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31.
Purified human milk beta-N-acetylglucosaminide beta 1, 4 galactosyltransferase (EC 2.4.1.38) was used to galactosylate N-acetylglucosamine (GlcNAc) residues present in ultra-thin sections of Lowicryl K4M-embedded rat and pig liver. Both endogenous galactose and galactosylated transferase products could be revealed by Ricinus communis lectin I-gold complexes (RcL I-g15). Without galactosyltransferase (GT) treatment, labeling for galactose (gal) was limited to the trans region of rat and pig hepatocyte Golgi apparatus. After exposure to GT, additional labeling was found over cis Golgi apparatus cisternae. RcL I-g15 labeling was sensitive to a purified preparation of endoglucosaminidase F/peptide N-glycosidase F (at pH 9). This indicates that endogenous gal and gal transferred by GT to terminal GlcNAc residues are present N-linked oligosaccharides. The RcL I-g15 labeling produced by GT was insensitive to extensive washing with solutions containing either EDTA and urea or SDS and 2-mercaptoethanol or 0.1 M GlcNAc. Substrate inhibition studies showed that 50 mM GlcNAc specifically inhibited the additional RcL I-g15 labeling produced by GT. The use of purified glycosyltransferases therefore appears to allow specific detection of oligosaccharide substrates and their high resolution localization in thin sections by electron microscopy.  相似文献   
32.
Barbiturate actions on excitatory synaptic responses in CA 1 and dentate regions of hippocampal slices were studied to determine whether different effects occur on anatomically distinct synaptic pathways. Pentobarbital facilitated transmission between stratum radiatum inputs and CA 1 neurons at low concentrations (0.02-0.08 mM) and produced postsynaptic depression at higher concentrations. Only depression was observed for stratum oriens inputs to CA 1 and perforant path inputs to dentate granulae neurons. The (+) isomer of pentobarbital was approximately four times more potent than the (-) isomer of racemic mixture. Phenobarbital (0.04-0.12 mM) produced only depression of synaptic responses in CA 1 and dentate pathways. Comparison of effect on field excitatory postsynaptic potentials and population spike responses indicated that the barbiturates act at selective and pathway-specific sites. The results provide further evidence for specific cellular and membrane recognition sites for barbiturate action.  相似文献   
33.
Polypeptide components and carbohydrate linkage types of F11 antigen and G4 antigen, two chick cell-surface glycoproteins implicated in neurite fasciculation and elongation [Rathjen, F.G., Wolff, J.M., Bonhoeffer, F. and Rutishauser, U. (1987) J. Cell Biol. 104, 343-353], have been studied in comparison to mouse L1 antigen. Tryptic fingerprint analysis does not reveal any relation of the 130-kDa components of G4 or F11 antigens to each other or to neural cell-adhesion molecules. The 180/190-kDa component of G4 antigen comprises parts of the 130-kDa and 80/65-kDa components and shares a sequence corresponding to the amino terminus of the G4 130-kDa component as shown serologically with anti-peptide sera. This closely parallels the relationship found for mouse L1 antigen components. In contrast, the F11 170-kDa component is different from the F11 130-kDa component, as shown serologically and by fingerprint analysis. A combination of chemical and enzymatic deglycosylation methods reveals that while O-glycosylation cannot be detected F11 130-kDa, G4 130-kDa and L1 140-kDa components contain N-linked carbohydrates. Endoglycosidase H treatment shows that the oligosaccharides present in the G4 130-kDa component and mouse L1 are mostly of the complex type, while the F11 130-kDa component consists of two populations, one containing mainly complex-type carbohydrates and a second containing high-mannose/hybrid-type carbohydrates.  相似文献   
34.
The protein A-gold technique is amongst the most useful labeling techniques available for light and electron microscopic immunolabeling. Some electron microscopic studies, however, have suggested that protein A-gold, and other protein-gold complexes as well, may bind non-specifically to certain tissue structures, particularly in skin, creating a specious pattern of labeling. We utilized the protein A-gold technique with antiserum to both involucrin and keratin under a variety of conditions to document the specificity of labeling. When the standard conditions were followed, the protein A-gold technique produces highly specific results. These conditions include: 1. the blocking of unreacted aldehyde groups by amination; 2. the blocking of non-specific binding sites on tissue sections by preincubation with inert proteins; and 3. the use of proper concentration of the protein A-gold complex. However, non-specific labeling could be produced if the three components of the standard protocol were omitted. In particular, the use of too concentrated protein A-gold lead to non-specific labeling. We report here also updated working protocols for antigen detection with protein A-gold on semithin Lowicryl K4M and paraffin sections which provide optimal staining results.  相似文献   
35.
Modified blastocyst injection techniques were used to inject immunosurgically isolated sheep x goat hybrid inner cell masses (ICM) into ovine blastocysts, with subsequent transfer of composite embryos to ovine recipients. Hybrid embryos were collected from does artificially inseminated with Barbados ram semen. A total of 13 live and 2 aborted offspring resulted from the 34 composite embryos transferred to recipient ewes (38% embryo survival). Of the 15 offspring, 4 exhibited phenotypic hybridism and 2 (13%) of these were determined to be hybrid mean value of -sheep chimeras by karyotype, serum protein and isoenzyme analyses, and fiber identification. Each of the 4 was produced by an injection procedure that involved damage of the ovine host ICM. One additional offspring was unusual in appearance, but the presence of hybrid cells was not proven. Similarly, caprine ICM were immunosurgically isolated and injected into ovine blastocysts that were then transferred to ovine recipients. Of the 13 composite embryos transferred, 12 offspring were produced (92% embryo survival). Eleven were overt goat mean value of -sheep chimeras and, of these, 7 were also blood chimeras. The hybrid ICM was shown to be capable of contributing to normal embryonic and fetal development after injection into an ovine blastocyst but may be less likely to be incorporated with the ovine host ICM than is the caprine ICM.  相似文献   
36.
Lipopolysaccharides of different wild-type and mutant gram-negative bacteria, as well as synthetic and bacterial free lipid A, were studied for their ability to activate arachidonic acid metabolism in mouse peritoneal macrophages in vitro. It was found that lipopolysaccharides of deep-rough mutants of Salmonella minnesota and Escherichia coli (Re to Rc chemotypes) stimulated macrophages to release significant amounts of leukotriene C4 (LTC4) and prostaglandin E2 (PGE2). Lipopolysaccharides of wild-type strains (S. abortus equi, S. friedenau) only induced PGE2 and not LTC4 formation. Unexpectedly, free bacterial and synthetic E. coli lipid A were only weak inducers of LTC4 and PGE2 production. Deacylated Re-mutant lipopolysaccharide preparations were inactive. However, co-incubation of macrophages with both deacylated lipopolysaccharide and lipid A lead to the release of significant amounts of LTC4 and PGE2, similar to those obtained with Re-mutant lipopolysaccharide. The significance of the lipid A portion of lipopolysaccharide for the induction of LTC4 was indicated by demonstrating that peritoneal macrophages of endotoxin-low-responder mice or of mice rendered tolerant to endotoxin did not respond with the release of arachidonic acid metabolites on stimulation with Re-mutant lipopolysaccharide and that polymyxin B prevented the Re-lipopolysaccharide-induced LTC4 and PGE2 release. Physical measurements showed that the phase-transition temperatures of both free lipid A and S-form lipopolysaccharide were above 37 degrees C while those of R-mutant lipopolysaccharides were significantly lower (30-35 degrees C). Thus, with the materials investigated, an inverse relationship between the phase-transition temperature and the capacity to elicit LTC4 production was revealed.  相似文献   
37.
Bacterial DNA ligases use NAD as an energy source. In this study we addressed two questions about these enzymes. First, what is the physiological consequence of completely removing the NAD-dependent enzyme and replacing it with an ATP-dependent DNA ligase? We constructed Salmonella typhimurium strains in which the endogenous NAD-dependent DNA ligase activity was inactivated by an insertion mutation and the ATP-dependent enzyme from bacteriophage T4 was provided by a cloned phage gene. Such strains were physiologically indistinguishable from the wild type, even under conditions of UV irradiation or treatment with alkylating agents. These results suggest that specific functional interactions between DNA ligase and other replication and repair enzymes may be unimportant under the conditions tested. Second, the importance of DNA ligation as the initiating event of the bacterial pyridine nucleotide cycle was critically assessed in these mutant strains. Surprisingly, our results indicate that DNA ligation makes a minimal contribution to the pyridine nucleotide cycle; the Salmonella strains with only an ATP-dependent ligase had the same NAD turnover rates as the wild-type strain with an NAD-dependent ligase. However, we found that NAD turnover was significantly decreased under anaerobic conditions. We suggest that most intracellular pyridine nucleotide breakdown occurs in a process that protects the cell against oxygen damage but involves a biochemical mechanism other than DNA ligation.  相似文献   
38.
Previous analysis of Rendille household herd composition revealed a transition from camel to cattle ownership for sedentary impoverished Rendille pastoralists of northern Kenya. In an attempt to delineate determinants of livestock holdings, logistic regression analysis of 112 household herds from the Rendille settlement of Korr, Marsabit District, Kenya was undertaken. Results indicated that household wealth, measured in present livestock holdings, past drought losses, and livestock sales, formed better predictors of cattle ownership than did household characteristics pertaining to labor supply, wage earners, age-set membership, and birth order of household head. These results are discussed in light of pastoral strategies designed to minimize risk.  相似文献   
39.
This paper examines the effects of the 1984 drought upon household wealth differences in a community of Ariaal pastoralists of northern Kenya. The database consists of 1985 post-drought livestock counts and informants' statements of species-specific drought loss, compared to 1976 livestock counts on the same 38 households. The analysis confirms the hypothesis that the drought resulted in increased household wealth inequalities. It is suggested that the combination of differential herd growth, differential participation in the cash market, and differential loss to the drought has contributed to a polarization within Ariaal of rich and poor, resulting in rural proletarianization and urban migration.  相似文献   
40.
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