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1.
Computer-aided image-averaging methods are applied to different preparations of membrane-bound nicotinic acetylcholine receptor. Circular harmonic averaging (CHA), a novel, reference-independent averaging method developed by W. Kunath and H. Sack-Kongehl [1989) Ultramicroscopy 27:171-184) allows analyzing images of single molecules of the receptor in its native membrane-bound state. The five subunits of the receptor are clearly resolved. At the resolution obtained (approximately 20 A) no differences were observed with resting and agonist-desensitized receptors. A method is proposed for rapidly arranging the acetylcholine receptors to ordered lattices. Depending on the conditions, tetragonal or hexagonal, two-dimensional lattices can be obtained within 2 to 6 days at 4 degrees C. Analysis by CHA shows that the receptor molecules preserve their gross structure and dimensions in these membranes, but that they are randomly oriented. Both lattices, therefore, do not represent true two-dimensional crystals. 相似文献
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A comparative description of mitochondrial DNA differentiation in selected avian and other vertebrate genera 总被引:14,自引:1,他引:13
Levels of mitochondrial DNA (mtDNA) sequence divergence between species
within each of several avian (Anas, Aythya, Dendroica, Melospiza, and
Zonotrichia) and nonavian (Lepomis and Hyla) vertebrate genera were
compared. An analysis of digestion profiles generated by 13-18 restriction
endonucleases indicates little overlap in magnitude of mtDNA divergence for
the avian versus nonavian taxa examined. In 55 interspecific comparisons
among the avian congeners, the fraction of identical fragment lengths (F)
ranged from 0.26 to 0.96 (F = 0.46), and, given certain assumptions, these
translate into estimates of nucleotide sequence divergence (p) ranging from
0.007 to 0.088; in 46 comparisons among the fish and amphibian congeners, F
values ranged from 0.00 to 0.36 (F = 0.09), yielding estimates of P greater
than 0.070. The small mtDNA distances among avian congeners are associated
with protein-electrophoretic distances (D values) less than approximately
0.2, while the mtDNA distances among assayed fish and amphibian congeners
are associated with D values usually greater than 0.4. Since the
conservative pattern of protein differentiation previously reported for
many avian versus nonavian taxa now appears to be paralleled by a
conservative pattern of mtDNA divergence, it seems increasingly likely that
many avian species have shared more recent common ancestors than have their
nonavian taxonomic counterparts. However, estimates of avian divergence
times derived from mtDNA- and protein-calibrated clocks cannot readily be
reconciled with some published dates based on limited fossil remains. If
the earlier paleontological interpretations are valid, then protein and
mtDNA evolution must be somewhat decelerated in birds. The empirical and
conceptual issues raised by these findings are highly analogous to those in
the long-standing debate about rates of molecular evolution and times of
separation of ancestral hominids from African apes.
相似文献
4.
A M Signorini M Bandini I Tanganelli G Gragnoli 《Bollettino della Società italiana di biologia sperimentale》1984,60(7):1347-1353
The determination of glycosylated albumin was performed in 19 diabetic patients and in 16 control subjects, by means of chromatographic separation on columns of phenilboronic acid, immobilized by agarose gel. The interference with free glucose was eliminated by serum gel filtration on sephadex G 25 columns. The results demonstrated that glycosylated albumin values, obtained by affinity chromatography, discriminate diabetic by non-diabetic subjects and significantly correlate with glycosylated proteins levels, taken by colorimetric method with thiobarbituric acid. The chromatographic technique resulted in a more simplified way than colorimetric method and has shown to be sensitive to significant increases in "in vitro" glycosylation. Moreover it lasts less than the other technique and its variation coefficient is extremely low. In conclusion it represents a progress in the routine determination of glycosylated albumin. 相似文献
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Dubey JP Alvarado-Esquivel C Liesenfeld O Herrera-Flores RG Ramírez-Sánchez BE González-Herrera A Martínez-García SA Bandini LA Kwok OC 《The Journal of parasitology》2007,93(5):1033-1035
Toxoplasma gondii and Neospora caninum are structurally similar parasites, with many hosts in common. The prevalence of antibodies to T. gondii and N. caninum was determined in sera from dogs from Durango City, Mexico. Using a modified agglutination test, antibodies to T. gondii were found in 52 (51.5%) of the 101 dogs with titers of 1:25 in 27, 1:50 in 11, 1:100 in 5, 1:200 in 4, 1:400 in 2, 1:800 in 2, and 1:3,200 or higher in 1. Antibodies to N. caninum were determined by the indirect immunofluorescent antibody test (IFAT) and the Neospora sp. agglutination test (NAT). Two of the 101 dogs had N. caninum antibodies; these dogs did not have T. gondii antibodies, supporting the specificity of the tests used. The N. caninum antibody titers of the 2 dogs were: 1:400 by IFAT and 1:200 by NAT in 1, and 1:25 by NAT and IFAT in the other. Results indicate that these 2 structurally similar protozoans are antigenically different. 相似文献
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A new valuable catalytic protocol for the preparation of synthetically useful beta-indolyl nitro compounds bearing benzhydryl stereocenters is presented. The combined use of catalytic amounts of a commercially available chiral [SalenAlCl] complex and pyridine allowed, for the Friedel-Crafts alkylation reaction of indoles with aromatic nitro-olefins to be carried out in good yields and enantioselectivity (up to 63% ee). 相似文献
8.
Sarah M. Phillips Linda G. Bandini Elena N. Naumova Helene Cyr Skye Colclough William H. Dietz Aviva Must 《Obesity (Silver Spring, Md.)》2004,12(3):461-472
Objective: The longitudinal relationship between the consumption of energy‐dense snack (EDS) foods and relative weight change during adolescence is uncertain. Using data from the Massachusetts Institute of Technology Growth and Development Study, the current analysis was undertaken to examine the longitudinal relationship of EDS food intake with relative weight status and percentage body fat and to examine how EDS food consumption is related to television viewing. Research Methods and Procedures: One hundred ninety‐six nonobese premenarcheal girls 8 to 12 years old were enrolled between 1990 and 1993 and followed until 4 years after menarche. At each annual follow‐up visit, data were collected on percentage body fat (%BF), BMI z score, and dietary intake. Categories of EDS foods considered were baked goods, ice cream, chips, sugar‐sweetened soda, and candy. Results: At study entry, girls had a mean ± SD BMI z score of ?0.27 ± 0.89, consumed 2.3 ± 1.7 servings of EDS foods per day, and consumed 15.7 ± 8.1% of daily calories from EDS foods. Linear mixed effects modeling indicated no relationship between BMI z score or %BF and total EDS food consumption. Soda was the only EDS food that was significantly related to BMI z score over the 10‐year study period, but it was not related to %BF. In addition, a significant, positive relationship was observed between EDS food consumption and television viewing. Discussion: In this cohort of initially nonobese girls, overall EDS food consumption does not seem to influence weight status or fatness change over the adolescent period. 相似文献
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