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Query: UMLS:C0038187 (starvation)
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In lepidopteran larvae, three transport mechanisms are involved in the active and electrogenic K(+) secretion that occurs in the epithelial goblet cells of the midgut. These consist of (i) basolateral K(+) channels, allowing K(+) entry from the haemolymph into the cytosol, (ii) apical electrogenic K(+)/2H(+) antiporters, which are responsible for secondary active extrusion of K(+) from the cell into the gut lumen via the goblet cavity and (iii) apical V-ATPase-type proton pumps. The latter energize apical K(+) exit by building up a large, cavity-positive electrical potential that drives the antiporters. Net K(+) secretion (I(K)) can be measured as short-circuit current (I(sc)) across the in vitro midgut mounted in an Ussing chamber. We investigated the influence of protons on the transepithelial I(K) and the partial reactions of the basolateral K(+) permeability (P(K)) and the apical, lumped 'K(+) pump' current (I(P)) at various extra- and intracellular pH values. In particular, we wanted to know whether increased cellular acidity could counteract the reversible dissociation of the V-ATPase into its V(1) and V(o) parts, as occurs in yeast after glucose deprivation and in the midgut of Manduca sexta during starvation or moulting, thus possibly enhancing K(+) transport. When intact epithelia were perfused with high-[K(+)] (32 mmol l(-1)) salines with different pH values, I(K) was reversibly reduced when pH values fell below 6 on either side of the epithelium. Attempts to modify the intracellular pH by pulsing with NH(4)(+) or propionate showed that intracellular acidification caused a reduction in I(K) similar to that obtained in response to application of external protons. Treatment with azide, a well-known inhibitor of the mitochondrial ATP synthase, had the same effect as pulsing with ammonium or propionate with, however, much faster kinetics and higher reversibility. Breakdown of the basolateral or apical barrier using the antibiotic nystatin allowed the intracellular pH to be clamped to that of the saline facing the nystatin-treated epithelial border. Cell acidification achieved by this manipulation led to a reduction in both apical I(P) and basolateral P(K). The transepithelial I(K) showed an approximately half-maximal reduction at external pH values close to 5 in intact tissues, and a similar reduction in I(P) and P(K) values was seen at an intracellular pH of 5 in nystatin-permeabilised epithelia. Thus, the hypothesized V(1)V(o) stabilization by cell acidity is not reflected in the pH-sensitivity of I(P). Moreover, all components that transport K(+) are synchronously inhibited below pH 6. The significance of our findings for the midgut in vivo is discussed.
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PMID:Insect midgut K(+) secretion: concerted run-down of apical/basolateral transporters with extra-/intracellular acidity. 1189 60

V-ATPases are complex proteins consisting of a peripheral, ATP-hydrolysing V(1) complex and a membrane-bound H(+)-translocating V(o) complex. The plasma membrane V-ATPase from the tobacco hornworm (Manduca sexta) midgut is made up of eight different V(1) and four different V(o) subunits. During starvation and moulting, V-ATPase activity decreases as a result of the dissociation of the V(1) complex from the V(o) complex. To determine whether subunit biosynthesis is reduced during periods of enzyme inactivity, we measured the transcript levels and transcriptional activities of V-ATPase genes. Northern blots revealed the downregulation of almost all V-ATPase transcripts during starvation. During moulting, transcript levels of the three V-ATPase genes examined, mvB, mvG and mvd, also decreased, and this decrease was negatively correlated with the titre of 20-hydroxyecdysone (20-HE) and positively correlated with the titre of juvenile hormone (JH). To test the biological significance of these correlations, we injected both hormones into feeding larvae and measured transcript levels several hours later. A short-term increase and a long-term decrease in levels of mRNA were observed after 20-HE injection, whereas JH injection had no significant effect. Immunohistochemical studies of the midgut epithelium revealed that 20-HE injection led to changes in goblet cell morphology and in the subcellular distribution of the V(1) complex comparable with the situation during the moult and during starvation. Reporter gene assays in Sf21 cells using mvB, mvG and mvd promoters to initiate transcription of firefly luciferase led, after incubation of the cells with 20-HE, to results comparable with those obtained in the injection experiments. These findings suggest that putative ecdysone-responsive elements are present in all three promoters. Taken together, our results suggest that the expression of V-ATPase genes is controlled in a coordinated manner by ecdysteroids.
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PMID:Expression of Manduca sexta V-ATPase genes mvB, mvG and mvd is regulated by ecdysteroids. 1191 65

In roots of tomato ( Lycopersicon esculentum Mill.), extranumerary root hairs and transfer cell-like wall ingrowth depositions in the rhizodermis were developed in response to P and Fe deficiency. Immunocytolocalization of the plasma membrane H(+)-ATPase in roots of P-deficient plants revealed no appreciable increase in H(+)-ATPase density relative to control plants. In transfer cells, immunogold labeling was considerably higher than in ordinary rhizodermal cells. H(+)-ATPase sites were asymmetrically distributed in cells with and without wall ingrowths under P-deficient conditions. A split-root study revealed that the frequency of transfer cells was higher in the low-P half of the root system, but the density of H(+)-ATPase molecules was enhanced only in the high-P half of the split roots, suggesting that formation of transfer cells was controlled directly by the external Pi concentration, whereas ATPase expression was regulated indirectly by the internal nutrient status of the plant. The role of hormones in the induction of transfer cells was investigated by treating plants with the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) or various ethylene antagonists. Transfer cells were induced by ACC to an extent similar to that observed after P or Fe starvation, but inhibitors of either ethylene synthesis or action did not decrease their frequency. These results suggest that ethylene was not required for the induction of transfer cells but changes in ethylene levels appeared to modulate the number of cells forming wall ingrowths. In roots of ethylene-insensitive Never-ripe tomato plants the frequency of transfer cells was rather increased than decreased under most growth conditions relative to the wild type, indicating that ethylene responsiveness played no critical role in the differentiation of transfer cells and that the transduction of signals ultimately leading to their formation was independent of the ethylene signaling cascade.
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PMID:Formation of transfer cells and H(+)-ATPase expression in tomato roots under P and Fe deficiency. 1202 80

The kdpFABC operon, coding for a high-affinity K(+)-translocating P-type ATPase, is expressed in Escherichia coli as a backup system during K(+) starvation or an increase in medium osmolality. Expression of the operon is regulated by the membrane-bound sensor kinase KdpD and the cytosolic response regulator KdpE. From a nitrogen-fixing cyanobacterium, Anabaena sp. strain L-31, a kdpDgene was cloned (GenBank accession no. AF213466) which codes for a KdpD protein (365 amino acids) that lacks both the transmembrane segments and C-terminal transmitter domain and thus is shorter than E. coli KdpD. A chimeric kdpD gene was constructed and expressed in E. coli coding for a protein (Anacoli KdpD), in which the first 365 amino acids of E. coli KdpD were replaced by those from Anabaena KdpD. In everted membrane vesicles, this chimeric Anacoli KdpD protein exhibited activities, such as autophosphorylation, transphosphorylation and ATP-dependent dephosphorylation of E. coli KdpE, which closely resemble those of the E. coli wild-type KdpD. Cells of E. coli synthesizing Anacoli KdpD expressed kdpFABC in response to K(+) limitation and osmotic upshock. The data demonstrate that Anabaena KdpD can interact with the E. coliKdpD C-terminal domain resulting in a protein that is functional in vitro as well as in vivo.
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PMID:A chimeric Anabaena/ Escherichia coli KdpD protein (Anacoli KdpD) functionally interacts with E. coli KdpE and activates kdp expression in E. coli. 1211 59

F forms stable complexes with Al at conditions found in the soil. Fluoroaluminate complexes (AlF(x)) have been widely described as effective analogs of inorganic phosphate (Pi) in Pi-binding sites of several proteins. In this work, we explored the possibility that the phytotoxicity of AlF(x) reflects their activity as Pi analogs. For this purpose, (32)P-labeled phosphate uptake by excised roots and plasma membrane H(+)-ATPase activity were investigated in an Al-tolerant variety of maize (Zea mays L. var. dwarf hybrid), either treated or not with AlF(x). In vitro, AlF(x) competitively inhibited the rate of root phosphate uptake as well as the H(+)-ATPase activity. Conversely, pretreatment of seedlings with AlF(x) in vivo promoted no effect on the H(+)-ATPase activity, whereas a biphasic effect on Pi uptake by roots was observed. Although the initial rate of phosphate uptake by roots was inhibited by AlF(x) pretreatment, this situation changed over the following minutes as the rate of uptake increased and a pronounced stimulation in subsequent (32)Pi uptake was observed. This kinetic behavior suggests a reversible and competitive inhibition of the phosphate transporter by fluoroaluminates. The stimulation of root (32)Pi uptake induced by AlF(x) pretreatment was tentatively interpreted as a phosphate starvation response. This report places AlF(3) and AlF(4)(-) among Al-phytotoxic species and suggests a mechanism of action where the accumulation of Pi-mimicking fluoroaluminates in the soil may affect the phosphate absorption by plants. The biochemical, physiological, and environmental significance of these findings is discussed.
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PMID:Inhibition of phosphate uptake in corn roots by aluminum-fluoride complexes. 1217 89

We have characterized sulfate transport in the unicellular green alga Chlamydomonas reinhardtii during growth under sulfur-sufficient and sulfur-deficient conditions. Both the Vmax and the substrate concentration at which sulfate transport is half of the maximum velocity of the sulfate transport (K1/2) for uptake were altered in starved cells: the Vmax increased approximately 10-fold, and the K1/2 decreased approximately 7-fold. This suggests that sulfur-deprived C. reinhardtii cells synthesize a new, high-affinity sulfate transport system. This system accumulated rapidly; it was detected in cells within 1 h of sulfur deprivation and reached a maximum by 6 h. A second response to sulfur-limited growth, the production of arylsulfatase, was apparent only after 3 h of growth in sulfur-free medium. The enhancement of sulfate transport upon sulfur starvation was prevented by cycloheximide, but not by chloramphenicol, demonstrating that protein synthesis on 80S ribosomes was required for the development of the new, high-affinity system. The transport of sulfate into the cells occurred in both the light and the dark. Inhibition of ATP formation by the antibiotics carbonylcyanide m-chlorophenylhydrazone and gramicidin-S and inhibition of either F- or P-type ATPases by N,N-dicyclohexylcarbodiimide and vanadate completely abolished sulfate uptake. Furthermore, nigericin, a carboxylate ionophore that exchanges H+ for K+, inhibited transport in both the light and the dark. Finally, uptake in the dark was strongly inhibited by valinomycin. These results suggest that sulfate transport in C. reinhardtii is an energy-dependent process and that it may be driven by a proton gradient generated by a plasma membrane ATPase.
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PMID:Characterization of Sulfate Transport in Chlamydomonas reinhardtii during Sulfur-Limited and Sulfur-Sufficient Growth. 1223 42

The major life-threatening event for lactic acid bacteria (LAB) in their natural environment is the depletion of their energy sources and LAB can survive such conditions only for a short period of time. During periods of starvation LAB can exploit optimally the potential energy sources in their environment usually by applying proton motive force generating membrane transport systems. These systems include in addition to the proton translocating F0F1-ATPase: a respiratory chain when hemin is present in the medium, electrogenic solute uptake and excretion systems, electrogenic lactate/proton symport and precursor/product exchange systems. Most of these metabolic energy-generating systems offer as additional bonus the prevention of a lethal decrease of the internal and external pH. LAB have limited biosynthetic capacities and rely heavily on the presence of essential components such as sources of amino acids in their environment. The uptake of amino acids requires a major fraction of the available metabolic energy of LAB. The metabolic energy cost of amino acid uptake can be reduced drastically by accumulating oligopeptides instead of the individual amino acids and by proton motive force-generating efflux of excessively accumulated amino acids. Other life-threatening conditions that LAB encounter in their environment are rapid changes in the osmolality and the exposure to cytotoxic compounds, including antibiotics. LAB respond to osmotic upshock or downshock by accumulating or releasing rapidly osmolytes such as glycine-betaine. The life-threatening presence of cytotoxic compounds, including antibiotics, is effectively counteracted by powerful drug extruding multidrug resistance systems. The number and variety of defense mechanisms in LAB is surprisingly high. Most defense mechanisms operate in the cytoplasmic membrane to control the internal environment and the energetic status of LAB. Annotation of the functions of the genes in the genomes of LAB will undoubtedly reveal additional defense mechanisms.
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PMID:The cell membrane and the struggle for life of lactic acid bacteria. 1236 97

The short-time transcriptional response of yeast cells to a mild increase in external pH (7.6) has been investigated using DNA microarrays. A total of 150 genes increased their mRNA level at least twofold within 45 min. Alkalinization resulted in the repression of 232 genes. The response of four upregulated genes, ENA1 (encoding a Na+-ATPase also induced by saline stress) and PHO84, PHO89 and PHO12 (encoding genes upregulated by phosphate starvation), was characterized further. The alkaline response of ENA1 was not affected by mutation of relevant genes involved in osmotic or oxidative signalling, but was decreased in calcineurin and rim101 mutants. Mapping of the ENA1 promoter revealed two pH-responsive regions. The response of the upstream region was fully abolished by the drug FK506 or mutation of CRZ1 (a transcription factor activated by calcium/calcineurin), whereas the response of the downstream region was essentially calcium independent. PHO84 and PHO12 responses were unaffected in crz1 cells, but required the presence of Pho2 and Pho4. In contrast, part of the alkali-induced expression of PHO89 was maintained in pho4 or pho2 cells, but was fully abolished in a crz1 strain or in the presence of FK506. Heterologous promoters carrying the minimal calcineurin-dependent response elements found in ENA1 or FKS2 were able to drive alkaline pH-induced expression. These results demonstrate that the transcriptional response to alkaline pH involves different signalling mechanisms, and that calcium signalling is a relevant component of this response.
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PMID:The transcriptional response to alkaline pH in Saccharomyces cerevisiae: evidence for calcium-mediated signalling. 1245 18

PMA1 and PMA2 genes encode Saccharomyces cerevisiae plasma membrane H(+)-ATPase (PM-H(+)-ATPase), an enzyme with critical physiological roles both in the absence or presence of environmental stress. The two PM-H(+)-ATPase isoforms differ in their biochemical characteristics but, under all the growth conditions that were examined so far, PMA2 expression is negligible and Pma1p accounts for practically the totality of cell PM-H(+)-ATPase activity. In the present work, we have compared gene expression levels and activity of this proton pump in yeast cells cultivated under fermentative or respiratory growth and under carbon starvation. The expression levels of both PMA1 and PMA2 genes were consistently higher (2.5-4.5-fold) in cells cultivated under respiratory metabolism (in ethanol-based medium or after the diauxic shift), than in cells cultivated under fermentative metabolism (during the full period of growth in a medium where glucose is not the limiting nutrient or during the first period of diauxic growth in low-glucose-based medium). The moderate upregulation of PMA1 and PMA2 transcription in cells grown on ethanol compared with those grown on glucose was reflected in the increased content and activity of PM-H(+)-ATPase. In diauxic growth, during transition to stationary phase after ethanol depletion, a further strong activation (eight-fold) of PMA2 gene transcription was observed. Although PMA2 transcription still remains quite below (20-fold) PMA1 transcription, this is the first environmental condition, identified so far, that leads to a significant PMA2 expression, suggesting that this PM-H(+)-ATPase isoform may play some role during carbon starvation.
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PMID:Transcription patterns of PMA1 and PMA2 genes and activity of plasma membrane H+-ATPase in Saccharomyces cerevisiae during diauxic growth and stationary phase. 1255 74

Combined transcriptome and proteome analysis was carried out to understand metabolic and physiological changes of Escherichia coli during the high cell density cultivation (HCDC). The expression of genes of TCA cycle enzymes, NADH dehydrogenase and ATPase, was up-regulated during the exponential fed-batch period and was down-regulated afterward. However, expression of most of the genes involved in glycolysis and pentose phosphate pathway was up-regulated at the stationary phase. The expression of most of amino acid biosynthesis genes was down-regulated as cell density increased, which seems to be the major reason for the reduced specific productivity of recombinant proteins during HCDC. The expression of chaperone genes increased with cell density, suggesting that the high cell density condition itself can be stressful to the cells. Severe competition for oxygen at high cell density seemed to make cells use cytochrome bd, which is less efficient but has a high oxygen affinity than cytochrome bo(3). Population cell density itself strongly affected the expression of porin protein genes, especially ompF, and hence the permeability of the outer membrane. Expression of phosphate starvation genes was most strongly up-regulated toward the end of cultivation. It was also found that sigma(E) (rpoE) plays a more important role than sigma(S) (rpoS) at the stationary phase of HCDC. These findings should be invaluable in designing metabolic engineering and fermentation strategies for the production of recombinant proteins and metabolites by HCDC of E. coli.
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PMID:Combined transcriptome and proteome analysis of Escherichia coli during high cell density culture. 1255 8


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