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61.
62.
目的:磷酸钙骨水泥(Calcium phosphate cement,CPC)以其诸多优点正得到了越来越多的应用,但其较差的力学性能表现也限制了它的使用范围。本研究目的在于改善磷酸钙骨水泥的力学性能,同时评估改性后的磷酸钙骨水泥的其他性能。方法:通过丝素蛋白(Silk fibroin,SF)的矿化自组装方法制备丝素蛋白/羟基磷灰石复合物(silk fibroin/hydroxyapitite composite, SF/HA)。按照1%、2%、3%、4%的质量分数加入磷酸钙骨水泥中,与磷酸钙骨水泥组对比。比较内容包括力学强度、抗渍散性能及细胞毒性。结果:以丝素蛋白溶液为液相组的磷酸钙骨水泥强度大约为35MPa。随后随着添加丝素蛋白/羟基磷灰石复合物的质量分数从1%增至3%,磷酸钙骨水泥的强度逐渐增加(P〈0.05),最高约至45MPa。而当丝素蛋白/羟基磷灰石的质量分数达到4%时,磷酸钙骨水泥的强度较质量分数3%组小幅度下降至43MPa(P〈0.05)。以丝素蛋白溶液作为液相时,磷酸钙骨水泥的抗溃散能力也得到了加强。在MTT法测定细胞活力的对照实验中,无论是加入丝素蛋白溶液或丝素蛋白/羟基磷灰石复合物,都未观察到细胞毒性。结论:在磷酸钙骨水泥中加入3%质量分数的丝素蛋白/羟基磷灰石复合物,能显著提高磷酸钙骨水泥的抗压强度。而丝素蛋白溶液作为液相可改善磷酸钙骨水泥的抗溃散能力。同时,丝素蛋白和丝素蛋白/羟基磷灰石复合物都不表现出细胞毒性。更理想的力学强度和更强的抗溃散能力,大大扩展了磷酸钙骨水泥的应用范围。 相似文献
63.
Two soluble glycosyltransferases glycosylate less efficiently in vivo than their membrane bound counterparts 总被引:2,自引:1,他引:1
Zhu G; Allende ML; Jaskiewicz E; Qian R; Darling DS; Worth CA; Colley KJ; Young WW Jr 《Glycobiology》1998,8(8):831-840
Many Golgi glycosyltransferases are type II membrane proteins which are
cleaved to produce soluble forms that are released from cells. Cho and
Cummings recently reported that a soluble form of alpha1, 3-
galactosyltransferase was comparable to its membrane bound counterpart in
its ability to galactosylate newly synthesized glycoproteins (Cho,S.K. and
Cummings,R.D. (1997) J. Biol. Chem., 272, 13622-13628). To test the
generality of their findings, we compared the activities of the full length
and soluble forms of two such glycosyltransferases, ss1,4
N-Acetylgalactosaminyltransferase (GM2/GD2/ GA2 synthase; GalNAcT) and beta
galactoside alpha2,6 sialyltransferase (alpha2,6-ST; ST6Gal I), for
production of their glycoconjugate products in vivo . Unlike the full
length form of GalNAcT which produced ganglioside GM2 in transfected cells,
soluble GalNAcT did not produce detectable GM2 in vivo even though it
possessed in vitro GalNAcT activity comparable to that of full length
GalNAcT. When compared with cells expressing full length alpha2,6-ST, cells
expressing a soluble form of alpha2,6-ST contained 3-fold higher
alpha2,6-ST mRNA levels and secreted 7-fold greater alpha2,6-ST activity as
measured in vitro , but in striking contrast contained 2- to 4-fold less of
the alpha2,6-linked sialic acid moiety in cellular glycoproteins in vivo .
In summary these results suggest that unlike alpha1,3-galactosyltransferase
the soluble forms of these two glycosyltransferases are less efficient at
glycosylation of membrane proteins and lipids in vivo than their membrane
bound counterparts.
相似文献
64.
CA Istock JA Bell N Ferguson NL Istock 《Journal of industrial microbiology & biotechnology》1996,17(3-4):137-150
A discussion of the species problem in modern evolutionary biology serves as the point of departure for an exploration of how the basic science aspects of this problem relate to efforts to map bacterial diversity for practical pursuits—for prospecting among the bacteria for useful genes and gene-products. Out of a confusing array of species concepts, the Cohesion Species Concept seems the most appropriate and useful for analyzing bacterial diversity. Techniques of allozyme analysis and DNA fingerprinting can be used to put this concept into practice to map bacterial genetic diversity, though the concept requires minor modification to encompass cases of complete asexuality. Examples from studies of phenetically definedBacillus species provide very partial maps of genetic population structure. A major conclusion is that such maps frequently reveal deep genetic subdivision within the phenetically defined specles; divisions that in some cases are clearly distinct genetic species. Knowledge of such subdivisions is bound to make prospecting within bacterial diversity more effective. Under the general concept of genetic cohesion a hypothetical framework for thinking about the full range of species conditions that might exist among bacteria is developed and the consequences of each such model for species delineation, and species identification are discussed. Modes of bacterial evolution, and a theory of bacterial speciation with and without genetic recombination, are examined. The essay concludes with thoughts about prospects for very extensive mapping of bacterial diversity in the service of future efforts to find useful products. In this context, evolutionary biology becomes the handmaiden of important industrial activities. A few examples of past success in commercializing bacterial gene-products from species ofBacillus and a few other bacteria are reviewed. 相似文献
65.
Lysosomal enzyme oligosaccharide phosphorylation in mouse lymphoma cells: specificity and kinetics of binding to the mannose 6-phosphate receptor in vivo 总被引:12,自引:10,他引:2 下载免费PDF全文
Phosphomannosyl residues on lysosomal enzymes serve as an essential component of the recognition marker necessary for binding to the mannose 6-phosphate (Man 6-P) receptor and translocation to lysosomes. The high mannose-type oligosaccharide units of lysosomal enzymes are phosphorylated by the following mechanism: N-acetylglucosamine 1-phosphate is transferred to the 6 position of a mannose residue to form a phosphodiester; then N- acetylglucosamine is removed to expose a phosphomonoester. We examined the kinetics of this phosphorylation pathway in the murine lymphoma BW5147.3 cell line to determine the state of oligosaccharide phosphorylation at the time the newly synthesized lysosomal enzymes bind to the receptor. Cells were labeled with [2-(3)H]mannose for 20 min and then chased for various times up to 4 h. The binding of newly synthesized glycoproteins to the Man 6-P receptor was followed by eluting the bound ligand with Man 6-P. Receptor-bound material was first detected at 30 min of chase and reached a maximum at 60 min of chase, at which time approximately 10 percent of the total phosphorylated oligosaccharides were associated with the receptor. During longer chase times, the total quantity of cellular phosphorylated oligosaccharides decreased with a half-time of 1.4 h, suggesting that the lysosomal enzymes had reached their destination and had been dephosphorylated. The structures of the phosphorylated aligosaccharides of the eluted ligand were then determined and compared with the phosphorylated oligosaccharides of molecules which were not bond to the receptor. The major phosphorylated oligosaccharide species present in the nonreceptor-bound material contained a single phosphosphodiester at all time examined. In contrast, receptor-bound oligosaccharides were greatly enriched in species possessing one and two phosphomonoesters. These results indicate that binding of newly synthesized lysosomal enzymes to the Man 6-P receptor occurs only after removal of the covering N- acetylglucosamine residues. 相似文献
66.
67.
Klausmeier CA 《The American naturalist》1998,152(2):303-310
68.
Tempo and mode of concerted evolution in the L1 repeat family of mice 总被引:10,自引:0,他引:10
Martin SL; Voliva CF; Hardies SC; Edgell MH; Hutchison CA d 《Molecular biology and evolution》1985,2(2):127-140
A 300-bp DNA sequence has been determined for 30 (10 from each of three
species of mice) random isolates of a subset of the long interspersed
repeat family L1. From these data we conclude that members of the L1 family
are evolving in concert at the DNA sequence level in Mus domesticus, Mus
caroli, and Mus platythrix. The mechanism responsible for this phenomenon
may be either duplicative transposition, gene conversion, or a combination
of the two. The amount of intraspecies divergence averages 4.4%, although
between species base substitutions accumulate at the rate of approximately
0.85%/Myr to a maximum divergence of 9.1% between M. platythrix and both M.
domesticus and M. caroli. Parsimony analysis reveals that the M. platythrix
L1 family has evolved into a distinct clade in the 10-12 Myr since M.
platythrix last shared a common ancestor with M. domesticus and M. caroli.
The parsimony tree also provides a means to derive the average half-life of
L1 sequences in the genome. The rates of gain and loss of individual copies
of L1 were estimated to be approximately equal, such that approximately
one-half of them turn over every 3.3 Myr.
相似文献
69.
Hierarchical folding and reorganization of chromosomes are linked to transcriptional changes in cellular differentiation 下载免费PDF全文
Mariano Barbieri Benjamin L Moore Dorothee CA Kraemer Stuart Aitken Sheila Q Xie Kelly J Morris Masayoshi Itoh Hideya Kawaji Ines Jaeger Yoshihide Hayashizaki Piero Carninci Alistair RR Forrest The FANTOM Consortium Colin A Semple Josée Dostie Ana Pombo Mario Nicodemi 《Molecular systems biology》2015,11(12)
70.
Carl?Shooner Pierre-Luc?Caron Guylaine?Fréchette-Frigon Valérie?Leblanc Marie-Claude?Déry Eric?AsselinEmail author 《Reproductive biology and endocrinology : RB&E》2005,3(1):20