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31.
Dr. María Cristina Maldonado Ana María Strasser de Saad Danley Callieri 《Current microbiology》1989,18(5):303-306
Several recent reports have described large numbers of monoclonal antibodies that cross-react with toxins A and B ofClostridium difficile; this suggests that the toxins share major epitopes. Our results show that monoclonal antibodies (MAb) against other antigens bind nonspecifically to both toxins. Therefore, we believe that the cross-reacting MAb bind by this manner and not by a true immune reaction. 相似文献
32.
Stephen Francis Ferrari Maria Aparecida Lopes Ferrari 《Primates; journal of primatology》1990,31(3):323-338
The predator avoidance behaviour of a free-ranging group of buffy-headed marmosets,Callithrix flaviceps, was recorded in detail during the course of a long-term study of behavioural ecology at the Fazenda Montes Claros, southeastern
Brazil. Four distinct patterns of predator avoidance behaviour, each with specific vocalisations, were recognised and are
described here. The selection and use of sleeping sites by the study group are also described. An analysis of the records
indicates that these small monkeys are generally most vulnerable to predation by aerial raptors. Variations in the frequency
of alarm calls also indicate that the marmosets tend to be more vigilant at higher levels in the forest and when the leaf
cover is less extensive. The implications of group size and social structure for both the evolution and the efficacy of the
anti-predator behaviour of marmosets are also discussed. 相似文献
33.
Marcelo Hermes-Lima Ana Claudia Tessis Adalberto Vieyra 《Origins of life and evolution of the biosphere》1990,20(1):27-41
In this paper it is shown that the adsorption of 5-adenosine monophosphate (5-AMP) onto precipitated calcium phosphate exhibits a sigmoidal profile as revealed by isotherms at 45 °C. This result indicates a cooperative behavior in the adsorption of 5-AMP. The relationship between adsorption capacity and surface area of the sedimented matrix may be interpreted as an indication that there is a monolayer of the adsorbed nucleotide on the solid surface. The pH dependence of adsorption suggests that the negatively charged phosphoryl group of 5-AMP interacts with a positively charged site (possibly Ca2+) on the matrix surface. The adsorption of the nucleotide is markedly decreased at pH values above 8.0. The Dixon-like plot of the effect of pH suggests an inhibitory role of hydroxyl ions in the adsorption of 5-AMP. At pH 7.5, other anions such as pyrophosphate, tripolyphosphate and carbamyl phosphate also inhibit the adsorption of the nucleotide, probably by interacting with its adsorption site. We suggest that these phosphorylated molecules could have played a role in chemical evolution by modulating the amount of nucleotides adsorbed onto mineral surfaces. The significance of these phenomena in chemical evolution is discussed. 相似文献
34.
Ana M. Moura-da-Silva R. David G. Theakston Julian M. Cramptonl 《Journal of molecular evolution》1996,43(3):263-269
The evolution of the Metalloproteinase Disintegrin Cysteine-rich (MDC) gene family and that of the mammalian Matrix-degrading
Metalloproteinases (MMPs) are compared. The alignment of snake venom and mammalian MDC and MMP precursor sequences generated
a phylogenetic tree that grouped these proteins mainly according to their function. Based on this observation, a common ancestry
is suggested for mammalian and snake venom MDCs; it is also possible that gene duplication of the already-assembled domain
structure, followed by divergence of the copies, may have significantly contributed to the evolution of the functionally diverse
MDC proteins. The data also suggest that the structural resemblance of the zinc-binding motif of venom MDCs and MMPs may best
be explained by common ancestry and conservation of the proteolytic motifs during the divergence of the proteins rather than
through convergent evolution.
Correspondence to: J.M. Crampton 相似文献
35.
Claudia Gaspar Iscia Lopes-Cendes Anita L. DeStefano Patrícia Maciel Isabel Silveira Paula Coutinho Patrick MacLeod Jorge Sequeiros Lindsay A. Farrer G. A. Rouleau 《Human genetics》1996,98(5):620-624
Machado-Joseph disease (MJD) is an autosomal dominant spinocerebellar degeneration originally described in families of Portuguese-Azorean
ancestry. The hypothesis that its present world distribution could result from the spread of an original founder mutation
has been raised. To test this possibility we have conducted a linkage disequilibrium study of markers segregating with the
MJD1 locus in a total of 64 unrelated families of different geographical origins. Significant association was detected between
the MJD1 locus and marker alleles at loci D14S280, D14S1050 and D14S81. All affected individuals, except one Chinese family, had allele
3 (237 bp) at D14S280. This finding is consistent with a founder effect in our MJD population. However, distinct haplotypes
were observed in patients originating from the two Azorean islands showing the highest disease prevalence; therefore, the
possible existence of more than one founder mutation can not be excluded with the markers currently available.
Received: 27 February 1996 / Revised: 4 June 1996 相似文献
36.
Márcia Camargo-De-Morais Marta De Freitas Angela G. De Mattos Nádia Schröder Ana C. Zilles Carla S. F. Lisboa Nice Arteni Armando Barlem Rejane Schierholt Guilherme Zwetsch Carlos A. B. Souza Regina Pessoa-Pureur Carlos A. Netto 《Neurochemical research》1996,21(5):595-602
Neurofilaments subunits (NF-H, NF-M, NF-L) and glial fibrillary acidic protein (GFAP) were investigated in the hippocampus
of rats after distinct periods of reperfusion (1 to 15 days) following 20 min of transient global forebrain ischemia in the
rat. In vitro [14Ca]leucine incorporation was not altered until 48 h after the ischemic insult, however concentration of intermediate filament
subunits significantly decreased in this period. Three days after the insult, leucine incorporation significantly increased
while the concentration NF-H, NF-M, and NF-L were still diminished after 15 days of reperfusion. In vitro incorporation of32P into NF-M and NF-L suffered immediately after ischemia, but returned to control values after two days of reperfusion. GFAP
levels decreased immediately after ischemia but quickly recovered and significantly peaked from 7 to 10 days after the insult.
These results suggest that transient ischemia followed by reperfusion causes proteolysis of intermediate filaments in the
hippocampus, and that proteolysis could be facilitated by diminished phosphorylation levels of NF-M and NF-L. 相似文献
37.
Neural control of the expression of a Ca2+-activated K+ channel involved in the induction of myotonic-like characteristics 总被引:2,自引:0,他引:2
Beatriz U. Ramírez Maria Isabel Behrens Cecilia Vergara 《Cellular and molecular neurobiology》1996,16(1):39-49
Summary 1. Expression of the apamin-sensitive K+ channel (SK+) in rat skeletal muscle is neurally regulated. The regulatory effect of the nerve over the expression of some muscle ion
channels has been attributed to the electrical activity triggered by the nerve and/or to a trophic effect of some molecules
transported from the soma to the axonal endings.
2. SK+ channels apparently are involved in myotonic dystrophy (MD), therefore understanding the factors that regulate their expression
may ultimately have important clinical relevance.
3. To establish if axoplasmic transport is involved in this process, we used two experimental approaches in adult rats: (a)
Both sciatic nerves were severed, leaving a short or a long nerve stump attached to the anterior tibialis (AT). (b) Colchicine
or vinblastine (VBL), two axonal transport blockers of different potencies, was applied on one leg to the sciatic nerve. To
determine whether electrical activity affects the expression of SK+ channels, denervated AT were directly stimulated. The corresponding contralateral muscles were used as controls.
4. With these experimental conditions we measured (a) apamin binding to muscle membranes, (b) muscle contractile characteristics,
and (c) electromyographic activity.
5. In the short- and long-nerve stump experiments, 5 days after denervation125I-apamin binding to AT membranes was 2.0 times higher in the short-stump side. This difference disappeared at longer times.
The delayed expression of SK+ channels in the muscle left with a longer nerve stump can be attributed to the extra axoplasm contained in the longer stump,
which maintains a normally repressive signal for a longer period of time. Ten to 15 days after application of axonal transport
blockers we found that the muscle half-relaxation time increased in the drug-treated side and apamin partially reverted the
prolonged relaxation. Myotonic-like discharges specifically blockable by apamin were always present in the drug-treated leg.125I-Apamin binding, which is undetectable in a microsomal preparation from hind leg control muscles, was increased in the drug-treated
preparations. Apamin binding to denervated and stimulated AT muscles was lower than in the contralateral unstimulated muscles
[3.3±1.0 vs 6.8±0.8 (n=4) fmol/mg protein].
6. Our results demonstrate that electrical activity and axoplasmic transport are involved in the control of expression of
SK+ in rat skeletal muscle. However, the increased expression of this channel induces myotonic-like characteristics that are
reversed by apamin. This myotonic activity could be a model for MD. 相似文献
38.
Joaquin Royo Isabel Diaz Pablo Rodriquez-Palenzuela Pilar Carbonero 《Plant molecular biology》1996,31(5):1051-1059
The geneItr1, encoding trypsin inhibitor BTI-CMe, has been obtained from a genomic library ofHordeum vulgare L. The gene has no introns and presents in its 5-upstream region 605 bp that are homologous to the long terminal repeats (LTR) of the copia-like retro-transposon Bare-1. Functional analysis of theItr1 promoter by transient expression in protoplasts derived from different barley tissues, has shown that in this system theItr1 promoter retains its endosperm specifity and thetrans-regulation mediated by theLys3a gene. The proximal promoter extending 343 bp upstream of the translation initiation ATG codon is sufficient to confer fullGUS expression and for endosperm specifity. In protoplasts derived from thelys3a mutant, Risø 1508,GUS activity was less than 5% of that obtained with the same constructs in the protoplasts of wild-type Bomi from which it derives. Gel retardation experiments, after incubation with proteins obtained from both types of endosperm nuclei, also show differential patterns. Possible reasons for these differences are discussed.Equal authours 相似文献
39.
Isabel Allona Carmen Collada Rosa Casado Javier Paz-Ares Cipriano Aragoncillo 《Plant molecular biology》1996,32(6):1171-1176
Ch3, an endochitinase of 32 kDa present in Castanea sativa cotyledons, showed in vitro antifungal properties when assayed against Trichoderma viride. The characterization of a cDNA clone corresponding to this protein indicated that Ch3 is a class Ib endochitinase that is synthesized as a preprotein with a signal sequence preceding the mature polypeptide. Bacterial expression of mature Ch3 fused to the leader peptide of the periplasmic protein ompT resulted in active Ch3 enzyme. A plate assay was adapted for semi-quantitative determination of chitinase activity secreted from cultured bacteria, which should facilitate the identification of mutants with altered capacity to hydrolyse chitin. 相似文献
40.
Ana María Planchuelo 《Brittonia》1996,48(2):263-265
Lupinus rubriflorus Planchuelo, from Rio Grande do Sul, Brazil, is described and illustrated. This species is related toL. bracteolaris s.l. differing in pubescence, stipules, and floral characters. 相似文献