyme. Cortisol phosphate, like actinomycin D, interfered only with the initiation of the increase in enzyme activity caused by noradrenaline, but not with the process of enzyme accumulation. In contrast, cycloheximide was effective in blocking enzyme induction throughout the course of the catecholamine effect. Adrenocorticotrophic hormone caused a short-term induction of adipose tissue phosphopyruvate carboxylase, which could be blocked by propranolol. Hepatic phosphopyruvate carboxylase, but not the adipose tissue enzyme, was induced by dibutyryladenosine 3':5'-cyclic monophosphate and by glucagon. Both nicotinic acid and nicotinamide decreased the normal induction of adipose tissue phosphopyruvate carboxylase caused by starvation, but only nicotinamide increased the activity of the liver enzyme.
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PMID:The interaction of catecholamines and adrenal corticosteroids in the induction of phosphopyruvate carboxylase in rat liver and adipose tissue. 434 97

1. The purpose of this study was to determine the nature of the metabolic changes associated with carbohydrate and fat metabolism that occurred in the blood and liver of lactating dairy cows during starvation for 6 days. 2. During starvation, the blood concentrations of the free fatty acids and ketone bodies increased, whereas that of citrate decreased. After an initial increase, the blood concentration of glucose subsequently declined as starvation progressed. Starvation caused a significant decrease in the plasma concentration of serine and a significant increase in that of leucine. 3. After 6 days of starvation the hepatic concentrations of oxaloacetate, citrate, phosphoenolpyruvate, 2-phosphoglycerate, 3-phosphoglycerate, glucose, glycogen, ATP and NAD(+) had all decreased, as had the hepatic activities of phosphopyruvate carboxylase (EC 4.1.1.32) and pyruvate kinase (EC 2.7.1.40). 4. The above metabolic changes are similar to those previously found to occur in cows suffering from spontaneous ketosis (Baird et al., 1968; Baird & Heitzman, 1971). 5. Milk yield decreased progressively during starvation. 6. There were marked differences in the ability of individual animals to resist the onset of severe starvation ketosis.
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PMID:Effects of starvation on intermediary metabolism in the lactating cow. A comparison with metabolic changes occurring during bovine ketosis. 434 57

Unusual guanosine nucleotides guanosine 5'-diphosphate 3'-diphosphate (ppGpp, also known as MSI) and guanosine 5'-diphosphate 3'-monophosphate (ppGp, also known as MSIII) accumulate to high concentrations in wild-type cells of Escherichia coli during amino acid starvation. We reported here that both nucleotides strongly inhibit the activity of enzymes IMP dehydrogenase and adenylosuccinate synthetase, the first enzymes of the guanylate and adenylate biosynthetic pathways. In both cases, ppGP (MSII) is a stronger inhibitor than ppGpp (MSI). On the other hand, these two nucleotides exhibited opposite effects on the activity of phosphoenolpyruvate carboxylase, the enzyme that utilizes phosphoenolpyruvate. At their respective physiological concentrations, the activity of phosphoenolpyruvate carboxylase is activated by ppGpp and inhibited by ppGp.
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PMID:Effect of unusual guanosine nucleotides on the activities of some Escherichia coli cellular enzymes. 611 28

To analyze the role of phosphoenolpyruvate carboxylase (PEPCase, EC 4.1.1.31) during seed development, two cDNA clones encoding two isoforms of PEPCase were isolated from a seed-specific library of Vicia faba. The two sequences (VfPEPCase1 and VfPEPCase2) have a sequence identity of 82 and 89% on the nucleotide and amino acid levels. The VfPEPCase1 mRNA was found to be predominantly expressed in roots and developing cotyledons whereas the VfPEPCase2 mRNA was more abundant in green and maternal tissues. In the cotyledons, PEPCase mRNAs accumulated from early to mid cotyledon stage and decreased thereafter. The PEPCase activity increased continuously during cotyledon development. The enzyme was strongly activated by glucose-6-phosphate, but not by glucose, fructose or sucrose. Asparagine was weakly activating whereas malate, aspartate and glutamate were inhibitory. The inhibitors became less effective with increasing pH. Aspartate was a much stronger inhibitor of cotyledonary PEPCase than glutamate at both pH 7.0 and 7.5. The sensitivity of PEPCase to malate inhibition decreased from early to mid cotyledon stage at a time when storage proteins are synthesized. This indicates activation on the protein level, possibly by protein phosphorylation. Nitrogen starvation in the presence of hexoses but not sucrose decreased mRNA levels of VfPEPCase1 and enzyme activity, indicating control on the mRNA level by both carbon and nitrogen. It is concluded that in developing cotyledons PEPCase is probably important for the synthesis of organic acids to provide carbon skeletons for amino acid synthesis.
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PMID:Phosphoenolpyruvate carboxylase in developing seeds of Vicia faba L.: gene expression and metabolic regulation. 1021 2

The metabolic responses occurring in cucumber (Cucumis sativus L.) roots (a strategy-I plant) grown under iron-deficiency conditions were studied in-vivo using 31P-nuclear magnetic resonance spectroscopy. Iron starvation induced activation of metabolism leading to the consumption of stored carbohydrates to produce the NAD(P)H, ATP and phosphoenolpyruvate necessary to sustain the increased activity of the NAD(P)H:Fe(3+)-reductase, the H(+)-ATPase (EC 3.6.1.35) and phosphoenolpyruvate carboxylase (EC 4.1.1.31). Activation of catabolic pathways was supported by the enhancement of glycolytic enzymes and concentrations of the metabolites glucose-6-phosphate and fructose-6-phosphate, and by enhancement of the respiration rate. Moreover, Fe-deficiency induced a slight increase in the cytoplasmic (pHc) and vacuolar (pHv) pHs as well as a dramatic decrease in the vacuolar phosphate (Pi) concentration. A comparison was done using fusicoccin (FC), a fungal toxin which stimulates proton extrusion. Changes in pHc and pHv were measured after addition of FC. Under these conditions, a dramatic alkalinization of the pHv of -Fe roots was observed, as well as a concomitant Pi movement from the vacuole to the cytoplasm. These results showed that Fe starvation was indeed accompanied by the activation of metabolic processes useful for sustaining the typical responses occurring at the plasma-membrane level (i.e. increases in the NAD(P)H:Fe(3+)-reductase and H(+)-ATPase activities) as well as those involved in the homeostasis of pHc. The decrease in vacuolar Pi levels induced by Fe-deficiency and FC and movement of Pi from the vacuole to the cytoplasm suggest a possible involvement of this compound in the cellular pH-stat system.
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PMID:Metabolic responses in cucumber (Cucumis sativus L.) roots under Fe-deficiency: a 31P-nuclear magnetic resonance in-vivo study. 1087 32

Phosphoenolpyruvate carboxylase (PEPC) specific activity increased by 250% following 8 to 10 days of Pi starvation of Brassica napus suspension cells. Densitometric scanning of PEPC immunoblots revealed a close correlation between PEPC activity and the amount of the antigenic 104-kDa PEPC subunit. To further assess the influence of Pi deprivation on PEPC, the enzyme was purified from Pi-sufficient (+Pi) and Pi-starved (-Pi) cells to electrophoretic homogeneity and final specific activities of 37-40 micromol phosphoenolpyruvate utilized per min per mg protein. Gel filtration, SDS/PAGE, and CNBr peptide mapping indicated that the +Pi and -Pi PEPCs are both homotetramers composed of an identical 104-kDa subunit. Respective pH-activity profiles, phosphoenolpyruvate saturation kinetics, and sensitivity to L-malate inhibition were also indistinguishable. Kinetic studies and phosphatase treatments revealed that PEPC of the +Pi and -Pi cells exists mainly in its dephosphorylated (L-malate sensitive) form. Thus, up-regulation of PEPC activity in -Pi cells appears to be solely due to the accumulation of the same PEPC isoform being expressed in +Pi cells. PEPC activity was modulated by several metabolites involved in carbon and nitrogen metabolism. At pH 7.3, marked activation by glucose 6-phosphate and inhibition by L-malate, L-aspartate, L-glutamate, DL-isocitrate, rutin and quercetin was observed. The following paper provides a model for the coordinate regulation of B. napus PEPC and cytosolic pyruvate kinase by allosteric effectors. L-Aspartate and L-glutamate appear to play a crucial role in the control of the phosphoenolpyruvate branchpoint in B. napus, particularly with respect to the integration of carbohydrate partitioning with the generation of carbon skeletons required during nitrogen assimilation.
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PMID:Purification and characterization of phosphoenolpyruvate carboxylase from Brassica napus (rapeseed) suspension cell cultures: implications for phosphoenolpyruvate carboxylase regulation during phosphate starvation, and the integration of glycolysis with nitrogen assimilation. 1088 Sep 70

The aim of this study was to investigate whether gluconeogenesis catalysed by phosphoenolpyruvate carboxykinase (PEPCK) occurs during leaf senescence. This was addressed by determining changes in the abundance and intercellular location of enzymes necessary for gluconeogenesis during the senescence of barley leaves and cucumber cotyledons. PEPCK was never present in barley leaves, despite the presence of large amounts of isocitrate lyase (ICL), a key enzyme of the glyoxylate cycle, and of its product, glyoxylate. Although PEPCK was present in non-senescent cucumber cotyledons, its abundance declined during senescence. Throughout senescence, PEPCK was only present in the trichomes and vasculature, whereas ICL was located in mesophyll cells. Pyruvate,Pi dikinase (PPDK) which, in concert with NAD(P)-malic enzyme, is also capable of catalysing gluconeogenesis, was present in non-senescent barley leaves and cucumber cotyledons, but in both plants its abundance decreased greatly during senescence. The abundance of ICL was greatly reduced in senescing detached barley leaves by either illumination or by co-incubation with sucrose, and greatly increased in darkened attached barley leaves. These results argue against the large-scale occurrence of gluconeogenesis during senescence catalysed either by PEPCK or PPDK. In cucumber cotyledons, PEPCK may play a role in metabolic processes linked to the export of amino acids, a role in which phosphoenolpyruvate carboxylase may also be involved. The amount of ICL was increased by starvation and during senescence may function in the conversion of lipids to organic acids, which are then utilised in the mobilisation of amino acids from leaf protein.
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PMID:Are isocitrate lyase and phosphoenolpyruvate carboxykinase involved in gluconeogenesis during senescence of barley leaves and cucumber cotyledons? 1103 56

Phosphoenolpyruvate carboxylase (PEPCase) activity was investigated in cucumber roots grown under iron starvation. The enzyme extracted from plants grown in the presence and in the absence of Fe was characterized both kinetically and biochemically. Extractable PEPCase activity was increased by 4-fold in the absence of Fe. This increase began about 5 d after Fe starvation. Western blot analysis revealed the presence of two polypeptides with apparent molecular masses of 103 and 108 kDa. At the beginning both the polypeptides were equally present in the control and in the Fe-deficient roots. After 10 d of Fe starvation the increase was clearly evident and concerned, in particular, the polypeptide of 103 kDa whose enhancement was around 3-fold with respect to the control. Re-supply of iron to Fe-starved roots decreased both the activity and the concentration of the enzyme to the control values. Determination of kinetic parameters revealed that the K:(m) values for the substrates were the same, while the V:(max) was increased by four times for the enzyme extracted from Fe-deficient roots. Also the responses to pH changes and to the allosteric modulators malate and glucose-6-phosphate were different. The kinetic data, the increase in PEPCase specific activity and in the PEPCase polypeptides concentration seem to indicate that under Fe deficiency the enzyme regulation might be, in part, exerted at the transcriptional level.
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PMID:Phosphoenolpyruvate carboxylase in cucumber (Cucumis sativus L.) roots under iron deficiency: activity and kinetic characterization. 1111 68

Excised maize (Zea mays L.) root tips were used to study the early metabolic effects of glucose (Glc) starvation. Root tips were prelabeled with [1-13C]Glc so that carbohydrates and metabolic intermediates were close to steady-state labeling, but lipids and proteins were scarcely labeled. They were then incubated in a sugar-deprived medium for carbon starvation. Changes in the level of soluble sugars, the respiratory quotient, and the 13C enrichment of intermediates, as measured by 13C and 1H nuclear magnetic resonance, were studied to detect changes in carbon fluxes through glycolysis and the tricarboxylic acid cycle. Labeling of glutamate carbons revealed two major changes in carbon input into the tricarboxylic acid cycle: (a) the phosphoenolpyruvate carboxylase flux stopped early after the start of Glc starvation, and (b) the contribution of glycolysis as the source of acetyl-coenzyme A for respiration decreased progressively, indicating an increasing contribution of the catabolism of protein amino acids, fatty acids, or both. The enrichment of glutamate carbons gave no evidence for proteolysis in the early steps of starvation, indicating that the catabolism of proteins was delayed compared with that of fatty acids. Labeling of carbohydrates showed that sucrose turnover continues during sugar starvation, but gave no indication for any significant flux through gluconeogenesis.
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PMID:Sugar-Starvation-Induced Changes of Carbon Metabolism in Excised Maize Root Tips. 1222 77

To study the regulation of gene expression for enzymes in the C4 photosynthetic pathway of maize (Zea mays L.) in response to changing N status in developing photosynthetic cells, we have studied in vitro transcription of the phosphoenolpyruvate carboxylase (PEPC) gene in leaf nuclei isolated from plants during recovery from N starvation. The induction was specific for the C4-type PEPC gene (C4Ppc1), and its transcription was N dependent and increased markedly by supply of an N source, but there was a discrepancy between the steady-state levels of mRNA and the stimulation of in vitro transcription. The results suggest that the N-inducible expression of C4Ppc1 is regulated both transcriptionally and posttranscriptionally by N availability. The in vitro transcription rate of C4Ppc1 was greatly stimulated by incubating detached leaves with zeatin alone, whereas the rate remained essentially unchanged by incubating with an exogenous N source alone. The results, taken together, imply that cytokinins up-regulate the transcription of C4Ppc1 in response to N status, whereas glutamine and/or its metabolite(s) up-regulate the level of the transcript. The transcription was totally inhibited by cycloheximide, indicating that the cytokinin-dependent transcription of C4Ppc1 requires the synthesis of protein.
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PMID:Transcriptional and Posttranscriptional Regulation of Nitrogen-Responding Expression of Phosphoenolpyruvate Carboxylase Gene in Maize. 1223 78


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