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

The regulation of dihydrodipicolinate synthase (EC 4.2.1.52) and aspartate kinase (EC 2.7.2.4) was studied in Bacillus subtilis 168. Starvation for lysine gave depression of one aspartate kinase isoenzyme but not of dihydrodipicolinate synthase. Strains resistant to growth inhibition by the lysine analogue thiosine exhibited constitutively derepressed synthesis of one aspartate kinase isoenzyme but had normal levels of dihydrodipicolinate synthase. The data provide strong evidence that lysine is not the signal for derepression of dihydrodipicolinate synthase. Nevertheless, dihydrodipicolinate synthase specific activity increased during sporulation, and it is suggested that this increase may result, in part, from resistance to proteolysis of that enzyme.
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PMID:Regulation of dihydrodipicolinate synthase and aspartate kinase in Bacillus subtilis. 16 19

Aspartokinase II from Bacillus subtilis was shown by immunochemical methods to be regulated by degradation in response to starvation of cells for various nutrients. Ammonium starvation induced the fastest aspartokinase II decline (t1/2 = 65 min), followed by amino acid starvation (t1/2 = 80 min) and glucose limitation (t1/2 = 120 min). Loss of enzyme activity was closely correlated with the disappearance of the alpha subunit; degradation of the beta subunit was somewhat delayed or slower under some conditions. Pulse-chase experiments demonstrated that aspartokinase II was stable during exponential growth; the synthesis of the enzyme rapidly declined in response to nutrient exhaustion. The degradation of aspartokinase II was interrupted by inhibitors of energy production and protein synthesis but was not changed in a mutant lacking a major intracellular protease. Mutants lacking a normal stringent response displayed only a slight decrease in the rate of aspartokinase II degradation, even though aspartate transcarbamylase was degraded more slowly in the same mutant cells. These results indicate that although energy-dependent degradation of biosynthetic enzymes is a general phenomenon in nutrient-starved B. subtilis cells, the degradation of specific enzymes probably involves different pathways.
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PMID:Aspartokinase II from Bacillus subtilis is degraded in response to nutrient limitation. 216 95

Some of the early enzymes in the lysine-biosynthetic pathway also function for dipicolinic acid synthesis in sporulating Bacillus cereus T. 1. The first enzyme, aspartokinase, loses its sensitivity to feedback inhibition by lysing. This change occurs before the time of dipicolinic acid synthesis but at a time when diaminopimelic acid is required for spore cortex formation. 2. A possible regulatory change at a branch point in the pathway was studied by examining the properties of a key enzyme, dihydrodipicolinic acid reductase. No alteration in the feedback sensitivity or sedimentation rate of this enzyme could be detected during sporulation. 3. Two mutants producing heat-sensitive spores were analysed. Both produced spores that contained decreased amounts of dipicolinic acid. Although neither was a lysine auxotroph, they both had greatly decreased activities of certain lysine-biosynthetic enzymes in sporulating cells. 4. Starvation of cells for calcium also results in the production of spores that are heat-sensitive and contain less dipicolinic acid than the control. A decreased content of one of the lysine-biosynthetic enzymes, dihydrodipicolinic acid synthetase, in calcium-starved cells could account for the lower concentration of dipicolinic acid in the spores.
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PMID:Regulation of dipicolinic acid biosynthesis in sporulating Bacillus cereus. Characterization of enzymic changes and analysis of mutants. 462 86

The relationship between aspartokinase activity and fruiting body formation in Myxococcus xanthus was investigated. Two required amino acids, methionine and isoleucine, which stimulated the enzyme in vitro also inhibited fruiting body formation when added to 0.1% Casitone agar. Threonine, a potent feedback inhibitor of the aspartokinase, completely reversed the effects of methionine and isoleucine both on enzyme activity and fruiting body formation. A mutant, M. xanthus FB-S, which had the unusual property of forming fruiting bodies on 1.0% Casitone agar, also exhibited an altered regulation of aspartokinase activity. Spermidine, which is a strong stimulator of the enzyme in vitro, interfered with the developmental cycle of both M. xanthus FB and FS-S. During glycerol induction of myxospores the level of aspartokinase dropped more than 75% during the first hour. These data indicate a strong correlation between aspartokinase activity and the induction of the developmental cycle in M. xanthus. It is suggested that the decrease in aspartokinase activity results in diaminopimelic acid starvation, blockage of cell wall growth, and subsequent induction of the developmental cycle.
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PMID:Aspartokinase activity and the developmental cycle of Myxococcus xanthus. 471 18

Further studies on the expression of the two aspartokinase activities in Bacillus bovis are presented. Aspartokinase I (previously shown to be inhibited and repressed by lysine) was found to be repressed by diaminopimelate in the wild-type strain. However, in a mutant unable to convert diaminopimelate to lysine, starvation for lysine resulted in an increase in aspartokinase I activity. Thus, lysine itself or an immediate metabolite was the true effector of repression. Aspartokinase II (previously shown to be inhibited by lysine plus threonine) was repressed by threonine. Studies with the parent strain and auxotrophs inidicated that only threonine or an immediate metabolite of threonine was involved in this repression. Methionine and isoleucine were not effectors of any of the detected aspartokinase activities. Apart from inhibition and repression controls, a third as yet undefined regulatory mechanism operated to decrease the levels of both aspartokinases as growth declined, even in mutants in which repression control was absent. In thiosine-resistant, lysine-excreting mutants with elevated levels of aspartokinase, the increase in activity could always be attributed to one enzyme or the other, never both. The existence of separate structural genes for each aspartokinase is therefore suggested.
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PMID:Regulation of lysine- and lysine-plus-threonine-inhibitable aspartokinases in Bacillus brevis. 624 20

Development of multicellular fruiting bodies of Myxococcus xanthus can be induced by limitation of any of a number of different classes of amino acids. Investigated were amino acids that wild-type strains of M. xanthus are unable to synthesize (isoleucine, leucine, and valine), can synthesize at a low rate (phenylalanine), or can normally synthesize at an adequate rate (tryptophan and serine). In general, gradual rather than abrupt starvation for an essential amino acid was required for the induction of fruiting. Perhaps gradual starvation in general minimizes antagonism between amino acids present in the medium, as was documented for valine starvation. The previously reported induction of fruiting by a high concentration of threonine was shown to be specifically reversed by lysine. Threonine addition may starve cells for lysine by feedback inhibition of aspartokinase activity. Starvation for carbon-energy sources or inorganic phosphate also induced fruiting. As in other bacteria, amino acid starvation of M. xanthus leads to increases in cellular guanosine polyphosphate, usually consisting of large increases in the amount of guanosine pentaphosphate with smaller increases in the level of guanosine tetraphosphate. Guanosine polyphosphate accumulation is thus shown to be correlated with nutritional conditions that induce fruiting, and therefore may serve as an intracellular signal to trigger cells to end vegetative growth and initiate fruiting body development.
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PMID:Guanosine pentaphosphate and guanosine tetraphosphate accumulation and induction of Myxococcus xanthus fruiting body development. 676 42