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131.
132.
Stress relaxation experiments were performed on specimens from a human intervertebral disc. Specimens were made from the nucleus pulposus and from the external lamellae of the anulus fibrosus in two different orientations. Tests were run with varying moisture content so as to develop a relaxation master curve. A model was developed based on the experimental data. It was found that the short term master curve for the lamellae of the anulus and nucleus are similar, whereas the long term rubbery plateau is different between the lamellae and the nucleus. It was also established that the master curves for different lamellae and the nucleus were shifted relative to each other in the time domain due to changes in water content. The average relaxation modulus of the whole disc was obtained by averaging the properties between the anulus and nucleus. This model was then used for studies of Schmorl's nodes, of degenerated discs and for circumstances in which hydration is considered to be important. 相似文献
133.
MHT Hipondoka BCW van der Waal MH Ndeutapo L Hango 《African Journal of Aquatic Science》2018,43(3):199-214
The triangle between the Kavango and Kunene rivers is drained by the Cuvelai, an ephemeral and deltaic drainage system covering more than 100 000 km2. In good rainfall years, the area becomes populated by fish communities dominated by five species migrating southward towards the endorheic Etosha Pan, the basin’s terminal sump. When water dries up, fish subsequently die-off and their sudden appearance in rainy years has captivated scientists for decades. The current study was prompted by hitherto untapped indigenous knowledge through narratives of opportunistic fish harvesting of migrating fish at temporary connections between the Kunene River and the Cuvelai- Etosha Basin. A reconnaissance fish survey in 2017 was complemented by digital satellite images and elevation data analyses. Results support the presence of at least three major ephemeral fish migration routes. The dominant fish genera migrating upstream in Kunene tributaries comprise Enteromius, Oreochromis and Clarias, all eurytopic and known to undertake upstream, lateral and downstream migrations on floodplains. Although other notable fish refugia in the Cuvelai–Etosha Basin are yet to be identified, there is a necessity for the protection and management of these migration routes in tandem with studies on the nature and extent of this inter-basin fish migration under climate change and variability. 相似文献
134.
The hamster gene for uridine diphosphate N-acetyl-D-glucosamine:dolichyl phosphate N-acetylglucosaminyl phosphoryl transferase(L-G1PT) was found to extend over 6.5 kb and to contain nineexons. The exons ranged in size from 63 to 214 bp, encodingthe 408 amino acid protein. The introns ranged from 85 bp to1.4 kb. Upstream 5' sequences included two possible TATA boxes,one possible CCAAT box and at least two potential GC boxes.Heterologous expression was successful in Schizosaccharomycespombe, and resulted in cells that were tunicamycin resistantand had 12-fold more L-G1PT activity than wild-type cells. Antiserumprepared to a hydrophilic peptide (residues 300320) ofthe L-G1PT protein reacted with a 3536 kDa protein inmembrane samples from Chinese hamster ovary (CHO) cells andS.pombe cells that had increased levels of L-G1PT activity.In both cases, antigenic peptide competed with the 3536kDa protein detected by the antiserum. N-acetylglucosarmine 1-phosphate transferase dolichol glycosylation 相似文献
135.
The molecular organization of the beta-globin complex of the deer mouse, Peromyscus maniculatus 总被引:1,自引:0,他引:1
Padgett RW; Loeb DD; Snyder LR; Edgell MH; Hutchison CA d 《Molecular biology and evolution》1987,4(1):30-45
Recombinant DNA clones have been isolated that contain 80 kb of the
beta-globin complex from the deer mouse, Peromyscus maniculatus.
Comparisons of this complex with that from the laboratory mouse, Mus
domesticus (with an order 5'-Hbby, Hbb-bhO, Hbb-bhl, Hbb-bh2, Hbb-bh3,
Hbb-bl, Hbb-b2 3') highlight organizational trends in the beta-globin
complex since the two species diverged. Unlike other mammals studied thus
far, the deer mouse possesses three adult genes. Partial sequence analysis
indicates that each of the three adult genes is intact and hence may be
functional. Hybridization of one of the two Mus pseudogenes, Hbb-bh3, to
genomic blots from Peromyscus reveals that it has a homologous counterpart
in Peromyscus. Homologous genes to the two gamma-like Mus genes, Hbb-bhO
and Hbb-bhl, are also found in Peromyscus. The strong hybridization between
the Hbb-bhl genes and significant nucleotide similarity between the Hbb-bhO
genes suggest that both pairs are important for the ontogeny of these mice
although no known product has been identified for the Hbb-bhO genes. The
presence of Hbb-bhO and Hbb-bhl in Peromyscus suggests that the duplication
that created this related gene set occurred before the two lineages
diverged. A single gene for Hbb-y has been isolated from Peromyscus. The
adult region in Peromyscus has undergone significant divergence from the
same region in Mus, having three rather than two adult genes, the
acquisition of at least 15 kb of extra DNA relative to Mus, and possibly
the loss of the Hbb-bh2 pseudogene. The nonadult region of the complex, in
contrast, contains the same set of genes apparently distributed over the
same amount of DNA as in the Mus beta- globin complex. This observation
suggests that the embryonic region of the complex is more evolutionarily
stable than the adult region.
相似文献
136.
137.
A key step in the assembly of oligosaccharide-lipid intermediatesin N-linked glycosylation is the transfer of N-acetylglucosamine1-phosphate to dolichyl phosphate, catalyzed by the enzyme UDP-N-acetylglucosaminyl:dolichylphosphate N-acetylglucosaminyl phosphoryl transferase (L-G1PT).Comparison of the amino acid sequences of L-G1PT from five diversespecies showed 75 amino acids identical in all five proteins.Using site-directed mutagen-esis, we analyzed the importanceof a number of these conserved residues to the enzymatic activityof L-G1PT using a plasmid shuffling procedure in Schizosaccharomycespombe. S.pombe cells containing a chromosomal deletion of theessential gpt+ gene are rescued by a plasmid containing theS.pombe gpt open reading frame. Replacement of that plasmidby a plasmid encoding a mutated hamster L-G1PT cDNA sequenceindicated that the mutated protein provided sufficient enzymeactivity to permit cell growth. Mutations of aspartic acid 252and asparagine 185 did not allow plasmid shuffling, indicatingthese residues were essential for activity. A combination ofmutations at asparagine 182 and tryptophan 122 did not allowplasmid shuffling, although the single mutations did. Overexpressionof the mutant proteins in S.pombe conferred tunicamycin (TM)resistance, indicating that the mutant proteins had a conformationnecessary for binding TM, a substrate analog. The mutant proteinswere also detected in Western blots and were correctly localizedto the membrane fractions. However, the overexpressed proteinsdid not increase the endogenous level of enzymatic activityin these cells, indicating they were enzymatically inactive. N-acetylglucosaminylphosphate transferase mutagenesis plasmid shuffling Schizosaccharomyces pombe tunicamycin 相似文献