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51.
Phylogenetic relationships among prokaryotic and eukaryotic catalases 总被引:13,自引:1,他引:12
Seventy-four catalase protein sequences, including 29 bacterial, 8 fungal,
7 animal, and 30 plant sequences, were compiled, and 70 were used for
phylogenetic reconstruction. The core of the resulting tree revealed
unique, separate groups of plant and animal catalases, two groups of fungal
catalases, and three groups of bacterial catalases. The only overlap of
kingdoms occurred within one branch and involved fungal and bacterial
large-subunit enzymes. The other fungal branch was closely linked to the
group of animal enzymes. Group I bacterial catalases were more closely
related to the plant enzymes and contained such diverse taxa as the
Gram-positive Listeria seeligeri, Deinocococcus radiodurans, and
gamma-proteobacteria. Group III bacterial sequences were more closely
related to fungal and animal sequences and included enzymes from a broad
range of bacteria including high- and low-GC Gram positives,
proteobacteria, and a bacteroides species. Group II was composed of
large-subunit catalases from diverse sources including Gram positives
(low-GC Bacilli and high-GC Mycobacteria), proteobacteria, and species of
the filamentous fungus Aspergillus. These data can be interpreted in terms
of two gene duplication events that produced a minimum of three catalase
gene family members that subsequently evolved in response to environmental
demands. Horizontal gene transfer may have been responsible for the group
II mixture of bacterial and fungal large-subunit catalases.
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52.
53.
Sequence variation in the guillemot (Alcidae: Cepphus) mitochondrial control region and its nuclear homolog 总被引:4,自引:0,他引:4
We describe sequence variation in the mitochondrial control region and its
nuclear homolog in three species and seven subspecies of guillemots
(Cepphus spp.). Nuclear homologs of the 5' end of the control region were
found in all individuals. Nuclear sequences were approximately 50%
divergent from their mitochondrial counterparts and formed a distinct
phylogenetic clade; the mitochondrial-nuclear introgression event must have
predated the radiation of Cepphus. As in other vertebrates, the guillemot
control region has a relatively conserved central block flanked by
hypervariable 5' and 3' ends. Mean pairwise interspecific divergence values
among control regions were lower than those in other birds. All individuals
were heteroplasmic for the number of simple tandem nucleotide repeats
(A(n)C) at the 3' end of the control region. Phylogenetic analyses suggest
that black guillemots are basal to pigeon and spectacled guillemots, but
evolutionary relationships among subspecies remain unresolved, possibly due
to incomplete lineage sorting. Describing molecular variation in nuclear
homologs of mitochondrial genes is of general interest in phylogenetics
because, if undetected, the homologs may confound interpretations of
mitochondrial phylogenies.
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54.
A phylogenetic survey using the polymerase chain reaction (PCR) has
identified four major P element subfamilies in the saltans and willistoni
species groups of Drosophila. One subfamily, containing about half of the
sequences studied, consists of elements that are very similar to the
canonical (and active) P element from D. melanogaster. Within this
subfamily, nucleotide sequence differentiation among different copies from
the same species and among elements from different species is relatively
low. This observation suggests that the canonical elements are relatively
recent additions to the genome or, less likely, are evolving slowly
relative to the other subfamilies. Elements belonging to the three
noncanonical lineages are distinct from the canonical elements and from one
another. Furthermore, there is considerably more sequence variation, on the
average, within the noncanonical subfamilies compared to the canonical
elements. Horizontal transfer and the coexistence of multiple,
independently evolving element subfamilies in the same genome may explain
the distribution of P elements in the saltans and willistoni species
groups. Such explanations are not mutually exclusive, and each may be
involved to varying degrees in the maintenance of P elements in natural
populations of Drosophila.
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55.
Pig Reticulocytes. III. Glucose permeability in naturally occurring reticulocytes and red cells from newborn piglets 总被引:1,自引:1,他引:0
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The loss of facilitated glucose transport of red cells occurring in the newborn pig was monitored in 11 density-separated cells from birth to a 4 wk of age. At birth there was a threefold increase in glucose permeability from the lightest cells to the most dense, suggesting that cells having progressively less glucose permeability are released into the circulation as gestation proceeds. Because of extraordinary stimulation of erythropoietic activity, the uppermost top fraction constituting 2-3 percent of the total cells is composed purely of reticulocytes in the growing animal. The glucose permeability of these reticulocytes which at birth has a slow but significant rate of 3.7 μmol/ml cell x min at 25 degrees C is rapidly decreased within 3-4 days to the level of reticulocytes produced in the adult in response to phenylhydrazine assault. Moreover, reticulocytes themselves discard their membrane permeability to glucose in the course of maturation to red cells. Thus, even though reticulocytes at birth are permeable to glucose, they will become red cells practically impervious to glucose within a few days. These findings suggest that the transition from a glucose- permeable fetal state to a glucose-impermeable postnatal state is brought about by two mechanisms: (a) dilution of fetal cells by glucose-impervious cells produced coincidentally with or shortly after birth; and (b) elimination of fetal cells, which have a shorter half-life, from the circulation. 相似文献
56.
Brennan FM Smith NM Owen S Li C Amjadi P Green P Andersson A Palfreeman AC Hillyer P Foey A Beech JT Feldmann M 《Arthritis research & therapy》2008,10(2):R36-13
Background
Previously we described a system whereby human peripheral blood T cells stimulated for 8 days in a cytokine cocktail acquired effector function for contact-dependent induction of proinflammatory cytokines from monocytes. We termed these cells cytokine-activated (Tck) cells and found that the signalling pathways elicited in the responding monocytes were identical whether they were placed in contact with Tck cells or with T cells isolated from rheumatoid arthritis (RA) synovial tissue.Methods
Here, using magnetic beads and fluorescence-activated cell sorting, we extensively phenotype the Tck effector cells and conclude that effector function resides within the CD4+CD45RO+, CCR7-, CD49dhigh population, and that these cells are derived from the effector memory CD4+ T cells in resting blood.Results
After stimulation in culture, these cells produce a wide range of T-cell cytokines, undergo proliferation and differentiate to acquire an extensively activated phenotype resembling RA synovial T cells. Blocking antibodies against CD69, CD18, or CD49d resulted in a reduction of tumour necrosis factor-α production from monocytes stimulated with CD4+CD45RO+ Tck cells in the co-culture assay. Moreover, blockade of these ligands also resulted in inhibition of spontaneous tumour necrosis factor-α production in RA synovial mononuclear cell cultures.Conclusion
Taken together, these data strengthen our understanding of T-cell effector function, highlight the multiple involvement of different cell surface ligands in cell-cell contact and, provide novel insights into the pathogenesis of inflammatory RA disease. 相似文献57.
Previous studies have indicated that peripheral administration of interleukin-6 (IL-6) increases brain concentrations of tryptophan and 5-hydroxyindoleacetic acid (5-HIAA), the major catabolite of serotonin (5-HT). To determine whether these changes were related to increased synaptic release of 5-HT, we studied the responses to peripheral administration of IL-6 by in vivo microdialysis and in vivo amperometry. Intraperitoneal injection of recombinant IL-6 resulted in an elevation of microdialysate concentrations of 5-HT in the rat striatum. Also, amperometric measurements indicated that i.p. IL-6 enhanced the 5-HT-like signal obtained from the striatum following electrical stimulation of the dorsal raphe nucleus. These results indicate that the increases in brain concentrations of 5-HIAA observed in earlier studies indeed reflect increased synaptic release of 5-HT. 相似文献
58.
5-Aminolevulinic acid (ALA), a precursor of porphyrin synthesis, increased the production of various porphyrin compounds in Candida guilliermondii cells. Metalloporphyrins and protoporphyrin IX (PPIX) were predominantly accumulated, respectively, at ALA concentrations of 0.2-0.4 mM and at those higher than 1.5 mM. 2,2;-Dipyridyl which complexed with bivalent metals significantly increased the content of endogenous PPIX even at ALA concentrations lower than 0.5 mM. Under these conditions, the yeast sensitivity to photodynamic effect of visible light (400-600 nm) dramatically increased due to photosensitization by endogenous PPIX. 相似文献