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1.
Abstract. Cell aggregation in Dictyostelium discoideum is a chemotactic process mediated by cyclic adenosine monophosphate (CAMP), which is detected by cell surface receptors. The cAMP signal is degraded by cAMP phosphodiesterase. The possibility that cAMP signals are also used for cell communication in the multicellular stages was studied by determining whether the cAMP receptors, which are essential for signal transduction, continue to function in these stages. During slug migration, the number of binding sites per cell decreases to about 15% of the maximum level acquired during aggregation. At the onset of fruiting body formation, a three- to Four-Fold increase in cAMP binding activity occurs. This increase coincides with an increase in cAMP phosphodiesterase. Both phenomena suggest that cell-cell communication mediated by cAMP is used during culmination. During both slug migration and early culmination, the prestalk cells exhibit about twice as much binding activity as the prespore cells. 相似文献
2.
The histone H1°/H5 variant and terminal differentiation of cells during development of Xenopus laevis 总被引:1,自引:0,他引:1
Antoon F.M. Moorman Piet A.J. de Boer Rob Charles Wouter H. Lamers 《Differentiation; research in biological diversity》1987,35(2):100-107
The maintenance of the differentiated condition is supposed to be associated with the presence of a histone of the H1(0)/H5 subclass. If the H1(0)/H5 variant has an important role in differentiation distinct from that of H1, it should display differential expression in time and position during development. Here we report that this prediction is verified during Xenopus laevis development, in which tadpoles exhibit a very characteristic, developmentally regulated pattern of histone H1(0)/H5 expression that is different for the derivatives of each embryonic germ layer. However, the pattern of appearance of this variant during development does not reflect a simple correlation between its presence and the state of differentiation. Therefore, these results are pertinent to current ideas on differentiation and the involvement of lysine-rich histones in the repression of eukaryotic genes. 相似文献
3.
Wouter J. Middelhoven Heleen de Kievit André L. Biesbroek 《Antonie van Leeuwenhoek》1985,51(3):289-301
Yeast strains utilizing uric acid, adenine, monoamines or diamines as sole source of carbon and energy were isolated from
several soil samples by the enrichment culture method. The most common species wasTrichosporon cutaneum. Strains ofCandida catenulata, C. famata, C. parapsilosis, C. rugosa, Cryptococcus laurentii, Stephanoascus ciferrii andTr. adeninovorans were also isolated. All strains utilizing uric acid as sole carbon source utilized some primaryn-alkyl-l-amines hydroxyamines or diamines as well. The ascomycetous yeast strains showing these characteristics all belonged
to species known to assimilate hydrocarbons. Type strains of hydrocarbon-positive yeast species which were not found in the
enrichment cultures generally assimilated putrescine, some type strains also butylamine or pentylamine, but none assimilated
uric acid. Methanol-positive species were not isolated. Type strains of methanol-positive and of hydrocarbon-negative species
did not assimilate uric acid, butylamine or putrescine. Assimilation of putrescine as sole source of carbon and energy may
be a valuable diagnostic criterion in yeast taxonomy. 相似文献
4.
Zonal heterogeneity of rat hepatocytes in the in vivo uptake of 17 nm colloidal gold granules 总被引:1,自引:0,他引:1
The in vivo uptake in hepatocytes of intravenously injected colloidal gold granules with a diameter of 17 nm or 79 nm and coated with bovine serum albumin or with polyvinyl-pyrrolidone was studied. Irrespective of coating only the 17 nm granules were taken up in hepatocytes. Perivenous hepatocytes did take up much more gold granules than periportal hepatocytes. The gold granules were found in lysosomes around bile canaliculi. Two hours after injection hepatocytes contained the maximal amount of granules. At least a portion of the granules was discharged into the bile. The observed zonal gradient in the uptake of 17 nm gold granules might be caused by the greater supply of granules to the perivenous hepatocytes as a combined result of the higher porosity of the endothelial lining and the smaller number of Kupffer cells with a low endocytic activity in this zone. 相似文献
5.
Summary Male and female rat liver were studied during post-natal development. A correlation was found between biochemically determined hydroxylations and enzymhisto-chemically determined NADPH-nitro-BT reductase and Naphthol-AS-D esterase. No correlation was found between glucose-6-phosphate dehydrogenase or iso-citric acid dehydrogenase activity and hydroxylations. The difference in hydroxylating capacity between male and female rats may be caused by the fact that the number of cells with hydroxylating activity in the liver lobule, as judged by the NADPH-nitro-BT reductase and Naphthol-AS-D esterase activity, is higher in male than in female rats.List of Abbreviations NADH
reduced nicotinamide adenine dinucleotide
- NADPH
reduced nicotinamide adenine dinucleotide phosphate
- G6PD
glucose-6-phosphate dehydrogenase
- ICD
iso-citric acid dehydrogenase
- G6Pase
glucose-6-phosphatase
- NADPH
-nitro-BT red
- NADPH
Nitro-blue tetrazolium reductase
- SDH
succinic acid dehydrogenase
- TCA
trichloracetic acid 相似文献
6.
Wouter J. Middelhoven Alex Coenen Bart Kraakman Maarten D. Sollewijn Gelpke 《Antonie van Leeuwenhoek》1992,62(3):181-187
The imperfect ascomycetous yeastsCandida parapsilosis andArxula adeninivorans degraded 3-hydroxybenzoic acid via gentisate which was the cleavage substrate. 4-Hydroxybenzoic acid was metabolized via protocatechuate. No cleavage enzyme for the latter was detected. In stead of this NADH- and NADPH-dependent monooxygenases were present. In cells grown at the expense of hydroquinone and 4-hydroxygenzoic acid, enzymes of the hydroxyhydroquinone variant of the 3-oxoadipate pathway were demonstrated, which also took part in the degradation of 2,4-dihydroxybenzoic acid byC. parapsilosis.Abbreviations HHQ
Hydroxyhydroquinone (1,2,4-trihydroxybenzene)
- GSH
reduced Glutathione 相似文献
7.
Instar-specific mortalities of Daphnia hyalina and D.cucullatawere studied from May 19 to September 29, 1988 in combinationwith invertebrate predator and phytoplankton abundance. Simultaneouslife-table experiments were conducted under semi-natural conditionsin the laboratory to estimate juvenile mortality in a predator-freeenvironment. Juvenile mortality by predation was calculatedas the difference between juvenile mortality in the field andin the experiments and was the most important factor for thedifferences in abundance of the two species. For D.hyalina juvenilemortality was higher in early summer and probably caused byselective predation by Chaoborus flavicans. Predation by Leptodorakindtii was probably more important during the rest of the summer.Estimated mortality by predation adequately explained juvenilemortality, except for a 3-week period in August. Decreasingflagellate densities in July were accompanied by increased juvenilemortalities of D.hyalina and D.cucullata in the life-table experimentsin August and coincided with a Daphnia population decrease. 相似文献
8.
9.
Willie J. C. Geerts Wouter H. Lamers Antoon F. M. Moorman 《The Histochemical journal》1993,25(4):280-290
Summary Using antibodies against the fetal and adult forms of - and -globin, it has been shown that erythropoiesis in the para-aortic foci (PAF) constitutes a major species-specific difference between chicken and quail embryos. In quail embryos, para-aortic foci are rare, small and rather heterogeneous with regard to their erythropoietic and haemopoietic cell composition. In contrast, the PAFs in chicken embryos are abundant and consist of large numbers of erythropoietic cells.In both species a time difference (approximately 1 day) is observed between the first expression of the fetal - and -globin and the adult - and -globin in erythropoietic cells. Adult erythropoiesis in both species can be detected first in the stalk of the yolk sac; this is similar to the situation in mammalian and amphibian species. From this time onward the number of circulating adult erythrocytes increases steadily. Whereas in chicken, large intraembryonic foci that can serve as sources for these adult cells arise concomitantly, no such foci can be detected in quail embryos, suggesting that the quail yolk sac is a major source for these adult red blood cells. 相似文献
10.
Production of 6-Phenylacetylene Picolinic Acid from Diphenylacetylene by a Toluene-Degrading Acinetobacter Strain
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Jim C. Spain Shirley F. Nishino Bernard Witholt Loon-Seng Tan Wouter A. Duetz 《Applied microbiology》2003,69(7):4037-4042
Several strategies for using enzymes to catalyze reactions leading to the synthesis of relatively simple substituted picolinic acids have been described. The goal of the work described here was to synthesize a more complex molecule, 6-phenylacetylene picolinic acid [6-(2-phenylethynyl)pyridine-2-carboxylic acid], for use as a potential endcapping agent for aerospace polymers. We screened 139 toluene-degrading strains that use a variety of catabolic pathways for the ability to catalyze oxidative transformation of diphenylacetylene. Acinetobacter sp. strain F4 catalyzed the overall conversion of diphenylacetylene to a yellow metabolite, which was identified as a putative meta ring fission product (2-hydroxy-8-phenyl-6-oxoocta-2,4-dien-7-ynoic acid [RFP]). The activity could be sustained by addition of toluene at a flow rate determined empirically so that the transformations were sustained in spite of the fact that toluene is a competitive inhibitor of the enzymes. The overall rate of transformation was limited by the instability of RFP. The RFP was chemically converted to 6-phenylacetylene picolinic acid by treatment with ammonium hydroxide. The results show the potential for using the normal growth substrate to provide energy and to maintain induction of the enzymes involved in biotransformation during preliminary stages of biocatalyst development. 相似文献