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241.
242.
Nicotinic acid has functional groups capable of forming complexes with trace metals. The present study examines the effect of nicotinic acid supplementation on absorption and utilization of zinc and iron. In vitro zinc uptake by human erythrocytes was studied using blood samples of 10 healthy subjects. It was found that 8 moles nicotinic acid or NADP increased 65Zn uptake by 38.9% and 43.1% in fasting, and by 70.9% and 28.1% in postprandial conditions. In animal experiments, nicotinic acid supplementation to finger millet based diet resulted in significant enhancement of percent zinc absorption, liver zinc and growth of weanling mice (P < 0.05). When mice were fed with nicotinic acid-deficient, -adequate and -excess synthetic diets for four weeks it was observed that, in comparison with the nicotinic acid-deficient diet, percent zinc absorption, intestinal zinc, percent haeomoglobin and liver iron increased significantly under nicotinic acid-adequate and -excess conditions. The results obtained suggested that nicotinic acid, in addition to its known effect on growth and metabolism, may be playing an important role in enhancing zinc and iron utilization. 相似文献
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244.
Evolution of the secondary structures and compensatory mutations of the ribosomal RNAs of Drosophila melanogaster 总被引:10,自引:0,他引:10
This paper examines the effects of DNA sequence evolution on RNA secondary
structures and compensatory mutations. Models of the secondary structures
of Drosophila melanogaster 18S ribosomal RNA (rRNA) and of the complex
between 2S, 5.8S, and 28S rRNAs have been drawn on the basis of comparative
and energetic criteria. The overall AU richness of the D. melanogaster
rRNAs allows the resolution of some ambiguities in the structures of both
large rRNAs. Comparison of the sequence of expansion segment V2 in D.
melanogaster 18S rRNA with the same region in three other Drosophila
species and the tsetse fly (Glossina morsitans morsitans) allows us to
distinguish between two models for the secondary structure of this region.
The secondary structures of the expansion segments of D. melanogaster 28S
rRNA conform to a general pattern for all eukaryotes, despite having highly
divergent sequences between D. melanogaster and vertebrates. The 70 novel
compensatory mutations identified in the 28S rRNA show a strong (70%) bias
toward A-U base pairs, suggesting that a process of biased mutation and/or
biased fixation of A and T point mutations or AT-rich slippage-generated
motifs has occurred during the evolution of D. melanogaster rDNA. This
process has not occurred throughout the D. melanogaster genome. The
processes by which compensatory pairs of mutations are generated and spread
are discussed, and a model is suggested by which a second mutation is more
likely to occur in a unit with a first mutation as such a unit begins to
spread through the family and concomitantly through the population.
Alternatively, mechanisms of proofreading in stem-loop structures at the
DNA level, or between RNA and DNA, might be involved. The apparent
tolerance of noncompensatory mutations in some stems which are otherwise
strongly supported by comparative criteria within D. melanogaster 28S rRNA
must be borne in mind when compensatory mutations are used as a criterion
in secondary-structure modeling. Noncompensatory mutation may extend to the
production of unstable structures where a stem is stabilized by RNA-
protein or additional RNA-RNA interactions in the mature ribosome. Of
motifs suggested to be involved in rRNA processing, one (CGAAAG) is
strongly overrepresented in the 28S rRNA sequence. The data are discussed
both in the context of the forces involved with the evolution of multigene
families and in the context of molecular coevolution in the rDNA family in
particular.
相似文献
245.
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247.
Adam R Burns W Zac Stephens Keaton Stagaman Sandi Wong John F Rawls Karen Guillemin Brendan JM Bohannan 《The ISME journal》2016,10(3):655-664
Despite their importance to host health and development, the communities of microorganisms associated with humans and other animals are characterized by a large degree of unexplained variation across individual hosts. The processes that drive such inter-individual variation are not well understood. To address this, we surveyed the microbial communities associated with the intestine of the zebrafish, Danio rerio, over developmental time. We compared our observations of community composition and distribution across hosts with that predicted by a neutral assembly model, which assumes that community assembly is driven solely by chance and dispersal. We found that as hosts develop from larvae to adults, the fit of the model to observed microbial distributions decreases, suggesting that the relative importance of non-neutral processes, such as microbe-microbe interactions, active dispersal, or selection by the host, increases as hosts mature. We also observed that taxa which depart in their distributions from the neutral prediction form ecologically distinct sub-groups, which are phylogenetically clustered with respect to the full metacommunity. These results demonstrate that neutral processes are sufficient to generate substantial variation in microbiota composition across individual hosts, and suggest that potentially unique or important taxa may be identified by their divergence from neutral distributions. 相似文献
248.
We sampled populations of forest-floor dwelling cave and ground wētā using footprint tracking tunnels and spotlight transect counts in southern beech forest, New Zealand. Samples were compared to estimates of wētā density based on mark–recapture estimates from 25?m2 enclosures. Both activity indices captured variability in cave wētā in time and space, were strongly correlated with each other, and have the potential for monitoring cave wētā activity levels. Comparisons between indices and cave wētā density estimates were equivocal, as recapture rates were too low to calculate high-resolution density estimates. We also found that cave wētā counts had a curved relationship increasing with temperature, and a negative relationship with increasing shrub and woody debris cover. Based on these preliminary results, tracking tunnels could be a viable method of monitoring cave wētā as they appear more efficient than transect counts and are relatively inexpensive. However, further calibration trials are needed to determine if indices mirror robust population density estimates. 相似文献
249.
250.
Heterologous expression of an engineered truncated form of human Lewis fucosyltransferase (Fuc-TIII) by the methylotrophic yeast Pichia pastoris 总被引:1,自引:0,他引:1
Gallet PF; Vaujour H; Petit JM; Maftah A; Oulmouden A; Oriol R; Le Narvor C; Guilloton M; Julien R 《Glycobiology》1998,8(9):919-925
A stable GS115 Pichia pastoris recombinant strain was constructed to
secrete a truncated form of the human alpha(1,3/4) fucosyltransferase
(amino acids 45-361). Enzyme production resulted from a secretory pathway
based on the pre-pro- alpha mating factor signal sequence of the yeast
Saccharomyces cerevisiae . Following its transit through the Golgi
apparatus, the enzyme accumulated in the periplasmic space before its
release in the culture broth (about 30 mg/l). Cell-enclosed enzyme (
approximately 0.16%) proved to be fairly stable for many freezing and
thawing cycles and could be used several times as an immobilized catalyst.
Soluble enzyme (>99.8%) representing the main protein of the culture
broth (10%) has been characterized by Western-blotting, substrate
specificities and kinetic parameters. The two forms (cell- enclosed and
soluble) of recombinant enzyme may be used for in vitro synthesis of
Lewisadeterminants.
相似文献