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排序方式: 共有90条查询结果,搜索用时 15 毫秒
1.
Levans produced by four Zymomonas mobilis strains showed antitumour activity against sarcoma 180 and Ehrlich carcinoma in Swiss albino mice. Levans from two strains (ZAP and CP4) had the highest effects. NMR analysis showed that the polymers were composed only of fructose units. The results suggested that the antineoplasic effect is associated to the polysaccharide molecular weight and that a particular molecular weight range may be responsible for this effect. 相似文献
2.
Filippo Aureli Marjolijn Das Désirée Verleur Jan A. R. A. M. van Hooff 《International journal of primatology》1994,15(3):471-485
We investigated the occurrence of postconflict social interactions in a group of Barbary macaques (Macaca sylvanus)that live in a large enclosure. We collected data during the mating and the nonmating seasons and analyzed them via two methods.
Separate analyses for the two seasons yielded very similar results. Reconciliation and redirection occurred. But we found
no evidence for consolation and postconflict kin-oriented affiliation. The consistency of these findings with those on other
species of Macacaindicates that reconciliation and redirection are typical postconflict social interactions of macaque victims. 相似文献
3.
Marjolijn J. A. Christianen Fee O. H. Smulders Jan Arie Vonk Leontine E. Becking Tjeerd J. Bouma Sabine M. Engel Rebecca K. James Mabel I. Nava Jaco C. de Smit Jurjan P. van der Zee Per J. Palsbøll Elisabeth S. Bakker 《Global Change Biology》2023,29(1):215-230
Large grazers (megaherbivores) have a profound impact on ecosystem functioning. However, how ecosystem multifunctionality is affected by changes in megaherbivore populations remains poorly understood. Understanding the total impact on ecosystem multifunctionality requires an integrative ecosystem approach, which is especially challenging to obtain in marine systems. We assessed the effects of experimentally simulated grazing intensity scenarios on ecosystem functions and multifunctionality in a tropical Caribbean seagrass ecosystem. As a model, we selected a key marine megaherbivore, the green turtle, whose ecological role is rapidly unfolding in numerous foraging areas where populations are recovering through conservation after centuries of decline, with an increase in recorded overgrazing episodes. To quantify the effects, we employed a novel integrated index of seagrass ecosystem multifunctionality based upon multiple, well-recognized measures of seagrass ecosystem functions that reflect ecosystem services. Experiments revealed that intermediate turtle grazing resulted in the highest rates of nutrient cycling and carbon storage, while sediment stabilization, decomposition rates, epifauna richness, and fish biomass are highest in the absence of turtle grazing. In contrast, intense grazing resulted in disproportionally large effects on ecosystem functions and a collapse of multifunctionality. These results imply that (i) the return of a megaherbivore can exert strong effects on coastal ecosystem functions and multifunctionality, (ii) conservation efforts that are skewed toward megaherbivores, but ignore their key drivers like predators or habitat, will likely result in overgrazing-induced loss of multifunctionality, and (iii) the multifunctionality index shows great potential as a quantitative tool to assess ecosystem performance. Considerable and rapid alterations in megaherbivore abundance (both through extinction and conservation) cause an imbalance in ecosystem functioning and substantially alter or even compromise ecosystem services that help to negate global change effects. An integrative ecosystem approach in environmental management is urgently required to protect and enhance ecosystem multifunctionality. 相似文献
4.
Variation in the ribosomal internal transcribed spacers (ITS1 and ITS2) among eight taxa of the Mimulus guttatus species complex 总被引:1,自引:0,他引:1
The internal transcribed spacer region (ITS1 and ITS2) of the 18S-25S
nuclear ribosomal DNA sequence and the intervening 5.8S region were
sequenced from three individuals in each of eight taxa of the Mimulus
guttatus species complex. Three discrete variants, or "types," of ITS
sequences were found, among which 30%-40% of sites differed, compared with
1%-2% within types. Dot plots indicate that these types were not related by
conspicuous rearrangements or inversions. More than one ITS type was often
found in the same taxon, and two of three ITS types span species
boundaries, indicating their presence prior to speciation. These ITS
sequences showed essentially no positional homology with the nearest
sequenced relative, tomato. In contrast, the 5.8S region was relatively
unvaried, with 8 of 162 sites varied in the sample among all eight taxa.
The phylogeny inferred by the most common ITS sequence type, rooted by the
two other ITS types, agreed with isozymes in showing the distinctness of M.
nudatus, M. laciniatus, and M. tilingii from the other five taxa.
相似文献
5.
Variation in heat shock proteins within tropical and desert species of poeciliid fishes 总被引:8,自引:0,他引:8
Norris CE; diIorio PJ; Schultz RJ; Hightower LE 《Molecular biology and evolution》1995,12(6):1048-1062
The 70-kilodalton heat shock protein (hsp70) family of molecular
chaperones, which contains both stress-inducible and normally abundant
constitutive members, is highly conserved across distantly related taxa.
Analysis of this protein family in individuals from an outbred population
of tropical topminnows, Poeciliopsis gracilis, showed that while
constitutive hsp70 family members showed no variation in protein isoforms,
inducibly synthesized hsp70 was polymorphic. Several species of
Poeciliopsis adapted to desert environments exhibited lower levels of
inducible hsp70 polymorphism than the tropical species, but constitutive
forms were identical to those in P. gracilis, as they were in the
confamilial species Gambusia affinis. These differences suggest that
inducible and constitutive members of this family are under different
evolutionary constraints and may indicate differences in their function
within the cell. Also, northern desert species of Poeciliopsis synthesize a
subset of the inducible hsp70 isoforms seen in tropical species. This
distribution supports the theory that ancestral tropical fish migrated
northward and colonized desert streams; the subsequent decrease in
variation of inducible hsp70 may have been due to genetic drift or a
consequence of adaptation to the desert environment. Higher levels of
variability were found when the 30- kilodalton heat shock protein (hsp30)
family was analyzed within different strains of two desert species of
Poeciliopsis and also in wild-caught individuals of Gambusia affinis. In
both cases the distribution of hsp30 isoform diversity was similar to that
seen previously with allozyme polymorphisms.
相似文献
6.
Clinical phenotype of nephrogenic diabetes insipidus in females heterozygous for a vasopressin type 2 receptor mutation 总被引:2,自引:0,他引:2
Angenita F. van Lieburg Marian A. J. Verdijk Frans Schoute Marjolijn J. L. Ligtenberg Bernard A. van Oost Franz Waldhauser Maria Dobner Leo A. H. Monnens Nine V. A. M. Knoers 《Human genetics》1995,96(1):70-78
Nephrogenic diabetes insipidus (NDI) usually shows an X-linked recessive mode of inheritance caused by mutations in the vasopressin type 2 receptor gene (AVPR2). In the present study, three NDI families are described in which females show clinical features resembling the phenotype in males. Maximal urine osmolality in three female patients did not exceed 200 mosmol/kg and the absence of extra-renal responses to 1-desamino-8-d-arginine vasopressin was demonstrated in two of them. All affected females and two asymptomatic female family members were shown to be heterozygous for an AVPR2 mutation. Skewed X-inactivation is the most likely explanation for the clinical manifestation of NDI in female carriers of an AVPR2 mutation. It is concluded that, in female NDI patients, the possibility of heterozygosity for an AVPR2 gene mutation has to be considered in addition to homozygosity for mutations in the aquaporin 2 gene. 相似文献
7.
Comparison of the effects of inhibitors of cytochrome P-450-mediated reactions on human platelet aggregation and arachidonic acid metabolism 总被引:2,自引:0,他引:2
Metyrapone and SKF-525A, together with amphenone B, a structural analogue of metyrapone, which are all inhibitors of cytochrome P-450-mediated reactions, were shown to inhibit the arachidonic acid-induced aggregation of human platelets. Amphenone B, like metyrapone, exhibited a type II (ligand) binding spectrum with rat liver microsomal cytochrome P-450, in contrast to SKF 525A which is a type I (substrate) binding agent. Independently of their type of binding spectra and of their maximum spectral change, however, the affinity of the three compounds for rat liver cytochrome P-450 showed a close proportional correlation with their platelet aggregation inhibitory potency. All three compounds inhibited the formation of [1-14C]thromboxane B2 from [1-14C]arachidonic acid by human platelets aggregated with collagen. The effect of metyrapone on the remaining labelled products suggested that it is a selective thromboxane synthesis inhibitor, while amphenone B exhibited activity reminiscent of cyclo-oxygenase inhibitors. SKF 525A produced complex effects possibly attributable to cyclo-oxygenase inhibition and enhanced lipid peroxidation, since it also enhanced platelet malonaldehyde formation, which the other two compounds inhibited. These data provide further support for a role of cytochrome P-450 in thromboxane synthesis and platelet aggregation. 相似文献
8.
de Brouwer AP Pennings RJ Roeters M Van Hauwe P Astuto LM Hoefsloot LH Huygen PL van den Helm B Deutman AF Bork JM Kimberling WJ Cremers FP Cremers CW Kremer H 《Human genetics》2003,112(2):156-163
We have ascertained a multi-generation family with apparent autosomal recessive non-syndromic childhood hearing loss (DFNB). Failure to demonstrate linkage in a genome-wide scan with 300 polymorphic markers has suggested genetic heterogeneity for the hearing loss in this family. This heterogeneity could be demonstrated by analysis of candidate loci and genes for DFNB. Patients in one branch of the family (branch C) are homozygous for the 35delG mutation in the GJB2 gene (DFNB1). Patients in two other branches (A and B) carry two new mutations in the cadherin 23 ( CDH23) gene (DFNB12). A homozygous CDH23 c.6442G-->A (D2148N) mutation is present in branch A. Patients in branch B are compound heterozygous for this mutation and the c.4021G-->A (D1341N) mutation. The substituted aspartic acid residues are highly conserved and are part of the calcium-binding sites of the extracellular cadherin (EC) domains. Molecular modeling of the mutated EC domains of CDH23 based on the structure of E-cadherin indicates that calcium-binding is impaired. In addition, other aspartic and glutamic acid residue substitutions in the highly conserved calcium-binding sites reported to cause DFNB12 are also likely to result in a decreased affinity for calcium. Since calcium provides rigidity to the elongated structure of cadherin molecules enabling homophilic lateral interaction, these mutations are likely to impair interactions of CDH23 molecules either with CDH23 or with other proteins. DFNB12 is the first human disorder that can be attributed to inherited missense mutations in the highly conserved residues of the extracellular calcium-binding domain of a cadherin. 相似文献
9.
10.
Maurits S. Buiten Mihály K. de Bie Joris I. Rotmans Friedo W. Dekker Marjolijn van Buren Ton J. Rabelink Christa M. Cobbaert Martin J. Schalij Arnoud van der Laarse J. Wouter Jukema 《PloS one》2015,10(8)