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

Cellular content and rates of synthesis of the apoprotein subunits of phycocyanin in Anacystis nidulans cultures undergoing, and recovering from, nitrate starvation were measured by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of total and immunoprecipitable soluble proteins. Results indicated that (i) nitrate starvation provokes coordinate degradation of apoprotein subunits: (ii) de novo synthesis of these subunits is selectively depressed during starvation; (iii) nitrate restoration provokes coordinate increases in the rates of synthesis of these subunits, although maximal rates are not achieved for 6 to 10 h after readdition of nitrate; and (iv) illumination affects both relative and absolute rates of apoprotein formation.
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PMID:Phycocyanin synthesis and degradation in the blue-green bacterium Anacystis nidulans. 92 72

A simple and rapid procedure to make yeast cells permeable by agitating with toluene-ethanol, (TE) 1:4, v/v was developed. The permeated cells retained their ability to catalyze certain enzyme reactions. Temperature and duration of agitation during TE treatment played an important role in retention of the catalytic potential of permeated cells. The in situ assay using permeated cell preparations was more sensitive even in the absence of added cofactors than in the vitro assay in detecting assimilatory nitrate reductase (NAD(P)H:nitrate oxidoreductase, EC 1.6.6.2) (NAR) activity in Candida utilis. Using in situ assay technique, different mechanisms regulating the biosynthesis of NAR in C. utilis were investigated. Nitrogen starvation did not lead to derepression of NAR. NO3-ions were absolutely essential for induction and maintenance of high levels of NAR activity. Cells grown on ammonium nitrate possessed relatively lower levels of NAR. Kinetics of NAR induction were followed as a function of time and inducer concentration. The influence of various cations on the induction of NAR by nitrate was investigated. A wide range of D-amino acids induced NAR synthesis. Of 22 L-amino acids tested only phenylalanine induced significant levels of NAR. Various intermediates of the pathway of nitrate reduction influenced the rate of NAR induction. There was a rapid disappearance of in vivo activity of the enzyme of induced yeast cells on nitrogen starvation, and the rate of loss was accelerated by the presence of NH4+.
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PMID:Regulatory properties of yeast nitrate reductase in situ. 94 16

Cylindrotheca fusiformis is shown to be able to convert glycolate to glycerate via tartronic semialdehyde as well as by the better known route involving transamination to glycine. Enzymes related to photorespiration were compared in light-dark synchronized cultures of C. fusiformis kept in continuous light in a complete synthetic seawater medium or starved for nitrogen or silicon. Glycolate oxidation remained constant throughout the cell cycle and was unaffected by starvation. Transamination of glyoxylate was stimulated by light, inhibited during nitrogen starvation, and dramatically stimulated by reintroduction of nitrate to the medium. Glyoxylate carboligase was also stimulated by light and inhibited during nitrogen-starvation but only partially recovered activity after reintroduction of nitrate.
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PMID:Photorespiration in diatoms. IV. Two pathways of glycolate metabolism in synchronized cultures of Cylindrotheca fusiformis. 101 49

Chloramphenicol completely inhibited the activity of existing denitrification enzymes in acetylene-block incubations with (i) sediments from a nitrate-contaminated aquifer and (ii) a continuous culture of denitrifying groundwater bacteria. Control flasks with no antibiotic produced significant amounts of nitrous oxide in the same time period. Amendment with chloramphenicol after nitrous oxide production had begun resulted in a significant decrease in the rate of nitrous oxide production. Chloramphenicol also decreased (greater than 50%) the activity of existing denitrification enzymes in pure cultures of Pseudomonas denitrificans that were harvested during log-phase growth and maintained for 2 weeks in a starvation medium lacking electron donor. Short-term time courses of nitrate consumption and nitrous oxide production in the presence of acetylene with P. denitrificans undergoing carbon starvation were performed under optimal conditions designed to mimic denitrification enzyme activity assays used with soils. Time courses were linear for both chloramphenicol and control flasks, and rate estimates for the two treatments were significantly different at the 95% confidence level. Complete or partial inhibition of existing enzyme activity is not consistent with the current understanding of the mode of action of chloramphenicol or current practice, in which the compound is frequently employed to inhibit de novo protein synthesis during the course of microbial activity assays. The results of this study demonstrate that chloramphenicol amendment can inhibit the activity of existing denitrification enzymes and suggest that caution is needed in the design and interpretation of denitrification activity assays in which chloramphenicol is used to prevent new protein synthesis.
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PMID:Inhibition of existing denitrification enzyme activity by chloramphenicol. 162 47

Glutamine synthetase activity from Synechocystis sp. strain PCC 6803 is regulated as a function of the nitrogen source available in the medium. Addition of 0.25 mM NH4Cl to nitrate-grown cells promotes a clear short-term inactivation of glutamine synthetase, whose enzyme activity decreases to 5 to 10% of the initial value in 25 min. The intracellular levels of glutamine, determined under various conditions, taken together with the results obtained with azaserine (an inhibitor of transamidases), rule out the possibility that glutamine per se is responsible for glutamine synthetase inactivation. Nitrogen starvation attenuates the ammonium-mediated glutamine synthetase inactivation, indicating that glutamine synthetase regulation is modulated through the internal balance between carbon-nitrogen compounds and carbon compounds. The parallelism observed between the glutamine synthetase activity and the internal concentration of alpha-ketoglutarate suggests that this metabolite could play a role as a positive effector of glutamine synthetase activity in Synechocystis sp. Despite the similarities of this physiological system to that described for enterobacteria, the lack of in vivo 32P labeling of glutamine synthetase during the inactivation process excludes the existence of an adenylylation-deadenylylation system in this cyanobacterium.
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PMID:Regulation of glutamine synthetase activity in the unicellular cyanobacterium Synechocystis sp. strain PCC 6803 by the nitrogen source: effect of ammonium. 167 97

The effects of different culture conditions on nitrate reductase activity and nitrate reductase protein from Monoraphidium braunii have been studied, using two different immunological techniques, rocket immunoelectrophoresis and an enzyme-linked immunosorbent assay, to determine nitrate reductase protein. The nitrogen sources ammonium and glutamine repressed nitrate reductase synthesis, while nitrite, alanine, and glutamate acted as derepressors. There was a four- to eightfold increase of nitrate reductase activity and a twofold increase of nitrate reductase protein under conditions of nitrogen starvation versus growth on nitrate. Nitrate reductase synthesis was repressed in darkness. However, when Monoraphidium was grown under heterotrophic conditions with glucose as the carbon and energy source, the synthesis of nitrate reductase was maintained. With ammonium or darkness, changes in nitrate reductase activity correlated fairly well with changes in nitrate reductase protein, indicating that in both cases loss of activity was due to repression and not to inactivation of the enzyme. Experiments using methionine sulfoximine, to inhibit ammonium assimilation, showed that ammonium per se and not a product of its metabolism was the corepressor of the enzyme. The appearance of nitrate reductase activity after transferring the cells to induction media was prevented by cycloheximide and by 6-methylpurine, although in this latter case the effect was observed only in cells preincubated with the inhibitor for 1 h before the induction period.
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PMID:Immunological approach to the regulation of nitrate reductase in Monoraphidium braunii. 291 54

The addition of DL-7-azatryptophan (AZAT), a tryptophan analog, to continuous cultures of Anabaena sp. strain CA grown with 10 mM nitrate as the nitrogen source resulted in the differentiation of heterocysts. Analysis of the intracellular amino acid pools of Anabaena sp. strain CA after the addition of AZAT showed a marked decline in the intracellular glutamate pool and a slight increase in the levels of glutamine. The in vitro activity of glutamate synthase, the second enzyme involved in primary ammonia assimilation in Anabaena spp., was partially inhibited by the presence of AZAT at concentrations which are effective in triggering heterocyst formation (15% inhibition at 10 microM AZAT and up to 85% inhibition at 1.0 mM AZAT). Azaserine, a glutamine analog and potent glutamate synthase inhibitor, had no effect on the triggering of heterocyst development from undifferentiated batch and continuous cultures of Anabaena sp. strain CA. However, the presence of 1.0 microM azaserine significantly decreased the intracellular glutamate pool and increased the glutamine pool. The addition of AZAT also caused a decrease in the C-phycocyanin content of Anabaena sp. strain CA as a result of its proteolytic degradation. AZAT also had an inhibitory effect on the nitrogenase activity of Anabaena sp. strain CA. All these results suggest that AZAT causes a general nitrogen starvation of Anabaena sp. strain CA filaments, triggering heterocyst synthesis.
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PMID:Nitrogen starvation mediated by DL-7-azatryptophan in the cyanobacterium Anabaena sp. strain CA. 310 56

Replacement of the normal culture liquid to a nitrate-free medium resulted in an immediate drop in the ratio of protein to lipid in isolated cell envelopes of Anacystis nidulans cells. The relative fluidity of the envelope membranes or liposomes, made from the extracted lipids of the envelope, was estimated by measuring the steady-state fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene. A thermotrophic phase transition of lipids within the cytoplasmic membrane of intact cells was also revealed by detecting the temperature-dependent absorption changes in the proportion of zeaxanthin at 390 nm. It became evident that a decrease in the proportion of protein to lipid within the cell envelope was accompanied neither by changes in the microviscosity level, nor by shifting of characteristic temperatures of the liquid-crystalline-to-gel transition of lipids. In parallel with nitrate starvation, however, the proportion of saturated fatty acids of the envelope lipids increased markedly. Accumulation of saturated, longer-chain (C18) fatty acids at the cost of C16 counterparts upon nitrate deprivation occurred in all of the complex lipids. In accordance with these findings, a pronounced decrease in the fluidity was demonstrated for the liposomes prepared from the envelope polar lipids of nitrate-starved cells compared with the corresponding control, throughout the temperature range (45-5 degrees C) studied. We propose that the fluidizing effect due to a fall in the ratio of protein to lipid was compensated by a rapidly triggering regulatory process which enables the preservation of the fluidity characteristics at an optimal level within the cell envelope of A. nidulans.
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PMID:Nitrate starvation induces homeoviscous regulation of lipids in the cell envelope of the blue-green alga, Anacystis nidulans. 310 3

The main regulatory mechanisms controlling the synthesis of neural protease in batch cultures of a strain of Aspergillus were studied. Protease was inducible in this strain. No activity appeared during the trophophase when the organism was grown in a minimal medium, unless an inducer was added. Gelatine had the best induction effect among all the tested substances. The growth kinetics and enzyme production in a culture medium containing gelatine as the sole carbon and nitrogen source was determined. In spite of these results, protease activity was clearly detectable during the idiophase in absence of an external inducer. Furthermore, the addition of gelatine to cultures during the idiophase resulted in a decrease of the enzyme activity. This behaviour could be due to internal autoinduction generated by accelerated protein turnover of the nitrogen starved cells. The addition of gelatine probably reduced the protein starvation. Protease synthesis was sensitive to repression by rapidly assimilable carbon sources such as glucose and glycerol. Ammonia also caused an important repression, while nitrate and amino nitrogen had no effect. It was concluded that the synthesis of this enzyme is controlled by induction, catabolite repression, and ammonia repression, and that the enzyme production period could be adjusted by adequate formulation of the culture medium.
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PMID:[Effect of the medium composition on the synthesis of protease by Aspergillus sp]. 675 51

The spectral dependence of phycoerythrin synthesis has been studied in a unicellular photautotrophic cyanobacterium, Synechocystis sp. 6701, in which phycoerythrin synthesis alone is under chromatic control. Cells were partially depleted of their phycobiliprotein pigments through nitrate starvation in the light. Addition of nitrate to the culture medium allowed synthesis of phycobiliproteins in the dark. This synthesis occurred at the expense of the glycogen reserve accumulated during the period of nitrate starvation. Monochromatic irradiations of short duration at lambda less than 590 nm induced increased phycoerythrin synthesis during dark incubation. Monochromatic irradiations of short duration at lambda greater than 590 nm prevented this synthesis. These effects were photoreversible. The spectral distribution showed a maximum at 540 nm for the potentiation of phycoerythrin synthesis, and one at 640 nm for its photoreversal.
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PMID:Wavelength modulation of phycoerythrin synthesis in Synechocystis sp. 6701. 676 11


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