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The risk of malignancy in large congenital nevi 总被引:4,自引:0,他引:4
E N Kaplan 《Plastic and reconstructive surgery》1974,53(4):421-428
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Regulatory volume decrease in alveolar macrophages: cation loss is not correlated with changes in membrane recycling 总被引:2,自引:0,他引:2
Alveolar macrophages regain their normal volume after swelling in hypo-osmotic solutions. This process, termed regulatory volume decrease (RVD), is initiated 3-5 minutes after exposure of cells to hypo-osmotic solutions, and by 30 min, near-normal volumes are attained. Volume decrease does not occur at 0 degrees C or in solutions in which Na+ has been replaced by K+, or Cl- by the impermeant anion gluconate. These results, as well as direct measurement of intracellular cations, indicate that decreases in cell volume result primarily from the loss of K+ and Cl- and are similar to RVD in lymphocytes. Kinetic analysis of cation loss, both by directly measuring changes in intracellular cation content and by assaying rubidium efflux, showed that cation loss occurred immediately upon media dilution. The rate of cation loss fit first-order kinetics and preceded both the initiation of volume decrease and the maximum increase in surface receptor number. These results suggest that the cation transporters responsible for RVD are located at the cell surface and that regulation of activity is not dependent on alterations in membrane movement. 相似文献
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The first seven amino acids encoded by the v-src oncogene act as a myristylation signal: lysine 7 is a critical determinant. 总被引:44,自引:14,他引:30
The transforming protein of Rous sarcoma virus, pp60v-src, is covalently coupled to myristic acid by an amide linkage to glycine 2. Myristylation promotes the association of pp60v-src with cellular membranes, and this subcellular location is essential for transforming activity. The findings presented here, in conjunction with the previous reports of others, imply that the seventh amino acid encoded by v-src might be important in the myristylation reaction. Replacement of lysine 7 by asparagine greatly reduced the myristylation, membrane association, and transforming activity of pp60v-src. In contrast, substitution of arginine at residue 7 had no effect on any of these properties of pp60v-src. Addition of amino acids 1 to 7 encoded by v-src was sufficient to cause myristylation of a src-pyruvate kinase fusion protein. We conclude that the recognition sequence for myristylation of pp60v-src comprises amino acids 1 to 7 and that lysine 7 is a critical component of this sequence. 相似文献
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Light-dependent regulation of the synthesis of soluble and intracytoplasmic membrane proteins of Rhodopseudomonas sphaeroides. 总被引:15,自引:13,他引:2 下载免费PDF全文
Cells of Rhodopseudomonas sphaeroides grown under saturating light conditions (30 W/m2) and then shifted to low light intensity (3 W/m2) required 2.5 h to adapt to the new lower light conditions. After the shift, cell growth, whole cell protein accumulation, and bacteriochlorophyll accumulation ceased immediately. Approximately midway into the adaptation period, bacteriochlorophyll synthesis commenced at a new, higher rate, which continued through the beginning of the low-light growth period until new steady-state levels were reached. Immediately after the downshift, the rate of cellular protein synthesis declined to 22% of its preshift rate. Pulse-labeling of protein throughout the adaptation period and comparison with a steady-state prelabel culture revealed that synthesis of two of the three light-harvesting proteins, as well as two additional high-molecular-weight photosynthetic membrane proteins, was derepressed three- to fivefold compared with bulk cellular protein. Finally, the synthesis of at least three soluble proteins showed light-dependent regulation after the light downshift. These results are discussed in terms of the light-dependent regulation of synthesis of the photosynthetic membrane macromolecular components and the division of protein synthesis between the photosynthetic membranes and the soluble cell phase. 相似文献
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Partial characterization and purification of the glycosylation site recognition component of oligosaccharyltransferase 总被引:3,自引:0,他引:3
Oligosaccharyltransferase, the enzyme catalyzing the co-translational transfer of oligosaccharide from dolichyl-PP-GlcNAc2Man9Glc3 to -Asn-X-Ser/Thr- sequences in nascent polypeptide chains, was studied in hen oviduct microsomes using the active site-directed photoaffinity probe 125I-labeled N alpha-3-(4-hydroxyphenylpropionyl)-Asn-Lys(N epsilon-p-azidobenzoyl)-Thr-NH2. Several lines of evidence established that the tripeptide probe interacted with a 57-kDa protein of the endoplasmic reticulum that was subsequently glycosylated and converted to a 60-kDa form. The 57-kDa protein, isolated by two-dimensional gel electrophoresis, was used as immunogen to prepare polyclonal antisera. The specificity of the antibody was established on the basis of its ability to 1) recognize the 57-kDa protein by immunoblotting and 2) immunoprecipitate the photolabeled protein. The antibody also recognized photolabeled protein from different tissues and organisms. The 57-kDa protein isolated by immunoprecipitation retained its ability to interact with the photoaffinity probe but was inactive in catalyzing glycosylation of peptides. This result suggests that the 57-kDa protein is the component of oligosaccharyltransferase that recognizes the glycosylation site in polypeptides. These results are discussed in terms of possible models for the structure of oligosaccharyltransferase in the endoplasmic reticulum. 相似文献
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To see if a Vitamin B6 deficiency is responsible for seizure-proneness in the gerbil, , a diet supplemented with 0.5mg of pyridoxine per gram of Purina Lab Chow was fed to 8 experimental (E) mated pairs and their litters while 8 control (C) pairs and their litters were fed Purina Lab Chow which contains .004mg per gram of pyridoxine. All litters were tested for seizures every 2 weeks from 2 through 7 mos. of age once a month in a standard (SS) test cage and 2 weeks later in a clean home cage (CC) — and again at 1 yr in the SS cage. There were no differences on any of the measures between E and C litters. Significantly more seizures were elicited in the SS than in the CC tests, and the SS test became increasingly more effective with age. It was concluded that gerbil seizures were not due to a Vitamin B6 deficiency and that some age-related process might be a productive area for future investigation. 相似文献