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11.
A number of different membrane associated isoforms of the neural cell adhesion molecule (N-CAM) have previously been identified. Here the structure of a novel secreted isoform of N-CAM is established by analysis of a cDNA corresponding to an N-CAM mRNA from human skeletal muscle. The mRNA incorporates a novel sequence block into the extracellular domain, which introduces an in-frame stop codon and thus prematurely terminates the coding sequence, generating a truncated N-CAM polypeptide. Analysis of genomic clones indicates that the inserted sequence is present as a discrete exon within the human N-CAM gene, and Northern analysis shows it to be associated specifically with a 5.2 kb mRNA species from skeletal muscle and brain. Stable transfectants expressing the secreted isoform accumulate it in the cytoplasm and release it to the culture medium. In contrast, cells transfected with cDNA encoding lipid-tailed N-CAM express it predominantly at the cell surface. The existence of a secreted isoform may further expand the spectrum of N-CAM function beyond its known involvement in intercellular adhesion to extracellular matrix interactions. 相似文献
12.
Daily activity levels of black-backed jackals Canis mesomelus were determined in southern Africa through direct observation and radio-tracking. Jackals have a bigeminus activity pattern that is closely paralleled by the activity levels of some of their most important prey. Although differences due to sex, age, study area and season of year were found, this activity pattern was most markedly influenced by light conditions during both the crepuscular and the nocturnal periods. 相似文献
13.
The activity levels of enzymes of aromatic amino acid biosynthesis respond to changing physiological states of growth, as illustrated by results obtained from suspension-cultured cells of Nicotiana silvestris Speg. et Comes line ANS 1 (2N=24). The experimental system provides a foundation for interpretations about overall regulation of enzyme levels in relationship to growth physiology. Levels of activity for shikimate dehydrogenase (EC 1.1.1.25), prephenate aminotransferase and arogenate dehydrogenase were followed throughout a growth cycle obtained by a conventional subculture protocol. Enzyme date were also obtained from cell cultures maintained in continuous exponential growth for greater than 10 generations (EE cells). Both shikimate dehydrogenase and prephenate aminotransferase exhibited elevated stationary-phase levels of enzyme, much of which was carried over into a subsequent subculture. At least 4 generations of exponential growth were required before diminution of the latter two enzymes to the levels characteristic of truly exponential-phase growth (EE cells) occurred. This is reminiscent of the overall behavior of 3-deoxy-D- arabino -heptulosonate 7-phosphate (DAHP) synthase (EC 4.1.2.15), specifically attributed to the properties of the cytosolic isozyme species (DAHP synthase-Co). Elevation of arogenate dehydrogenase also occurred in stationary-phase cells, but diminished rapidly during lag phase to reach the level characteristic of EE cells. 相似文献
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Gianluigi Discalzi Francesco Furno Luigi Gagliardi Mario Ambroso Jacqueline Mavro 《Aerobiologia》1992,8(1):62-68
Summary The purpose of this study is to verify and assess, in working conditions, the respiratory exposure to PPD of hairdressing parlour personnel. Several air samples collected in a hairdressing parlour during the time required for 8 applications of dyeing products containing PPD 2.52% have been analyzed. Tests are also carried out by extracting air immediately above the bowls containing the dyeing products, both at room temperature and at 37°C. PPD was assessed by means of HPLC. Only air sampled directly on bowls at 37°C has shown a level of 1 g, corresponding to an environmental release of PPD equivalent to 8 applications of dyeing products. On the basis of these experimental data, the PPD concentration in the air according to the parlour volume and to the supposed air exchanges has been calculated. Our results show a substantial insignificance of the concentration of PPD released in the environmental air during normal operations of hair dyeing: authors are of the opinion that hairdressers can't be truly considered as a PPD-asthmatic risk category like other workers exposed to PPD dust dispersed in the air of their working environment. 相似文献
18.
The HLA class I sequences included in this compilation are taken from publications listed in the accompanying paper, Nomenclature for factors of the HLA system, 1990 (Bodmer et al. 1991) and Nomeclature for factors of the HLA system, 1989 (Bodmer et al. 1990). Where discrepancies have arisen between reported sequences the original authors have been contavted where possible, and necessary amendments to published sequences have been incorporated into this alignment. Future sequencing may identify errors in this list and we would welcome any evidence that helps to maintain the accuracy of this compilation. In the sequence alignments identify between residues is indicated by a hyphen (-). Unavailable sequence is indicated by a period (.). Gaps in the sequence are inserted to maintain the alignment between different alleles showing variation in amino acid number. 相似文献
19.
Liquefaction of dry and freshPalmaria palmata by food grade enzyme preparations and a purified endo--1,4-D-xylanase was studied.The endo--1,4-D-xylanase (EC 3.2.1.8) was purified to homogeneity from a commercial food grade enzyme prepared fromAspergillus niger. It has a molecular weight of 22 500, a pI of 3.5, is inactive toward corn arabinoxylan,p-nitrophenyl--D-xylose, carboxymethyl cellulose but shows a weak activity toward microcrystalline cellulose. It hydrolyzes oat and dulse xylan equally well in seawater and deionized water essentially into xylose and xylobiose. It is stable between pH 5.5 to 9.0 and 0 to 30 °C and its activity is optimal at pH 4.5–5.5 and 40–60 °C. It has a Km of 2.2 and 2.8 mg ml-1 and Vmax of 3600 and 3900 nkat mg-1 of protein on oat and dulse xylan, respectively.Acetate buffer, deionized water and seawater alone extracted 62.6 to 64.5 % of the dry weight of dry dulse, but the use of commercial food grade enzyme preparations or the purified xylanase improved liquefaction to 81.2–87.1 %. Xylose and galactose were the only sugars present in the soluble extracts. Deionized and seawater extracted 58.8–52.7 and 39.1–42.2% of the dry weight of the fresh algae collected in fall and summer, respectively. Only galactose was found in the seawater extract, while some xylose with galactose were measured in the deionized water extract of the fresh autumn algal sample. Purified and crude xylanase improved liquefaction of fresh algae to 79.8–81.4 and 71.9–77.9% of the fresh dry weight (fall and summer, respectively) in deionized and seawater, respectively, and increased the xylose content of the soluble fractions. Polysaccharides in the soluble residues were composed of 1,3/1,4-linked xylose, 1-linked galactose (floridoside) and 1,4-linked glucose (cellulose) and contained essentially 1,4-linked xylose and 1,4-linked glucose in insoluble fractions obtained after enzymatic treatment.The use of xylanase-containing food grade enzyme preparations improves liquefaction ofPalmaria palmata, particularly from fresh alga. This study indicates that processing such as drying may modify markedly the solubility ofP. palmata cell wall polysaccharides, which would imply the existence of some organization and/or other components in the fresh cell wall that lower xylan solubility in seawater. 相似文献
20.
R. Michael Snider Dennis A. Pereira Kelly P. Longo Ralph E. Davidson Frederic J. Vinick Kirsti Laitinen Ece Genc-Sehitoglu Jacqueline N. Crawley 《Bioorganic & medicinal chemistry letters》1992,2(12):1535-1540
UK-73,093 was identified in a screening program as a compound able to displace [3H]-neurotensin from its bovine brain receptor. We describe the discovery of this compound, species differences in receptor affinity and its characterization as a functional neurotensin antogonist in vitro and in vivo. 相似文献