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181.
182.
183.
Anthony A. Ribeiro Robert P. Saltman Murray Goodman Manfred Mutter 《Biopolymers》1982,21(11):2225-2239
The use of 1H-nmr spectroscopy is demonstrated to be a useful analytical method to characterize the structure of synthetic peptides attached to soluble, macromolecular polyoxyethylene (POE) supports in the liquid-phase method (LPM) of peptide synthesis. We report an extensive 360-MHz 1H-nmr study of POE-bound homo-oligo-L -methionine peptides. A combination of high field and selective saturation or Redfield pulse methods allows resolution of individual backbone NH and α-CH resonances of dilute peptides in the presence of strong resonances from macromolecular POE and/or protonated solvents. The nmr spectra for the POE-bound peptides in CDCl3 are qualitatively similar to those of the low-molecular-weight Boc-L -Metn-OMe peptide esters. This corroborates other observations that POE has little effect on peptide stucture. The backbone α-CH region of peptides is overlapped by signals from the terminal oxyethylene group of POE, but the peptide side-chain and low-field backbone NH resonances are well resolved. In trifluoroethanol the Boc-(L -Met)n-NH-POE heptamer and octamer adopt the right-handed α-helical structure, and the present nmr studies provide evidence for two strong intramolecular hydrogen bonds to stabilize the helices. In water, the N-deblocked derivatives, (L -Met)n-NH-POE oligomers adopt β-sheet structure and manifest well-resolved nonequivalent NH resonances with 6–7 Hz 3JNH-CH coupling constants. 相似文献
184.
Isao Matsui Masaharu Kamei Shuzo Otani Seiji Morisawa Anthony E. Pegg 《Biochemical and biophysical research communications》1982,106(4):1155-1160
Spermidine acetylase activity was detected in extracts prepared from and there was a marked increase in activity over the early period of growth. This increase reached a maximum 3 h after inoculation and was followed by an increase in ornithine decarboxylase activity. The acetylase was also able to use spermine as a substrate, but not putrescine. With spermidine and acetyl-CoA as substrate, the product formed was exclusively N1-acetyl-spermidine. This is the first evidence for the occurrence in bacteria of spermidine-N1-acetyltransferase, an enzyme which has previously been described in mammalian cells. These results suggest that acetylation of spermidine may be involved in the growth of and in the regulation of its polyamine content. 相似文献
185.
Using UDP-d-galactose : 2-acetamido-2-deoxy-d-glucose 4-β-d-galactosyltransferase (EC 2.4.1.22), several methyl β-lactosides have been prepared with 2H- and/or 13C-enrichment at specific sites to facilitate study by 13C (75 MHz) and 1H (600 MHz) n.m.r. spectroscopy. 13C-Chemical shift assignments were verified and the 1H-spectrum of β-lactoside was fully assigned. Sites of enrichment were selected to permit all of the potential three-bond C-C and C-H couplings through the glycosidic bond to be obtained. Replacement of H-3 of the d-glucose residue of methyl β-lactoside with 2H allowed resolution of C-1–H-4′ coupling in the 600-MHz 1H-spectrum. Single or multiple 13C-enrichment at C-1, C-2, C-3, C-1′, C-3′, and/or C-4′ in the disaccharide allowed observation of intra- and inter-residue couplings. 13C-Spin-lattice relaxation-times (T1) are interpreted in terms of molecular motion in solution. The data suggest that methyl β-lactoside has an extended conformation with little rotation about the glycosidic bond. Inter-residue couplings are best explained by tortion angles of φ ~ 40° and ψ ~ 15°, indicating that the conformations of β-lactoside in solution and in the crystal are similar. 相似文献
186.
Edward L. Schwartz Anthony F. Hadfield Alfred E. Brown Alan C. Sartorelli 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1983,762(4):489-497
Two analogs of N-acetylmannosamine, (Ac4-NAcMan) and the 2-trifluoroacetamido derivative (Ac4F3-NAcMan), were synthesized as potential inhibitors of the formation of sialic acid-containing glycoconjugates and were examined for their ability to modify the incorporation of into cellular glycoconjugates of Friend murine erythroleukemia cells. Ac4F3-NAcMan and Ac4-NAcMan inhibited cellular replication in suspension culture at concentrations of 0.02 and 0.08 mM, respectively. The cytotoxicity of Ac4-NAcMan was relatively reversible, whereas that produced by Ac4F3-NAcMan was not, as judged by measurement of the cloning efficiencies of cells exposed to these agents. The analogs inhibited incorporation of into ethanol-soluble and -insoluble materials. Separation of ethanol-soluble metabolites by HPLC demonstrated that Ac4F3-NAcMan caused accumulation of radioactivity from in CMP-N-acetylneuraminic acid (CMP-NeuNAc) equal to the decrease in macromolecular-bound 3H caused by this agent. In contrast, similar exposure to Ac4-NAcMan produced a large increase in the amount of radioactivity in ethanol-soluble N-acetylneuraminic acid while decreasing the amount of label from in cellular CMP-NeuNAc, suggesting that the analogs differ in their biochemical sites of action. Treatment of cells with either analog increased the amount of neuraminidase-hydrolyzable sialic acid-like material on the cell surface; this appeared to be due to the incorporation of the analogs into cellular glycoconjugates, since incubation of cells with 3H-labeled analogs resulted in the appearance of radioactivity in cellular ethanol-insoluble and neuraminidase-hydrolyzable material. Incubation of cells with Ac4-NAcMan labeled with 14C in the 4-O-acetyl group further demonstrated that incorporation occurred with approx. 50% retention of this substituent. Thus, both the amount and the nature of the surface sialic acid constituents of treated cells were altered, suggesting that these or similar analogs could potentially be used to modify cellular membrane function. 相似文献
187.
Genetic and developmental evidence for a repressed genital primordium in Drosophila melanogaster 总被引:5,自引:0,他引:5
Lee Engstrom Joan H. Caulton Eileen M. Underwood Anthony P. Mahowald 《Developmental biology》1982,94(1):163-175
Agametic, a maternal-effect mutation, causes the absence of germ cells in approximately 40% of the gonads of flies derived from homozygous females. The nature of the deficiency in the eggs produced by these flies was examined. Ultrastructural abnormalities were seen in the polar granules of some eggs shortly after fertilization. Although a normal number of pole cells form, some are abnormal with degenerating polar granules and nuclear bodies and they contain myeloid bodies. The pole cells reach the gonads and at 14 hr of development all the gonads contain germ cells. However, in 40% of the gonads the germ cells become necrotic and disappear. Thus, the source of agametic gonads in the adult is embryonic death of pole cells in some gonads. To test whether this gonadal death is an autonomous deficiency of the mutant pole cells, mosaic pole cell populations were produced by reciprocal pole cell transplantation. In both types of transplants, the mutant pole cells died autonomously. In eight instances gonads containing only donor pole cells were obtained. Since mutant pole cells die when wild-type pole cells normally begin dividing, we suggest that the lesion affects the ability of these mutant pole cells to reenter the cell cycle. 相似文献
188.
Transformation and allelic replacement in Francisella spp. 总被引:1,自引:0,他引:1
L S Anthony M Z Gu S C Cowley W W Leung F E Nano 《Journal of general microbiology》1991,137(12):2697-2703
We describe methods for transposon mutagenesis and allelic replacement in the facultative intracellular pathogen Francisella. Recombinant clones were constructed by insertion of partially cut F. tularensis or F. novicida DNA into pUC19 and then mutagenized with a mini-Tn10-Km transposon. F. novicida could be transformed with these plasmids either by a chemical transformation method or by electroporation, whereas F. tularensis could be transformed only by electroporation. Transformation of F. tularensis by electroporation was enhanced in the absence of the capsule. Southern blot analysis showed that the KmR marker was rescued either by integration of the plasmid into the Francisella chromosome or by allelic replacement. Allelic replacement was found to be the mechanism underlying a site-specific mutation affecting FopA, an outer-membrane protein of Francisella. F. novicida could also be transformed with chromosomal DNA carrying the KmR marker and the transformation frequency obtained using chromosomal DNA was generally greater than that obtained using plasmid DNA. F. novicida was also transformed by an IncQ plasmid containing an F. novicida DNA insert, which replicated autonomously in this host. 相似文献
189.
Thomas A. Edsall Bruce A. Manny Donald W. Schloesser Susan J. Nichols Anthony M. Frank 《Hydrobiologia》1991,219(1):353-361
In April through October 1986, we sampled sediments and populations of nymphs of the burrowing mayfly, Hexagenia limbata (Serville), at 11 locations throughout the connecting channels of the upper Great Lakes, to determine if sediment contaminants adversely affected nymph production. Production over this period was high (980 to 9231 mg dry wt m-2) at the five locations where measured sediment levels of oil, cyanide, and six metals were below the threshold criteria of the U.S. Environmental Protection Agency and the Ontario Ministry of Environment for contaminated or polluted sediments, and also where the criterion for visible oil given in the Water Quality Agreement between the U.S.A. and Canada for connecting waters of the Great Lakes was not exceeded. At the other six locations where sediments were polluted, production was markedly lower (359 to 872 mg dry wt m-2). This finding is significant because it indicates that existing sediment quality criteria can be applied to protect H. limbata from oil, cyanide, and metals in the Great Lakes and connecting channels where the species fulfills a major role in secondary production and trophic transfer of energy.Contribution 733, of the National Fisheries Research Center-Great Lakes, U.S. Fish and Wildlife Service, 1451 Green Road, Ann Arbor, MI 48105. 相似文献
190.
Preservation of Tracheal Mucus by Nonaqueous Fixative 总被引:3,自引:0,他引:3
David E. Sims Jane A. Westfall Anthony L. Kiorpes Margaret M. Home 《Biotechnic & histochemistry》1991,66(4):173-180
Two nonaqueous fixatives, composed of fluorocarbon solvents with dissolved osmium tetroxide, were used to determine the feasibility of preserving the mucous coat in bovine and rat trachea for light and electron microscopy. Aqueous fixatives, while providing excellent cytological preservation, wash away the mucous lining, precluding ultrastructural analysis. Inclusion of ruthenium red or alcian blue within aqueous fixative improved retention of mucus, but provided incomplete, patchy results. Fixation with nonaqueous fluorocarbon solvent and dissolved osmium tetroxide preserved a continuous mucous epiphase layer above a clear hypophase layer. Subcomponents of the mucus included an electron dense surface layer, interrupted patches of mucus above the surface layer and electron dense membrane-like material within the mucus. This method of fixation will preserve mucus for light, scanning and transmission electron microscopy, using either intratracheal or immersion methods of fixation. The latter would enable use of materials from large animal models, autopsy or an abattoir. 相似文献