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81.
82.
Methylation of (R,S)-DOPA with diazomethane gave the trimethyl derivative in which the phenolic hydroxy groups and the carboxy group were methylated. N-Methylated side products were also formed. N-Acylation of the racemic trimethyl derivative with (S)-α-methoxy-α-trifluoromethylphenylacetyl chloride gave two diastereomeric amides which were resolved by gas chromatography, the diastereomer derived from (S)-(−)-DOPA cluting first. The procedure was also applied to α-methyl-DOPA. 相似文献
83.
A study was undertaken to evaluate the interrelationship between the presence of seagrasses, Zostera marina and Halodule wrightii, and the physical and chemical properties of sediments in a coastal plain estuary near Beaufort, North Carolina. In sediments underlying a cover of seagrass, silt-clay, organic matter, exchangeable ammonium, ammonium dissolved in pore waters and total nitrogen were larger than in unvegetated profiles. The magnitude of the physical and chemical properties of sediments varied according to the location of the station in relation to the vegetation, as well as the continuity in the distribution of the seagrass. The largest pools of nitrogen, the finest sediment texture, and the greatest organic matter content were in sediments associated with the mid bed regions of seagrass meadows, intermediate at the edges of the bed and small isolated patches of grass, and least in unvegetated substrate.General conclusions from this study are: 1) once established, seagrasses appear capable of modifying the sediment texture as well as the organic matter and nitrogen content; 2) nitrogen accumulates beneath the vegetation suggesting that vegetated sediments are sinks; however, functional recycling mechanisms seem to be operating as suggested by the larger magnitude of remineralized nitrogen in the vegetated profiles; and 3) the establishment of seagrasses in this geographical region are not necessarily restricted by the sediment properties measured in this study. These data and conclusions are discussed in regard to an application of contemporary theories of ecosystem development to seagrass systems.Contribution Number 82-22-B 相似文献
84.
Joseph G. O'Mara 《Antonie van Leeuwenhoek》1979,45(2):161-164
The thesis of this communication is that the secret method of Leeuwenhoek was the augmentation of the magnification of his single glass lens by the refraction at the quasi-hemispherical surface of a column of liquid containing the microorganisms. The linear increase in magnification thus secured could be as much as three-fold, depending on the degree of curvature of the liquid surface, the diameter of the column of liquid, and the index of refraction of the medium. This increase is more than adequate to account for the magnifications necessary for observation of details beyond the resolution of his best glass lenses. The hypothesis also accounts for the second part of the secret method, the high density of microorganisms in a single field of view, by successive reconstitutions of the curved surface of the medium. 相似文献
85.
86.
Bernard Possidente Joseph P. Hegmann 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1980,139(2):121-125
Summary Circadian rhythms for food and water consumption were measured in five inbred strains of mice under a photoperiod of 16 h light and 8 h dark (16:8 LD), and under constant light (LL).Significant strain differences were observed which indicate that a common gene difference, or set of differences inMus musculus influences both the phase angle () associating the rhythms with the light-dark cycle, and the periods (LL) of circadian rhythms for food and water consumption. The biological clock mechanism influenced by this genetic variance is common to both food and water circadian rhythms, and differs among the five inbred strains. A positive genetic correlation was observed between the phase angle () and the period (LL) of each rhythm. This observation can be understood in terms of a functional relationship between phase and period proposed by Pittendrigh and Daan (1976b) for the entrainment of a circadian oscillator by a light-dark cycle in nocturnal rodents.These results suggest that circadian rhythms for food and water consumption in mice are regulated by a common physiological mechanism, and would respond to natural selection as a single circadian complex under common gene control. 相似文献
87.
David Stiller Robert F. Whitcomb Michael E. Coan Joseph G. Tully 《Current microbiology》1981,5(6):339-342
A spiroplasma isolate, was obtained from rabbit ticks (Haemaphysalis leporispalustris) taken from cottontail rabbits in Maryland by inoculation of tick suspensions into SP-4 medium. The isolate was indistinguishable from an experimental vertebrate pathogen (suckling mouse cataract agent spiroplasma) when tested with other plant and tick spiroplasmas in growth inhibition, deformation, and metabolism inhibition tests. The isolated organism had a pathogenic profile for suckling rats and embryonated chicken eggs that differed significantly from that of other suckling mouse cataract agent strains. This is the first report of a direct spiroplasma isolation from ticks in cell-free medium, and confirms the specific association of spiroplasmas of the suckling mouse cataract agent serogroup with rabbit ticks. 相似文献
88.
89.
William R. Tolbert Joseph Peder Richard C. Kimes 《In vitro cellular & developmental biology. Plant》1981,17(10):885-890
Summary A system has been developed for growth and maintenance of mammalian cells in suspension culture at high density. In principle,
the maintenance of constant levels of required nutrients coupled with the removal of toxic cell byproducts can support much
higher suspension cell densities than may be obtained in conventional spinners. The system consisted of 4- or 40-liter reaction
vessels equipped with a vertically supported rotating cylindrical filter. Agitation was provided by the magnetically driven,
rotating filter. Fresh medium was supplied at a rate of 10 to 20 ml/h per 109 cells and the expended medium free of cells was withdrawn through the rotating filter. Both pH and dissolved O2 and CO2 were monitored and regulated. Walker 256 carcinosarcoma cells have been grown in these reactors to densities 10-to 30-fold
greater than that obtained in Bellco spinners. In addition to high cell densities, the yield of cells per liter of medium
used was 2- to 3-fold that obtained in the conventional systems. Both 4-and 40-liter versions of this reactor have been operated
without the use of antibiotics. The 40-liter reactor also has been modified for chemostat operation. In a single run, for
example, the Walker cell density was maintained between 6 and 10×106 cells/ml with a total yield of 8.7×1011 cells from 360 liters of medium. 相似文献
90.
The effect of human peripheral lymph on cell growth in vitro 总被引:1,自引:0,他引:1