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51.
Enrique A. Gonzlez Froiln Vzquez Jos Ignacio Garabal Jorge Blanco 《Microbiology and immunology》1995,39(12):937-942
Fimbriae isolation by means of thermal shock was applied to fifteen K88-positive (three K88ab, nine K88ac and three K88ad) Escherichia coli reference strains belonging to serotypes O8:K87, O32, O45, O138:K81, O141:K85, O147:K89, O149:K91, and O157, as well as to ten K88-positive enterotoxigenic strains isolated from porcine diarrhea in Spain, all of them belonging to the O149 serogroup. Fimbriae were removed from the bacterial cells by thermal shock at 60 C and then precipitated using ammonium sulfate. The final amount of K88 antigen and the purification degree were not related to the serogroup of the bacteria or to the antigen variant but were related to the buffer used for isolation. Phosphate buffer containing urea was shown to be more effective than Tris-HCl for isolation of K88 antigen. The molecular weights by SDS-PAGE for K88ab, K88ac, and K88ad were 28.5, 29.2, and 31.0 kDa, respectively. All enterotoxigenic E. coli strains isolated in Spain showed the K88ac variant. 相似文献
52.
53.
Ernesto Bonilla Enrique Salazar Jose Joaquin Villasmil Ruddy Villalobos Magaly Gonzalez Jose Omar Davila 《Neurochemical research》1984,9(11):1543-1548
Copper concentration was determined in samples from 38 areas of 7 normal human brains. The grey matter contained higher concentrations of copper than the white matter. Identical areas of the grey and white matter of the cerebral cortex showed significant differences between individuals. In the caudate nucleus the highest concentrations of copper were found in the tail followed by the body and the head, respectively. A negative linear regression between age and brain copper levels was demonstrated. 相似文献
54.
Temporal integration of pungency 总被引:9,自引:4,他引:5
Four experiments explored possible temporal summation in olfactionand the common chemical sense. In one experiment, participantsjudged the perceived magnitude of various concentrations anddurations (1.253.75 s) of the pungent odorant ammoniaand the nonpungent odorant isoamyl butyrate. The perceived magnitudeof ammonia increased during an inhalation whereas the magnitudeof isoamyl butyrate did not. Time-intensity trading relationsfor ammonia indicated nearly perfect temporal summation. Inanother experiment, modulation of the concentration of ammoniaduring an inhalation led to assessments of perceived magnitudethat confirmed the high degree of temporal summation seen inthe first experiment. That is, approximately equal time-integratedmass of inhaled ammonia led to approximately equal perceivedintensity. A third experiment indicated that temporal summationfor ammonia arose from its pungency rather than from its odor,a fourth that trigeminally-mediated reflex apnea in responseto ammonia also exhibits temporal summation. The degree of temporalsummation measured with the reflex came very close to that assessedpsychophysically. When stimulated with ammonia, the common chemicalsense behaves more like a totalmass detector than a concentrationdetector. The investigation raises the possibility that theshortterm sensory reaction to most pungent stimuli may followthis simple rule. 相似文献
55.
The stimulation of poly(U)-directed polyphenylalanine synthesis produced by modification ofEscherichia coli ribosomes withp-hydroxymercuribenzoate, at low molar ratios of reagent to ribosomes, is due to an increase in the average chain length of polyphenylalanine synthesized, and not to the activation of inactive ribosomes. At a higher molar ratio ofp-hydroxymercuribenzoate to ribosomes, which produces no overall change in activity, approximately 50% of the active ribosomes present in the untreated preparation have been completely inactivated, and the remaining active ones, like the ribosomes of the stimulated preparation, synthesize polyphenylalanine at an increased rate as compared with the untreated ribosomes.Abbreviations pHMB
p-hydroxymercuribenzoate
- SucNBr
N-bromosuccinimide 相似文献
56.
Odor, taste, and flavor perception of some flavoring agents 总被引:1,自引:1,他引:0
Psychophysical functions for the odor, taste, and flavor offive common flavorings were obtained by the method of magnitudeestimation. The stimuli included three simple compounds (vanillin,piperonal, and benzaldehyde) and two complex ones (natural vanillaextract and artificial almond essence). The odor intensity ofall the flavorings grew much less rapidly with concentrationthan did taste intensity. The growth of flavor for the complexsubstances and piperonal behaved very much like taste. For vanillinand benzaldehyde, the flavor functions resembled taste functionsat high concentrations but showed a tendency to flatten at lowerconcentrations. These findings implied that, at least for someflavorings, the growth of flavor reflects the most salient featureon the particular concentration range studied. At low concentrationsodor seems to be the most important feature and so flavor functionsare generally flat, but at high concentrations taste becomesthe salient feature and so flavor functions steepen. 相似文献
57.
Enrique J. del Pino Marcelo O. Cabada María C. Fonio 《Molecular reproduction and development》1981,4(2):97-104
Various plant lecins were employed in cell agglutination experiments to ascertain the presence of specific saccharides in the surface of B arenarum and L chaquensis spermatozoa. B arenarum spermatozoa were specifically agglutinated with Concanavalin A (Con A), phytohemagglutinin P (PHA-P), and wheat germ agglutinin (WGA), but not with soybean agglutinin (SBA). In contrast, L chaquensis spermatozoa were strongly agglutinated by SBA, WGA, and PHA-P. L chaquensis spermatozoa did not agglutinate with Con A even at high concentrations. Lectinmediated sperm agglutination was inhibited in the presence of specific lectinbinding sugars. Spermatozoa from both species were agglutinated randomly with all lectins suggesting a uniform distribution in the sperm surface of the lectinbinding saccharide ligands. B arenarum sperm agglutination induced by Con A is sensitive to temperature. B arenarum spermatozoa are more agglutinable at 24°C than at 4°C. These results suggest that lectin-binding site mobility is necessary for sperm agglutination. 相似文献
58.
Angel López Piñeiro Enrique Saiz 《International journal of biological macromolecules》1983,5(1):37-41
The Rotational Isomeric States model is applied to calculate dipole moments of polypeptides of the twenty natural α-amino acids in the random coil state. Dipole moments of each repeat unit (μi), are evaluated using a quantum mechanics procedure. Dipole moment ratios () of homopolypeptides are calculated and extrapolated to x →?. With a few exceptions, D? = 0.36 ± 0.1. Ten actual proteins and three enzymes are also studied; their dipole ratios (Dx′ =〈μ〉/x) range from 7.34 to 10.57 in 10?59 C2 m2 (6.6–9.5 D2). Diffferences in the values of Dx′ are due mainly to the different contributions, μi, of the amino acid residues contained in each polymer, whereas the sequence of amino acids has a very minor effect. 相似文献
59.
60.
Insertion of a MalE β-Galactosidase Fusion Protein into the Envelope of Escherichia coli Disrupts Biogenesis of Outer Membrane Proteins and Processing of Inner Membrane Proteins 下载免费PDF全文
Enrique Herrero Maria Jackson Phillip J. Bassford David Sinden I. Barry Holland 《Journal of bacteriology》1982,152(1):133-139
The synthesis of a membrane-bound MalE β-galactosidase hybrid protein, when induced by growth of Escherichia coli on maltose, leads to inhibition of cell division and eventually a reduced rate of mass increase. In addition, the relative rate of synthesis of outer membrane proteins, but not that of inner membrane proteins, was reduced by about 50%. Kinetic experiments demonstrated that this reduction coincided with the period of maximum synthesis of the hybrid protein (and another maltose-inducible protein, LamB). The accumulation of this abnormal protein in the envelope therefore appeared specifically to inhibit the synthesis, the assembly of outer membrane proteins, or both, indicating that the hybrid protein blocks some export site or causes the sequestration of some limiting factor(s) involved in the export process. Since the MalE protein is normally located in the periplasm, the results also suggest that the synthesis of periplasmic and outer membrane proteins may involve some steps in common. The reduced rate of synthesis of outer membrane proteins was also accompanied by the accumulation in the envelope of at least one outer membrane protein and at least two inner membrane proteins as higher-molecular-weight forms, indicating that processing (removal of the N-terminal signal sequence) was also disrupted by the presence of the hybrid protein. These results may indicate that the assembly of these membrane proteins is blocked at a relatively late step rather than at the level of primary recognition of some site by the signal sequence. In addition, the results suggest that some step common to the biogenesis of quite different kinds of envelope protein is blocked by the presence of the hybrid protein. 相似文献