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1.
2.
Phenotypic dissections of the Blastocladiella emersonii zoospore's developmental choice 总被引:1,自引:0,他引:1
A developmentally homogeneous neural crest cell population has been used to assay the role of environmental factors in regulating crest cell differentiation. If cultured on tissue culture plastic, virtually all of the cells of this population differentiate into melanocytes. In contrast, when these cells are cultured for 3 or more days on substrata “conditioned” by somite fibroblasts, the proportion of cells undergoing melanogenesis decreased and the proportion expressing formaldehyde-induced fluorescence (FIF), characteristic of catecholamine-containing cells, increased. For a limited period of culture on somite-conditioned substrata, some cells in the population exhibit both pigment granules and fluorescence. Collagen-coated substrata decreased the number of cells that formed pigment but did not stimulate FIF. In contrast, optimum doses of exogenous cellular fibronectin mimicked the effect of somite-conditioned substrata, suppressing melanogenesis and promoting FIF. Glycosaminoglycan-derivatized substrata (i.e., hyaluronic acid, various chondroitin sulfate preparations, and heparin) did not alter the differentiative homogeneity of the cultured crest cell populations. The choice and expression of phenotype by some members of a cultured crest cell population can, therefore, be affected by environmental stimuli provided in the form of certain substrate-attached macromolecules. We suggest that optimal concentrations of some extracellular matrix components produced by embryonic tissue and normally encountered by migrating crest cells may elicit the expression of FIF in crest cells that would otherwise follow a different developmental pathway. 相似文献
3.
Jutta Begerow 《Biomarkers》1999,4(1):27-36
The aim of this study was to investigate to which extent noble-metal dental alloys contribute to the total platinum (Pt), palladium (Pd), and gold (Au) body burden of the general population. The urinary Pt, Pd, and Au excretion was determined in three non-occupationally exposed volunteers before and up to 3 months after insertion of a highgold dentalalloy. The in-vitro release of Pt, Pd, and Au from four different types of dental alloys into either artificial saliva or 1% lactic acid solution was additionally investigated. The Pt, Pd, and Au concentrations were determined by sector field inductively coupled plasma mass spectrometry (SF-ICP-MS). Before insertion of the high-gold dental alloy, the Pt excretion of the patients ranged between 1.0 and 7.4 ng l-1 (0.6-3.3 ng g-1 creatinine). In the immediate post-insertion phase the Pt excretion rose to 10.5-59.6 ng l-1 (14.5-33.2 ng g-1 creatinine). This is a mean increase by a factor of 12 compared with the average Pt excretion before insertion. Three months after insertion, the Pt excretion was still elevated by a factor of 7. Contrary to Pt, the Au and Pd excretion in urine was not significantly increased after insertion of this type of high-gold dental alloy. Our in-vitro investigations confirm the assumption that Pt, Pd, and Au are released from noble metal containing dental alloys by corrosion. Under the applied conditions, the release was in the lower ng cm-2 range. It can be concluded that the Pt release from dental alloys can predominantly contribute to the Pt exposure of non-occupationally exposed persons. It can exceed the exposure from all other environmental sources including the Pt release from automobile exhaust catalysts. 相似文献
4.
The Enterococcus faecalis conjugative plasmid pCF10 was used to introduce Tn925 into Acetobacterium woodii by filter mating. Tetracycline resistance was transferred at frequencies of about 10(-6) per donor, but no plasmid DNA was found in the transconjugants. DNA hybridization analyses of HindIII-digested chromosomal DNA demonstrated the insertion of Tn925 at a variety of locations, whereas wild type DNA showed no hybridization at all. The transconjugants were used as donor in mating experiments with tetracycline-sensitive Bacillus subtilis. Transfer of tetracycline resistance was observed at frequencies of 10(-8) per recipient. 相似文献
5.
6.
A transmembrane Na+ gradient was generated by Methanosarcina barkeri during methanogenesis. The intracellular Na+ concentration amounted to approximately one fifth of the extracellular one. A secondary Na+/H+ antiport system was shown to be responsible for Na+ extrusion. This system could be inhibited by amiloride. In the presence of amiloride the delta pH across the cytoplasmic membrane increased and a transmembrane Na+ gradient could neither be generated nor maintained. The possible role of Na+ in the oxidation of methanol to the level of formaldehyde is discussed. 相似文献
7.
ATP synthesis coupled to methane formation from methyl-CoM and H2 catalyzed by vesicles of the methanogenic bacterial strain G?1 总被引:3,自引:0,他引:3
Methanogenesis from methyl-CoM and H2, as catalyzed by inside-out vesicle preparations of the methanogenenic bacterium strain G?1, was associated with ATP synthesis. That this ATP synthesis proceeded via an uncoupler-sensitive transmembrane proton gradient was concluded from the following results: 1. Various inhibitors that affected methane formation (e.g. 2-bromomethanesulfonate) also prevented ATP synthesis. 2. The protonophore 3,5-di-tert-butyl-4-hydroxybenzylidenemalononitrile, in combination with the K+ ionophore valinomycin, inhibited ATP synthesis completely without affecting methanogenesis. 3. The ATP synthase inhibitor diethylstilbestrol inhibited ATP synthesis. 4. Addition of the detergent sulfobetaine inhibited both methane formation and ATP synthesis; the former but not the latter could be restored by adding titanium(III) citrate as electron donor. In addition it was shown that ATP synthesis could also be driven by transmembrane proton gradients artificially imposed on the vesicles. Furthermore net methanogenesis-dependent ATP formation was shown by measuring [32P]phosphate incorporation. 相似文献
8.
The distribution of the F420-reactive and F420-nonreactive hydrogenases from the methylotrophic Methanosarcina strain Gö1 indicated a membrane association of the F420-nonreactive enzyme. The membrane-bound F420-nonreactive hydrogenase was purified 42-fold to electrophoretic homogeneity with a yield of 26.7%. The enzyme had a specific activity of 359 mol H2 oxidized · min-1 · mg protein-1. The purification procedure involved dispersion of the membrane fraction with the detergent Chaps followed by anion exchange, hydrophobic and hydroxylapatite chromatography. The aerobically prepared enzyme had to be reactivated anaerobically. Maximal activity was observed at 80°C. The molecular mass as determined by native gel electrophoresis and gel filtration was 77000 and 79000, respectively. SDS gel electrophoresis revealed two polypeptides with molecular masses of 60000 and 40000 indicating a 1:1 stoichiometry. The purified enzyme contained 13.3 mol S2-, 15.1 mol Fe and 0.8 mol Ni/mol enzyme. Flavins were not detected. The amino acid sequence of the N-termini of the subunits showed a higher degree of homology to cubacterial uptake-hydrogenases than to F420-dependent hydrogenases from other methanogenic bacteria. The physiological function of the F420-nonreactive hydrogenase from Methanosarcina strain Gö1 is discussed.Abbreviations
transmembrane electrochemical gradient of H-
- CoM-SH
2-mercaptoethanesulfonate
- F420
(N-l-lactyl--l-glutamyl)-l-glutamic acid phospodiester of 7,8-didemethyl-8-hydroxy-5-deazariboflavin-5-phosphate
- F420H2
reduced F420
- HTP-SH
7-mercaptoheptanoylthreonine phosphate
-
Mb.
Methanobacterium
- PMSF
phenylmethyl-sulfonylfluoride
- Cl3AcOH
trichloroacetic acid 相似文献
9.
Summary The Saccharomyces cerevisiae KEX2 gene encodes the membrane-bound endoprotease yscF, which is responsible for the site-specific endoproteolytic cleavages at pairs of basic amino acid residues in the -factor precursor. In order to obtain soluble yscF activity, a mutant KEX2 gene lacking 600 bp coding for the C-terminal 200 amino acids was constructed. Expression of the truncated KEX2 gene in yeast led to the secretion of an active soluble yscF protein (yscFs). The soluble yscF protein is able to efficiently cleave heterologous protein precursors in-vitro, as demonstrated for -factor leader-hIGF1 and -factor leader-hirudin fusion proteins.
Offprint requests to: P. G. Seeboth 相似文献
10.
Acetylene inhibition technique underestimates in situ denitrification rates in intact cores of freshwater sediment 总被引:5,自引:0,他引:5
Abstract Denitrification in intact sediment cores was measured by the acetylene inhibition technique and compared with the nitrate flux between water and sediment. Less than half of the nitrate-N consumed by the sediment could be recovered as nitrous oxide-N. The low recovery rate of nitrous oxide from intact sediment cores indicated losses of nitrous oxide by diffusion down to nitrate-free sediment layers, where reduction of nitrous oxide may take place. In sediment slurries 100% of nitrate-N could be recovered as nitrous oxide-N as long as the nitrate concentration in the liquid phase was above 10 μM. Nitrous oxide added to nitrate-free sediment slurries was reduced regardless of whether acetylene was present or not. Therefore denitrification may be significantly underestimated by this method. 相似文献