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51.
Abstract: An enzymic activity of rat brain that liberates radioactive free aldehydes from 1-[1-14 C]alk-1'-enyl- sn -glycero-3-phosphoethanolamine (lysoplasmalogen) is described. It was present mainly in microsomal fractions (crude) of brains of rats of different ages. The highest specific enzyme activity was found in 21-day-old animals. The formation of free aldehyde was dependent on the amount of enzyme protein as well as the amount of substrate added, and was linear to the incubation time up to 60 min. The pH optimum was between 7.1 and 7.3. Bivalent cations (Mg2+ , Ca2+ ) and detergents inhibited the reaction. However, the same cell fractions as well as extracts of acetone-dried powder of brain from young or old rats possessed no enzyme activity for liberating the aldehyde from the acylated substrates: 1-[1-14 C]alk-1'-enyl-2-acyl- sn -glycero-3-phosphoethanolamine (plasmalogen) or plasmalogen of ox corpus callosum. 相似文献
52.
Summer distribution of Red-legged Partridges Alectoris rufa in relation to water availability on Mediterranean farmland 总被引:1,自引:0,他引:1
The suggestion that the summer distribution of Red-legged Partridges Alectoris rufa in the Mediterranean region is determined by the availability of surface water was examined on the agricultural farm, Alto Alentejo, southern Portugal. Partridge coveys were surveyed between 15 July and 15 August in 1993 and 1994. Using a vector-based Geographic Information System, we assessed, for each covey location and for the locations of a double number of random points, the distance to the nearest water point, distance to field boundaries, distance to water lines and land use classes. Univariate comparisons were made between the two groups of locations, and three multivariate logistic models were fitted through forward stepwise selection to the 1993, 1994 and pooled data sets to estimate the probability of sighting partridge coveys in the study area. Distance to water was significantly lower for partridge locations than for random points in both years and was the only variable selected for all logistic models. Apart from water availability, Red-legged Partridge locations were also affected by land use and distance to field boundaries. 相似文献
53.
M Vierbuchen J Gunawan H Debuch 《Hoppe-Seyler's Zeitschrift für physiologische Chemie》1979,360(8):1091-1097
The formation of 1-alkylglycerol from 1-alkyl-sn-glycero-3-phosphoethanolamine in different cell fractions of rat brain is reported. The substrates used were labelled either with 14C or 3H in the alkyl residue or with 14C in the alkyl and 3H in the ethanolamine residue. The examination of the lipid- and water-soluble cleavage products showed that both ethanolamine and phosphoethanolamine are liberated from the substrate in the microsomal fraction of 14-day-old rat brain. The latter product is rapidly hydrolyzed. In comparison with other cell fractions, the microsomes contained the highest enzyme activities, which exhibited a pH optimum of 7.1--7.5. SH-group reagents are inhibitors, whereas diisopropylfluorophosphate has no effect. As the animals age, these enzyme activities decrease in brain homogenates. 相似文献
54.
Background
Recent advances in molecular biology techniques provide an opportunity for developing detailed mathematical models of biological processes. An iterative scheme is introduced for model identification using available system knowledge and experimental measurements. 相似文献55.
Zea ribosomal repeat evolution and substitution patterns 总被引:2,自引:1,他引:1
Zea and Tripsacum nuclear ribosomal internal transcribed spacer (ITS)
sequences were used to evaluate patterns of concerted evolution, rates of
substitutions, patterns of methylation-induced deamination, and structural
constraints of the ITS. ITS pseudogenes were identified by their
phylogenetic position, differences in nucleotide composition, extensive
deamination at ancestral methylation sites, and substitutions resulting in
low-stability secondary RNA structures. Selection was important in shaping
the kinds of polymorphisms and substitutions observed in the ITS. ITS
substitution rates were significantly different among the Zea taxa.
Deamination of cytosines at methylation sites was a potent mutation source,
but selection appeared to maintain high methylation site density throughout
the ribosomal repeat except for the gene promoter. Nucleotide divergence
statistics identified selectively constrained regions at the 5' ends of the
ITS1 and ITS2.
相似文献
56.
57.
Concerted transpositions of mobile genetic elements coupled with fitness changes in Drosophila melanogaster 总被引:3,自引:0,他引:3
Pasyukova EG; Belyaeva ES; Kogan GL; Kaidanov LZ; Gvozdev VA 《Molecular biology and evolution》1986,3(4):299-312
In an inbred low-activity (LA) strain of Drosophila melanogaster with a low
level of fitness and a complex of inadaptive characters, in situ
hybridization reveals an invariant pattern of distribution of three
copia-like elements (mdg-1, mdg-3, and copia). Rare, spontaneous, multiple
transpositions of mobile elements in the LA strain were shown to be coupled
with a drastic increase of fitness. A changed pattern of various types of
mobile elements was also observed on selecting the LA strain for higher
fitness. High-fitness strains show transpositions of mobile elements to
definite chromosomal sites ("hot spots"). Concerted changes in the location
of three different mobile elements were found to be coupled with an
increase of fitness. The mdg-1 distribution patterns were also examined in
two low-fitness strains independently selected from the high-fitness ones.
Fitness decrease was accompanied by mdg-1 excision from the hot spots of
their location usually detected in the high-fitness strains. The results
suggest the existence of a system of adaptive transpositions of mobile
elements that takes part in fitness control.
相似文献
58.
59.
Talia Gershon Kasra Sardashti Oki Gunawan Ravin Mankad Saurabh Singh Yun Seog Lee John A. Ott Andrew Kummel Richard Haight 《Liver Transplantation》2016,6(22)
The kesterite material Cu2ZnSn(S,Se)4 (CZTSSe) is an attractive earth‐abundant semiconductor for photovoltaics. However, the power conversion efficiency is limited by a large density of I–II antisite defects, which cause severe band tailing and open‐circuit voltage loss. Ag2ZnSnSe4 (AZTSe) is a promising alternative to CZTSSe with a substantially lower I–II antisite defect density and smaller band tailing. AZTSe is weakly n‐type, and this study reports for the first time on how the carrier density is impacted by stoichiometry. This study presents the first‐ever photovoltaic device based on AZTSe, which exhibits an efficiency of 5.2%, which is the highest value reported for an n‐type thin‐film absorber. Due to the weakly n‐type nature of the absorber, a new architecture is employed (SnO:F/AZTSe/MoO3/ITO) to replace conventional contacts and buffer materials. Using this platform, it is shown that the band tailing parameter in AZTSe more closely resembles that of CIGSe than CZTSSe, underscoring the strong promise of this absorber. In demonstrating the ability to collect photogenerated carriers from AZTSe, this study paves the way for novel thin‐film heterojunction architectures where light absorption in the n‐type device layer can supplement absorption in the p‐type layer as opposed to producing a net optical loss. 相似文献
60.
Apomixis enables the clonal propagation of maternal genotypes through seed. If apomixis could be harnessed via genetic engineering or introgression, it would have a major economic impact for agricultural crops. In the grass species Pennisetum squamulatum and Cenchrus ciliaris (syn. P. ciliare), apomixis is controlled by a single dominant “locus”, the apospory-specific genomic region (ASGR). For P. squamulatum, 18 published sequenced characterized amplified region (SCAR) markers have been identified which always co-segregate with apospory. Six of these markers are conserved SCARs in the closely related species, C. ciliaris and co-segregate with the trait. A screen of progeny from a cross of sexual × apomictic C. ciliaris genotypes identified a plant, A8, retaining two of the six ASGR-linked SCAR markers. Additional and newly identified ASGR-linked markers were generated to help identify the extent of recombination within the ASGR. Based on analysis of missing markers, the A8 recombinant plant has lost a significant portion of the ASGR but continues to form aposporous embryo sacs. Seedlings produced from aposporous embryo sacs are 6× in ploidy level and hence the A8 recombinant does not express parthenogenesis. The recombinant A8 plant represents a step forward in reducing the complexity of the ASGR locus to determine the factor(s) required for aposporous embryo sac formation and documents the separation of expression of the two components of apomixis in C. ciliaris. 相似文献