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

Starved cells of Candida utilis accumulated Zn2+ by two different processes. The first was a rapid, energy- and temperature-independent system that probably represented binding to the cell surface. The cells also possessed an energy-, pH-, and temperature-dependent system that was capable of accumulating much greater quantities of the cation than the binding process. The energy-dependent system was inhibited by KCN, Na2HAsO4, m-chlorophenyl carbonylcyanide hydrazone, N-ethylmaleimide, EDTA and diethylenetriaminepenta-acetic acid. The system was specific inasmuch as Ca2+, Cr3+, Mn2+, Co2+ or Cu2+ did not compete with, inhibit, or enhance the process, Zn2+ uptake was inhibited by Cd2+. The system exhibited saturation kinetics with a half-saturation value of 1.3 muM and a maximum rate of 0.21 (nmol Zn2+) min(-1) (mg dry wt(-1)) at 30 degrees C. Zn2+ uptake required intact membranes since only the binding process was observed in the presence of nystatin, toluene, or sodium dodecyl sulphate. Cells did not exchange recently accumulated toluene, or sodium dodecyl sulphate. Cells did not exchange recently accumulated 65Zn following the addition of a large excess of non-radioactive Zn2+. Similarly, cells pre-loaded with 65Zn did not lose the cation during starvation, and efflux did not occur when glucose and exogenous Zn2+ were supplied after the starvation period. Efflux was only observed after the addition of toluene or nystatin, or when cells were heated to 100 degrees C. Cells fed a large quantity of Zn2+ contained a protein fraction resembling animal cell metallothionein. In batch culture, cells of C. utilis accumulated Zn2+ only during the lag phase and the latter half of the exponential-growth phase.
J Gen Microbiol 1976 May
PMID:Accumulation and storage of Zn2+ by Candida utilis. 0 25

It had previously been held that chlorate is not itself toxic, but is rendered toxic as a result of nitrate reductase-catalysed conversion to chlorite. This however cannot be the explanation of chlorate toxicity in Aspergillus nidulans, even though nitrate reductase is known to have chlorate reductase activity. Among other evidence against the classical theory for the mechanism of chlorate toxicity, is the finding that not all mutants lacking nitrate reductase are clorate resistant. Both chlorate-sensitive and resistant mutants lacking nitrate reductase, also lack chlorate reductase. Data is presented which implicates not only nitrate reductase but also the product of the nirA gene, a positive regulator gene for nitrate assimilation, in the mediation of chlorate toxicity. Alternative mechanisms for chlorate toxicity are considered. It is unlikely that chlorate toxicity results from the involvement of nitrate reductase and the nirA gene product in the regulation either of nitrite reductase, or of the pentose phosphate pathway. Although low pH has an effect similar to chlorate, chorate is not likely to be toxic because it lowers the pH; low pH and chlorate may instead have similar effects. A possible explanation for chlorate toxicity is that it mimics nitrate in mediating, via nitrate reductase and the nirA gene product, a shut-down of nitrogen catabolism. As chlorate cannot act as a nitrogen source, nitrogen starvation ensues.
Mol Gen Genet 1976 Jul 23
PMID:Chlorate toxicity in Aspergillus nidulans. Studies of mutants altered in nitrate assimilation. 0 97

Synthesis of glutamine synthetase (GS) in anaerobic batch cultures of Escherichia coli was repressed when excess NH4+ was available, but derepressed during growth with a poor nitrogen source. In wild-type bacteria there was only a weak inverse correlation between the activities of GS and glutamate dehydrogenase (GDH) during growth in various media. No positive correlations were found between the activities of GS and nitrite reductase, or between GS and cytochrome c552: both of these proteins were synthesized normally by mutants that contained no active GS. Although activities of GS and GDH were low in two mutants that are unable to synthesize cytochrome c552 or reduce nitrite because of defects in the nirA gene, the nirA defect was separated from the GS and GDH defects by transduction with bacteriophage P1. Attempts to show that catabolite repression of proline oxidase synthesis could be relieved during NH4+ starvation also failed. It is, therefore, unlikely that nitrite reduction or proline oxidation by E. coli are under positive control by GS protein. The regulation of the synthesis of enzymes for the utilization of secondary nitrogen sources in E. coli, therefore, different from that in Klebsiella aerogenes, but is similar to that in Salmonella typhimurium.
J Gen Microbiol 1977 Feb
PMID:Lack of a regulatory function for glutamine synthetase protein in the synthesis of glutamate dehydrogenase and nitrite reductase in Escherichia coli K12. 1 79

Induced wildtype cells of A. nidulans rapidly lost NADPH--linked nitrate reductase activity when subjected to carbon and or nitrogen starvation. A constitutive mutant at the regulatory gene for nitrate reductase, nir Ac 1, rapidly lost nitrate reductase activity upon carbon starvation. This loss of activity is thought to be due to a decrease in the NADPH concentration in the cells. Cell free extracts from wildtype cells grown in the presence of nitrate, rapidly lost their nitrate reductase activity when incubated at 25 degrees C. NADPH prevented this loss of activity. Wildtype cells grown in the presence of nitrate and urea have a higher initial NADPH:NADP+ ratio and cell free extracts from such cells lost their nitrate reductase activity slower than extracts of cells grown with nitrate alone. The Pentose Phosphate Pathway mutant, pppB-1, had a lower NADPH concentration compared with the wildtype grown under the same conditions and cell free extracts lost their nitrate reductase activity more rapidly than the wildtype. Cell free extracts of nirAc-1 and a non-inducible mutant for nitrate reductase, nirA- -14, upon incubation lost little of their nitrate reductase activity.
Mol Gen Genet 1977 Apr 29
PMID:In vivo and in vitro studies of nitrate reductase regulation in Asperillus nidulans. 1 26

Repression of biosynthetic enzyme synthesis in Pseudomonas putida is incomplete even when the bacteria are growing in a nutritionally complex environment. The synthesis of four of the enzymes of the arginine biosynthetic pathway (N-acetyl-alpha-glutamokinase/N-acetylglutamate-gamma-semialdehyde dehydrogenase, ornithine carbamoyltransferase and acetylornithine-delta-transaminase) could be repressed and derepressed, but the maximum difference observed between repressed and derepressed levels for any enzyme of the pathway was only 5-fold (for ornithine carbamoyltransferase). No repression of five enzymes of the pyrimidine biosynthetic pathway (aspartate carbamoyltransferase, dihydro-orotase, dihydro-orotate dehydrogenase, orotidine-5'-phosphate pyrophosphorylase and orotidine-5'-phosphate decarboxylase) could be detected on addition of pyrimidines to minimal asparagine cultures of P. putida A90, but a 1-5- to 2-fold degree of derepression was found following pyrimidine starvation of pyrimidine auxotrophic mutants of P. putida A90. Aspartate carbamoyltransferase in crude extracts of P. putida A90 was inhibited in vitro by (in order of efficiency) pyrophosphate, CTP, UTP and ATP, at limiting but not at saturating concentrations of carbamoyl phosphate.
J Gen Microbiol 1976 Feb
PMID:Regulation of arginine and pyrimidine biosynthesis in Pseudomonas putida. 17 12

Cell-free extracts prepared from spherical and rod-shaped cells of Arthrobacter crystallopoietes were assayed for enzymes during various periods of starvation. The level of NADH oxidase dropped to 20 and 30%, respectively, in spherical and rod-shaped cells during the first 1 to 2 days of starvation and then remained constant for 9 days. Catalase activity decreased continuously and reached a low level in 9 days. Enzymes involved in glucose metabolism and the tricarboxylic acid cycle were stable for the duration of the experiment (about 1 week). Succinic dehydrogenase, fumarase and aconitase were stable during 21 days of starvation, which is the longest time enzymes have been shown to be stable in any bacterium under conditions of total starvation.
J Gen Microbiol 1976 May
PMID:Stability of enzymes in starving Arthrobacter crystallopoietes. 18 Feb 37

A freshwater Spirillum sp., which apparently belongs to a niche of low nutritional status (Matin & Veldkamp, 1978), accumulated poly-beta-hydroxybutyric acid (PHB) during lactate-limited growth in continuous culture. The PHB content varied in a complex manner with the dilution rate (D), but was greatest at the lowest D value examined: about 18% (w/w) at D = 0.025 h-1. It is not known what mechanism accounted for PHB accumulation during carbon-limited growth. The resistance of cultures of Spirillum sp. to starvation after growth at various D values was compared with that of a Pseudomonas sp. which appears to belong to relatively richer environments (Matin & Veldkamp, 1978) and does not accumulate PHB. In Spirillum sp., resistance correlated directly with the PHB content of the culture subjected to starvation, whereas in Pseudomonas sp. it increased with RNA content. Further, after growth at D = 0.03 to 0.05 h-1, the Spirillum sp. was much more resistant to starvation than was the Pseudomonas sp. Since the microflora of oligotrophic environments are probably often subjected to starvation conditions, PHB accumulation by Spirillum sp. during growth in such environments may assist survival. PHB in Spirillum sp. was rapidly degraded during starvation but it had no sparing effect on RNA degradation. It is not known how PHB enhanced resistance to starvation.
J Gen Microbiol 1979 Jun
PMID:Selective advantage of a Spirillum sp. in a carbon-limited environment. Accumulation of poly-beta-hydroxybutyric acid and its role in starvation. 22 10

The synthesis of the arginine pathway carbamoylphosphate synthase (CPSase A) of Saccharomyces cerevisiae is subject to two control mechanisms. One mechanism is specific for CPSase A and is exerted by arginine; it probably involves a repressor-operator type of interaction. This "specific" mechanism regulates the expression of gene cpaI coding for the small "glutaminase" subunit of CPSase A but has little influence on the production of the large subunit of the enzyme, a product of gene cpaII. This large component, which alone has no biological significance, accumulates freely under conditions of arginine repression. The second mechanism is general: it controls enzyme synthesis in a number of amino acid biosynthetic pathways in addition to the arginine sequence. Two types of evidence that this "general" mechanism participates in the control of CPSase A synthesis are presented: (1) Derepression upon starvation for any amino acid of which the synthesis is subject to this general control; and (2) repression during growth in amino acid-rich medium. In contrast to the specific mechanism, the "general" mechanism regulates the expression of both the cpaI and cpaII genes.
Mol Gen Genet 1979 Jul 13
PMID:Dual regulation of the synthesis of the arginine pathway carbamoylphosphate synthase of Saccharomyces cerevisiae by specific and general controls of amino acid biosynthesis. 22 37

The 'relaxed particles' formed during methionine starvation of Escherichia coli A19 (Hfr rel met rns) have been isolated by large-scale rate-zonal density gradient ultracentrifugation. The proteins and rRNA species associated with these particles have been examined. The rRNA species present are precursor and mature forms of 16S and 23S rRNA. The bulk of the rRNA which accumulates during starvation is found within the particles. The proteins prepared directly from the particles give strong multiple immunoprecipitates with antisera specific to 30S and 50S ribosomal proteins. The soluble proteins, prepared and examined in the same manner, do not give this immunological reaction. Two-dimensional electrophoresis patterns of the proteins from the particles show that the proteins co-migrate with proteins from 30S and 50S ribosomes and are entirely dissimilar to the proteins prepared by the same methods from the soluble fraction of the cells. On the basis of these and other observations, it is concluded that the 'relaxed particles' are not artefacts but are arrested ribosome precursors containing both rRNA and certain ribosomal proteins. The free pool of ribosomal proteins is low in exponential-phase cells and is not significantly increased by a 2 h period of starvation for glucose. The implications of these observations concerning the proteins associated with 'relaxed' and 'chloramphenicol particles' are discussed in raltion to ribosome biogenesis and the stabilization of rRNA.
J Gen Microbiol 1977 Jan
PMID:The nature of the proteins present in the 'relaxed particles' from methionine-starved Escherichia coli A19 (Hfr rel met rns). 31 97

Mutants in the spo T gene have been isolated as stringent second site revertants of the relC mutation. These show varying degrees of the characteristics associated with the spoT1 gene, viz relative amount and absolute levels of both pppGpp and ppGpp and the decay rate of the latter. The entry of 3H-guanosine into GTP and ppGpr pools in spoT+ and spoT1 cells either growing exponentially or during amino acid starvation was determined, and the rate of ppGpp synthesis and its decay constant calculated. During exponential growth the ppGpp pool is 2-fold higher, its decay constant 10-fold lower, and its synthesis rate 5-fold lower in spoT- than in spoT+ cells; during amino acid starvation the ppGpp pool is 2-fold higher, its decay constant 20-fold lower, and its synthesis rate 10-fold lower in spoT than in spoT+ cells. In one of the "intermediate" spoT mutants the rate of entry of 3H-guanosine into GTP, ppGpp and pppGpp was measured during amino acid starvation. The data form the basis of a model for the interconversion of the guanosine nucleotides in which the flow is: GDP leads to GTP leads to pppGpp leads to ppGpp leads to Y. Calculations of the rates of synthesis and conversion of pppGpp and ppGpp under various conditions in various spoT+ and spoT- strains indicate that the ppGpp concentration indirectly controls the rate of pppGpp synthesis.
Mol Gen Genet 1977 Jan 07
PMID:Interaction of alleles of the relA, relC and spoT genes in Escherichia coli: analysis of the interconversion of GTP, ppGpp and pppGpp. 31 45


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