Repression of enzymes of nitrogen catabolism by methylammonium and caesium chloride in strains of Aspergillus nidulans insensitive to ammonium repression.
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Hysteresis, oscillations, and pattern formation in realistic biochemical systems governed by P.D.E.s are considered from both numerical and mathematical points of view. Analysis of multiple steady states in the case of hysteresis, and bifurcation theory in the cases of oscillations and pattern formation, account for the observed numerical results. The possibility to realize these systems experimentally is their main interest, thus bringing further arguments in favor of theories explaining basic biological phenomena by diffusion and reaction.
The morphological alterations of hepatocytes of golden ide, Leuciscus idus melanotus, following adaptation to low and high temperatures (14 and 28 degrees C) were investigated by means of light and electron microscopy. The temperature-dependent behaviour of peroxisomes was visualized cytochemically with the alkaline diaminobenzidine medium; the morphological studies were supplemented by the biochemical determination of catalase activity. Cold adaptation of ide hepatocytes is manifested by proliferation and stacking of endoplasmic reticulum, an enhanced secretory activity of Golgi fields and a higher number of peroxisomes as compared with the warm-adapted animals. The latter organelles are characterized by a marked heterogeneity in size, shape and catalase activity, and by a more intimate association with mitochondria and endoplasmic reticulum. The occurrence of small peroxisomal profiles is restricted to lower temperature. Catalase activity can be shown both cytochemically and biochemically to increase during cold adaptation. Whereas the number of mitochondria seems to be unaffected by thermal adaptation, stacking of mitochondria as well as the formation of intramitochondrial membrane piles indicate cold-adaptive processes. A feature typical of warm-adaptation is the formation of membrane-glycogen complexes, which may represent the morphological expression of enhanced carbohydrate metabolism documented in a decreased storage of glycogen at 28 degrees C. At 28 degrees C lipid is the predominant storage product. These findings indicate that fish liver is well-suited to serve as a model for the analysis of the interaction of environmental temperature conditions and hepatic morphology.
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Tumor lysis syndrome refers to the metabolic disturbances (hyperuricemia, hyperphosphatemia, hyperkalemia, and hypocalcemia) associated with lymphoproliferative malignancies which occur secondary to cell lysis. In some patients, tumor lysis results in acute renal failure. The nature and severity of the metabolic alterations are variable and may be influenced by the timing and intensity of chemotherapy, the magnitude of cell lysis, and the general condition of the patient with respect to hydration and glomerular filtration rate. Not only do hyperuricemia and hyperphosphatemia result from tumor lysis syndrome, they also contribute to oliguric acute renal failure in patients with tumor lysis. The pathogenesis of tumor lysis syndrome and current therapeutic strategies are discussed.
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The uptake rate of uric acid into liver slices of the Dalmatian dog was found to be significantly lower compared with that in the beagle. Since there was no difference in the hepatic uricase activity between the two breeds, the abnormality of uric acid metabolism in the Dalmatian dog is considered to result from a defective hepatic transport system for uric acid.
A Phaseolus vulgaris uricase II cDNA clone has been isolated and sequenced. Comparison on the nucleotide level between this clone and the soybean uricase II clone revealed 88.8% identity. The in situ hybridization technique was used to follow the expression pattern in developing root nodules of Phaseolus vulgaris. The uricase II transcripts were localized only in the uninfected cells of the central tissue and mainly in the periphery of the cell. Uricase II mRNA is first detected in nodules 12 days after infection. A maximum level of transcripts is reached in 21-day-old nodules, followed by a considerable reduction in 28-day-old nodules.
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