Lymphokine regulation of human lymphocyte proliferation: Formation of resting G0 cells by removal of interteukin 2 in cultures of proliferating T lymphocytes

The question of whether lymphocytes which have once been activated and have completed one or several cell cycle(s) can return to the G₀ phase and stay ready for a new activation (G₀-G₁ transition), rather than simply die, was investigated. To do so interleukin 2 (IL-2) was removed from cultures of continuously proliferating human T lymphocytes and the formation of resting (G₀) cells was measured. Kinetic analyses in freshly prepared peripheral blood lymphocytes (PBL) revealed that the onset of detectable RNA synthesis and the appearance of structures binding the anti-Tac antibody occurred simultaneously. This allowed the expansion of the definition of G₀ T lymphocytes as cells having a low RNA (and DNA) content, and no Tac antigen. When cultured human T cells proliferating continuously by means of IL-2 were characterized in terms of their distribution in the cell cycle, 7 days after the initial PHA stimulation, it could be demonstrated that very few cells were in the G₀ phase, supporting the concept of direct S/G₂/M-G₁ transition. However, when IL-2 was removed from the cultures, the [³H]thymidine incorporation per 10⁴ cells and correspondingly the number of cells in the S/G₂/M and G₁ phases were reduced drastically and during the following 72-hr period, the number of G₀ cells increased markedly. Restimulation of such in vitro formed G₀ cells, under conditions permitting observation of their shift from the G₀ to G₀ phase, demonstrated that most cells could respond normally. Based on these observations, it was concluded that IL-2 not only ensures T-lymphocyte survival and proliferation, but IL-2 starvation induces many continuously proliferating T lymphocytes to stop cycling and to return to the G₀ phase of the cell cycle where they remain functional.     

Glycinebetaine content of halophytes: Improved analysis by liquid chromatography and interpretations of results

The glycinebetaine content of plants can be determined by simple isocratic high performance liquid chromatography. The method is applicable to extracts from a wide range of species and, in most cases, is suitably rapid and specific to be preferable to other methods of analysis. The chromatographic system employed permits accurate and sensitive ultraviolet detection, free of most interferences. Because the principle plant carbohydrates elute well before glycine betaine, preparative ion exchange procedures can be simplified. Twenty-seven species, mostly inland halophytes, were screened by these methods and 13 were found to be glycinebetaine accumulators. On a dry weight basis, the glycinebetaine content of Salicornia europaea L. actually declined with exposure to progressively higher levels of NaCl. When expressed as a proportion of plant organic matter, however, patterns were more typical (up to 7.7% at higher salt concentrations).     

A proton-deuterium exchange study of three types ofDesulfovibrio hydrogenases

Summary Hydrogenases are among the main enzymes involved in bacterial anaerobic corrosion of metals. The study of their mode of action is important for a full comprehension of this phenomenon. The three types ofDesulfovibrio hydrogenases [(Fe), (NiFe), (NiFeSe)] present different patterns in the pH dependence of their activity. The periplasmic enzyme fromDesulfovibrio salexigens and the cytoplasmic enzyme fromDesulfovibrio baculatus both have pH optima at 7.5 for H₂ uptake and 4.0 for H₂ evolution and H⁺–D₂ exchange reaction (measured by membrane-inlet mass-spectrometry). The H₂ to HD ratio at pH above 5.0 is higher than 1.0. The periplasmic hydrogenase fromD. gigas presents the same pH optimum (8.0) for the H⁺–D₂ exchange as for H₂ consumption. In contrast, the enzyme fromD. vulgaris has the highest activity in H₂ production and in the exchange at pH 5.0. Both hydrogenases have a H₂-to-HD ratio below 1.0.     

The relationship between hydrogen metabolism,sulfate reduction and nitrogen fixation in sulfate reducers

Summary Hydrogenase and nitrogenase activities of sulfate-reducing bacteria allow their adaptation to different nutritional habits even under adverse conditions. These exceptional capabilities of adaptation are important factors in the understanding of their predominant role in problems related to anaerobic metal corrosion. Although the D₂–H⁺ exchange reaction indicated thatDesulfovibrio desulfuricans strain Berre-Sol andDesulfovibrio gigas hydrogenases were reversible, the predominant activity in vivo was hydrogen uptake. Hydrogen production was restricted to some particular conditions such as sulfate or nitrogen starvation. Under diazotrophic conditions, a transient hydrogen evolution was followed by uptake when dinitrogen was effectively fixed. In contrast, hydrogen evolution proceeded when acetylene was substituted as the nitrogenase substrate. Hydrogen can thus serve as an electron donor in sulfate reduction and nitrogen metabolism.     

Nucleic acid hybridisation with a probe specific for 3 aminoglycoside acetyltransferase type IV: A survey of resistance to apramycin and gentamicin in animal strains of Escherichia coli

Abstract Resistance to apramycin due to production of a 3-aminoglycoside acetyltransferase type IV (AAC(3)IV) has recently been detected among Gram-negative bacteria isolated in France from bovine clinical samples. 24 apramycin-resistant Escherichia coli strains isolated over the country, and epidemiologically unrelated, were studied by colony hybridization using an intragenic probe specific for AAC(3)IV. The results obtained indicated that the structural gene for the acetyltransferase was present in all the isolates tested and in the corresponding apramycin-resistant transconjugants. This observation demonstrates that resistance to apramycin by acetylation of the antibiotic has spread very rapidly in bovine Gram-negative bacteria.     

Alpha-melanotropin in the frog brain: regional distribution, quantification and subcellular distribution

The distribution of alpha-MSH containing neurons was studied by immunofluorescence in the brain of the frog Rana ridibunda. Most immunoreactive cell bodies were found in the ventral hypothalamic area. A rich network of fluorescent fibers was observed in the ventral infundibular region, coursing towards the preoptic area and the ventral telencephalon. Some fibers, directed backwards, project into median eminence. By means of a specific radioimmunoassay, the concentrations of alpha-MSH immunoreactive material has been determined in 10 different regions of the brain. The highest concentrations were observed in the infundibular and the preoptic regions. Using the immunogold technique, electron microscopy showed that immunostaining was restricted to 70-100 nm dense core vesicles in positive cell bodies and fibers. These results suggest that, in addition to well known hormonal (melanotropic) activity, alpha-MSH could play the role of a neurotransmitter in the frog brain.     

Cold stress induces in situ phospholipid molecular species changes in cell surface membranes

The structural organization of Tetrahymena pyriformis is such that its cilia are remote from the main centers of lipid metabolism. As a result, the ciliary membrane lipid composition of cells exposed to low-temperature stress is initially unaffected by the significant metabolic changes induced in microsomal membranes. Nevertheless, changes in the ciliary membrane lipid composition can be detected during the first 4 h of cold exposure. A combination of in vivo and in vitro experiments has provided strong evidence for a substantial retailoring of ciliary phospholipid molecular species in situ in the absence of any importation of lipids from the cell interior or change in overall ciliary fatty acid composition. The mechanism responsible for the ciliary lipid changes is independent of the one(s) triggering internal acclimation responses. Our observations establish for the first time that chilling stress can simultaneously induce separate and distinctive lipid modification responses in different parts of a cell. This finding could be important in identifying the molecular ‘sensor’ capable of actuating stress-induced lipid changes.     

Structural investigation of the capsular polysaccharide produced by a novel Klebsiella serotype (SK1). Location of O-acetyl substituents using NMR and MS techniques

The capsular polysaccharide of Klebsiella SK1 was investigated by methylation analysis, Smith degradation, and ¹H NMR spectroscopy. The oligosaccharides (P1 and P2) obtained by bacteriophage ΦSK1 degradation of the polymer were studied by methylation analysis, and 1D- and 2D-NMR spectroscopy. The resulting data showed that the patent repeating unit is a branched pentasaccharide having a structure identical to the revised structure recently proposed for Klebsiella serotype K8 capsular polysaccharide.

The 2D-NMR data showed that one third of the glucuronic acid residues in the SK1 polymer are acetylated at O-2, O-3, or O-4. FABMS studies confirmed the presence of monoacetylated glucuronic acid residues. Thus, the relationship between the Klebsiella K8 and SK1 polymers is akin to that found for Klebsiella polysaccharides K30 and K33, which have been typed as serologically distinct yet their structures differ only in the degree of acetylation.     

Photochemical changes of fluorescent probes in membranes and their effect on the observed fluorescence anisotropy values

The fluorescence intensity of diphenylhexatriene (DPH) and of trimethylammonium-diphenylhexatriene (TMA-DPH) is measured when these probes are embedded in vesicles of dipalmitoyl- and dioleoylphosphatidylcholine (DPPC and DOPC), in mixtures of these vesicles as well as in vesicles of the mixed phospholipids, in trout intestinal brush border membranes and in mitoplasts of rat liver cells. The intensity in DOPC vesicles is found to be significantly higher than in DPPC vesicles. When these systems are irradiated with strong ultraviolet light radiation, a decrease in the fluorescence intensity is observed; this effect is much stronger in DOPC than in DPPC vesicles. The fluorescence anisotropy values in the mixture of vesicles as well as in the membranes show an initial increase with irradiation which is followed by a significant decrease. A transfer of DPH molecules between DPPC and DOPC vesicles is observed. For TMA-DPH this transfer takes place only from DPPC to DOPC vesicles, but not vice-versa. These results are related to intensity and anisotropy measurements of these probes in cell cultures.