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

We have characterized a digitonin-permeabilized cell system for the ATP-dependent degradation of endogenous long-lived proteins. Proteolysis requires Mg2+ and ATP hydrolysis. Other nucleotide triphosphates (CTP, UTP) can partially replace the ATP requirement. The enhanced rate of degradation of long-lived proteins in response to serum starvation is maintained in the permeabilized cell system and can be partially inhibited by lysosomal inhibitors. The maintenance of intracellular architecture and ease of manipulation of soluble components make the permeabilized cell system ideal for studying the proteolysis of both endogenous and exogenous substrates.
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PMID:An ATP-dependent system specific for degradation of long-lived proteins in permeabilized cells. 334 14

Obesity, a well-known phenomenon in Western society, is frequently associated with cardiovascular and endocrine disease. Strokes, myocardial infarction, diabetes and hyperlipidemia are classical reasons for the high mortality and morbidity of overweight people. For this reason, intensive weight-reduction programs have been proposed: low-calorie diets, total starvation, drugs and even surgery. Total starvation and some low-calorie diets are, however, also associated with sudden death, most probably of cardiac origin. Experimental data from our laboratory show that total starvation is accompanied by a severe depletion of magnesium in myocardial tissue. Protein-sparing modified low-calorie diets, however, can protect against this mineral loss even if magnesium supplementation alone cannot obtain this goal. Applying these principles in overweight man show weight reduction without mineral loss or cardiac disturbance. Surgery with 'ileal bypass' procedures gives rise to severe hypomagnesemia and hypocalcemia with tetany and spasmophilia. New procedures, derived from experimental surgery, are 'gastric bypass' and 'gastroplasty'. These methods, only applied in very obese patients (body mass index greater than 40, normal 23-27) show no change in mineral concentrations of calcium and magnesium and no clinical symptoms suggestive for mineral loss. A good, controlled weight-reduction program under strict medical surveillance can, in this way, offer new perspectives in the treatment of one of our most frequent 'culture-induced' diseases.
Magnesium 1987
PMID:Magnesium and obesity: effects of treatment on magnesium and other parameters. 382 Nov 74

Thioacetamide, given intraperitoneally (1.4 mmol/kg body mass) to male Wistar rats 24 h before sacrifice promoted a marked elevation of serum aminotransferases, loss of microsomal cytochrome P-450 content and a significant reduction (about 50%) of the liver plasma membrane enzymatic activities (5'-nucleotidase; K+, Na+- and Mg2+-adenosine triphosphatases; and gamma-glutamyl transferase). Previous starvation for 48 h, immediately prior to thioacetamide administration, strongly potentiated the effects of thioacetamide on the serum, microsomal and liver plasma membrane parameters, while fasting itself did not affect them. The liver plasma membrane damage may be one of the reasons for the cell death in thioacetamide-intoxicated rat livers.
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PMID:The effect of thioacetamide on rat liver plasma membrane enzymes and its potentiation by fasting. 394 71

Cells of Arthrobacter crystallopoietes, harvested during growth as spheres and as rods, were starved by shaking at 30 C in phosphate buffer for 30 days, during which time they maintained 100% viability. Changes in cellular components and the activity of specific enzyme pathways were monitored. A glycogen-like polysaccharide comprised 40% of the dry weight of growing spherical cells and 10% of the dry weight of rod cells. This material was utilized at approximately the same rate, on a percentage basis, during starvation of both cell forms. The rods degraded intracellular protein at approximately twice the rate of the spheres. At the end of 30 days, the rods had degraded 40% and the spheres 20% of their initial content of protein. Ribonucleic acid (RNA) was degraded significantly more rapidly in the rods. After 30 days starvation, 85 and 32% of the initial RNA of rods and spheres, respectively, had been depleted. Magnesium ion followed this same general pattern; the rods lost 65% and the spheres 45% of their initial content during 28 days of starvation. Deoxyribonucleic acid increased by 20% during the first few hours of starvation of both cell forms and then remained constant. The ability of glucose-, succinate-, and 2-hydroxypyridine (2-HP)-grown cells to oxidize glucose remained constant during 14 days of starvation. The ability of succinate-grown cells to oxidize succinate decreased rapidly during the first few hours of starvation to a rate which remained constant for 14 days. Cells adapted to growth on 2-HP completely lost their ability to oxidize this substrate after 3 days starvation.
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PMID:Intracellular substrates for endogenous metabolism during long-term starvation of rod and spherical cells of Arthrobacter crystallopoietes. 547 76

Normal as well as Rous sarcoma virus-infected chicken pectoral and chicken embryo fibroblasts proliferate actively in a plasma containing medium of physiological ion concentrations (Ca2+, 1.2 mM; Mg2+, 0.7 mM). Reduction of medium calcium and magnesium concentrations is necessary to achieve selective quiescence of normal fibroblasts in these cell systems. By contrast, normal chicken heart mesenchymal cells proliferate only sluggishly (one doubling or less during a 6-day period) in a plasma containing medium of physiologic ion concentrations, whereas Rous sarcoma virus-infected heart mesenchymal cells proliferate actively (more than four doublings during an initial 2-day phase of exponential growth). The chicken heart mesenchymal cell system therefore has great potential for studies of the mechanism that initiates cell replication and of the failure in cellular regulatory processes that is responsible for the autonomous initiation of replication of neoplastic cells. From comparison of the chicken heart mesenchymal cell system to dialyzed plasma-based systems in which 3T3 cells tend to proliferative quiescence, it is argued that this proliferative quiescence of 3T3 cells is a result of cell starvation and is not physiologically meaningful.
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PMID:Active proliferation of Rous sarcoma virus-infected, but not normal, chicken heart mesenchymal cells in culture medium of physiological composition. 625 50

Cyclic AMP phosphodiesterase in Klebsiella aerogenes is a soluble cytoplasmic enzyme with an apparent Km of 0.9 mM and a pH optimum of 7.0. It was inhibited by EDTA, Mg2+ and other metal ions. The enzyme activity was inhibited or activated by some nucleotides but not by any metabolite except pyruvate. It was inhibited by the methylxanthines, caffeine, theophylline and methylisobutylxanthine. During starvation or substrate-accelerated death, the enzyme activity remained essentially constant. It is postulated that during substrate-accelerated death the enzyme acts as a drain on the cellular cyclic AMP levels. The cyclic nucleotide concentrations during substrate-accelerated death are proposed to be controlled directly by adenylate cyclase.
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PMID:Characterization of 3': 5' -cyclic AMP phosphodiesterase in Klebsiella aerogenes and its role in substrate-accelerated death. 627 1

The total activity of pyruvate dehydrogenase (PDH) complex in rat hind-limb muscle mitochondria was 76.4 units/g of mitochondrial protein. The proportion of complex in the active form was 34% (as isolated), 8-14% (incubation with respiratory substrates) and greater than 98% (incubation without respiratory substrates). Complex was also inactivated by ATP in the presence of oligomycin B and carbonyl cyanide m-chlorophenylhydrazone. Ca2+ (which activates PDH phosphatase) and pyruvate or dichloroacetate (which inhibit PDH kinase) each increased the concentration of active PDH complex in a concentration-dependent manner in mitochondria oxidizing 2-oxoglutarate/L-malate. Values giving half-maximal activation were 10 nM-Ca2+, 3 mM-pyruvate and 16 microM-dichloroacetate. Activation by Ca2+ was inhibited by Na+ and Mg2+. Mitochondria incubated with [32P]Pi/2-oxoglutarate/L-malate incorporated 32P into three phosphorylation sites in the alpha-chain of PDH; relative rates of phosphorylation were sites 1 greater than 2 greater than 3, and of dephosphorylation, sites 2 greater than 1 greater than 3. Starvation ( 48h ) or induction of alloxan-diabetes had no effect on the total activity of PDH complex in skeletal-muscle mitochondria, but each decreased the concentration of active complex in mitochondria oxidizing 2-oxoglutarate/L-malate and increased the concentrations of Ca2+, pyruvate or dichloracetate required for half-maximal reactivation. In extracts of mitochondria the activity of PDH kinase was increased 2-3-fold by 48 h starvation or alloxan-diabetes, but the activity of PDH phosphatase was unchanged.
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PMID:Reversible phosphorylation of pyruvate dehydrogenase in rat skeletal-muscle mitochondria. Effects of starvation and diabetes. 633 93

The many causes of clinical magnesium deficiency can be placed into 2 categories: diminished intake of magnesium, and enhanced losses of magnesium, either through the gastrointestinal tract or through the kidneys. Examples of the first category include alcoholism, starvation, anorexia due to neoplastic disease and/or chemotherapy. Examples of the second category include severe diarrhoeal states, gastrointestinal fistulae, malabsorption, diuretic therapy and gentamicin therapy. Estimates of the prevalence of clinical hypomagnesaemia range from 6 to 11% in hospitalised patients. Serum predictors of associated clinical magnesium depletion include hypokalaemia (42%), hyponatraemia (23%), hypophosphataemia (22%) and hypocalcaemia (20%). Experimental and clinical observations strongly support the view that magnesium and potassium are closely linked at the cellular level. Magnesium has been demonstrated to be important in cell energetics (Mg++-activated ATPase), in maintenance of the integrity of cell membranes, retardation of cell loss of potassium, as well as enhancing repletion of cell potassium. While translation of these experimental observations into clinical terms encompasses a wide spectrum of illnesses, there is special relevance in considering the role of magnesium in repletion and maintenance of cell potassium in 2 clinical instances: (a) patients treated with digitalis and diuretics; and (b) hypertensive patients. In these types of patients not only potassium but also magnesium should be administered together to avoid the problem of cell potassium depletion and refractory potassium repletion associated with coexisting and uncorrected magnesium depletion.
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PMID:Magnesium deficiency. Causes and clinical implications. 649 96

The effects of Mg2+ and Ca2+ deprivation on survival and growth of normal and transformed cultured cells were studied. Normal fibroblast from several origins (mouse, hamster and human) did not grow in 2 microM Mg2+ medium, whereas transformed fibroblasts (mouse and rat) and tumor cells of other types (mouse adrenocortical and rat glial cells) grew optimal. All transformed or tumorogenic cells that showed low growth requirement for Mg2+ were able to develop colonies in agarose suspension cultures, i.e., were anchorage-independent fo growth. Mg2+ deprivation of normal cells did not lead to cell cycle arresting at G0/G1 and cell death accounts for the limited growth of these cells in medium containing low Mg2+ concentration. Contrary to Mg2+, starvation for serum or for Ca2+ caused normal cells to undergo cell cycle arrest at the G0/G1 phase. During the progressive spontaneous transformation of Swiss mouse 3T3 fibroblasts, the decrease in growth requirements for Mg2+ and Ca2+ do not occur at the same time. The requirement for external Ca2+ lowers before the onset of anchorage-independent growth while the Mg2+ requirement only decreases after cells become anchorage-independent. Therefore the reductions in growth requirement for Mg2+ and Ca2+ that take place in cell transformation are not linked events.
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PMID:Ca2+ and Mg2+ requirements for growth are not concomitantly reduced during cell transformation. 670 40

The degradation of three types of anomalous proteins, e. g. those containing the arginine analog kanavanine; polypeptides synthesized in the presence of puromycin (100 micrograms/ml) under slight inhibition of total translation, and polypeptides synthesized under amino acid deficiency, was studied. In order to measure the rate of proteolysis, the E. coli cells were labelled for 5 min with [14C]-phenylalanine and then transferred to a complete medium. The loss of TCA-insoluble material was taken as a measure of proteolysis. While the normal total protein of E. coli cells was degraded at the rate of 2--8% per hour, the canavanine-containing proteins were degraded at the rate of 30--40% per hour. The polypeptides synthesized in the presence of puromycin were degraded at the rate of 10--15% per hour, while the polypeptides formed under amino acid starvation--at the rate of 7--8% per hour. The rate of proteolysis of canavanine-containing polypeptides was two times lower under inhibition of translation by chloramphenicol, tetracycline of kasugamicin, while the rate of degradation of two other types of anomalous polypeptides was significantly increased. Tetracycline at concentrations significantly exceeding those sufficient for maximal inhibition of translation, practically completely repressed the proteolysis of canavanine-containing proteins. No such tetracycline activity was observed in the presence of 20 mM Mg2+, which was assumed to be dependent on the complexon-forming ability of the antibiotic.
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PMID:[Role of protein synthesis in the process of degradation of anomalous proteins in Escherichia coli cells]. 701 90


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