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排序方式: 共有222条查询结果,搜索用时 15 毫秒
1.
Gerd Reuter Roland Schauer Claudia Szeiki Johannis P Kamerling Johannes FG Vliegenthart 《Glycoconjugate journal》1989,6(1):35-44
Periodate oxidation of terminalN-acetyl- andN-glycoloylneuraminic acid residues in the mucins from edible bird nest substance and pig submandibular gland, respectively, can be carried out under conditions which exclusively give rise to the formation of the C-7 analogues of these sialic acids. In contrast, the C-8 compounds can be obtained in a maximum yield of about 40%. Under identical conditions,N-glycoloylneuraminic acid is oxidized about 1.5 times faster than theN-acetylated derivative. After release of the sialic acids by acid hydrolysis, the characterization of the oxidation products was carried out by TLC, by GLC and GLC-MS of the corresponding pertrimethylsilyl derivatives, and by 500-MHz1H-NMR spectroscopy. In addition, molar response factors for GLC analysis and extinction coefficients in the orcinol/Fe3+/HCl assay were determined. 相似文献
2.
The out of hours workload of a training practice in a suburban and semirural area on the south coast of England was studied for one year. An overall rate of contact of 273/1000 patients was found, which indicated a workload greater than that reported in most other studies. The duty doctor received over 35 telephone calls from patients during some Saturdays (1200 Saturday to 0800 Sunday) and Sundays (0800 to 0800 Monday), up to five being between 2300 and 0700. Of the patients who contacted a general practitioner, 44% were given advice by telephone and 4.9% were admitted to hospital. The admission rate was lower than that given in other studies. A considerable proportion of the workload arose from doctors covering the casualty department of a cottage hospital. Patients having a high expectation of 24 hour care by general practitioners in an area of comparative affluence (Jarman indices -13.8 to 1.7) may account for this aspect of the workload. 相似文献
3.
Whitby LG 《Proceedings of the Royal Society of Medicine》1968,61(8):763-766
4.
Biological and molecular variability of human immunodeficiency virus type 2 isolates from The Gambia. 总被引:14,自引:9,他引:5 下载免费PDF全文
T F Schulz D Whitby J G Hoad T Corrah H Whittle R A Weiss 《Journal of virology》1990,64(10):5177-5182
Seven new human immunodeficiency virus type 2 (HIV-2) isolates (CBL-20 to CBL-26) from The Gambia were characterized. Their cytopathogenicity and growth in vitro correlated with the severity of clinical disease. CBL-22 was highly sensitive to neutralization by HIV-2 sera and was cross-neutralized by some HIV-1 sera. These findings, the differing sizes of envelope glycoproteins of individual isolates, and the sequence analysis of amplified regions of the viral DNAs show that these HIV-2 isolates from one geographical region in West Africa exhibit biological and genome variability comparable to that observed for HIV-1. 相似文献
5.
alpha 1-Proteinase inhibitor (alpha 1-PI), a member of the serine
proteinase inhibitor superfamily, has a primary role in controlling
neutrophil elastase activity within the mammalian circulation. Several
studies have indicated that the reactive center region of alpha 1-PI, the
amino acid sequence of which is critical to recognition of and binding to
target proteinases, is highly divergent within and among species. This
appears to be a consequence of accelerated rates of evolution that may have
been driven by positive Darwinian selection. In order to examine this and
other features of alpha 1-PI evolution in more detail, we have isolated and
sequenced cDNAs representing alpha 1- PI mRNAs of the mouse species Mus
saxicola and Mus minutoides and have compared these with a number of other
mammalian alpha 1-PI mRNAs. Relative to other mammalian mRNAs, the extent
of nonsynonymous substitution is generally high throughout the alpha 1-PI
mRNA molecule, indicating greater overall rates of amino acid substitution.
Within and among mouse species, the 5'-half of the mRNA, but not the
3'-half, has been homogenized by concerted evolution. Finally, the reactive
center is under diversifying or positive Darwinian selection in murid
rodents (rats, mice) and guinea pigs yet is under purifying selection in
primates and artiodactyls. The significance of these findings to alpha 1-PI
function and the possible selective forces driving evolution of serpins in
general are discussed.
相似文献
6.
Processing of intermediates in recombination and DNA repair: identification of a new endonuclease that specifically cleaves Holliday junctions. 总被引:12,自引:2,他引:10 下载免费PDF全文
The formation and subsequent resolution of Holliday junctions are critical stages in recombination. We describe a new Escherichia coli endonuclease that resolves Holliday intermediates by junction cleavage. The 14 kDa Rus protein binds DNA containing a synthetic four-way junction (X-DNA) and introduces symmetrical cuts in two strands to give nicked duplex products. Rus also processes Holliday intermediates made by RecA into products that are characteristic of junction resolution. The cleavage activity on X-DNA is remarkably similar to that of RuvC. Both proteins preferentially cut the same two strands at the same location. Increased expression of Rus suppresses the DNA repair and recombination defects of ruvA, ruvB and ruvC mutants. We conclude that all ruv strains are defective in junction cleavage, and discuss pathways for Holliday junction resolution by RuvAB, RuvC, RecG and Rus. 相似文献
7.
The SOS system of Escherichia coli aids survival following damage to DNA by promoting DNA repair while cell division is delayed. Induction of the SOS response is dependent on RecA and also on the product of recF. We show that normal induction also requires the products of recO and recR. SOS induction was monitored using a sfiA-lacZ fusion strain. Induction was delayed to a similar degree by mutation in recF, recO or recR. A similar effect was observed following overexpression of RecR from a recombinant recR
+plasmid. We show that the overexpression of RecR also reduces the UV resistance of a recBC sbcBC strain and of a sfiA strain, but not of a rec
+
sfiA
+strain. The implications of these data for the kinetics of DNA repair are discussed. 相似文献
8.
Characterization and crystallization of human uroporphyrinogen decarboxylase. 总被引:4,自引:0,他引:4 下载免费PDF全文
J. D. Phillips F. G. Whitby J. P. Kushner C. P. Hill 《Protein science : a publication of the Protein Society》1997,6(6):1343-1346
The cytosolic enzyme uroporphyrinogen decarboxylase (URO-D) catalyzes the fifth step in the heme biosynthetic pathway, converting uroporphyrinogen to coproporphyrinogen by decarboxylating the four acetate side chains of the substrate. Recombinant human URO-D has been expressed in Escherichia coli with a histidine tag and has been purified to homogeneity. Purified protein was determined to be a monodisperse dimer by dynamic light scattering. Equilibrium sedimentation analysis confirmed that the protein is dimeric, with a dissociation constant of 0.1 microM. URO-D containing an amino-terminal histidine tag was crystallized in space group P3(1)21 or its enantiomer P3(2)21 with unit cell dimensions a = b = 103.6 A, c = 75.2 A. There is one molecule in the asymmetric unit, consistent with generation of the dimer by the twofold axis of this crystallographic operator. Native data have been collected to 3.0 a resolution. 相似文献
9.
Wound healing in the fetus occurs rapidly, by a regenerative process and without an inflammatory response, resulting in complete restitution of normal tissue function. By contrast, in the adult, wounds heal with scar formation, which may impair function and inhibit further growth. The cellular mechanisms underlying these differing forms of wound healing are unknown but the extracellular matrix (ECM), through its effects on cell function, may play a key role. We have studied the ECM in upper lip wounds of adult, neonatal and fetal mice at days 14, 16 and 18 of gestation. The spatial and temporal distribution of collagen types I, III, IV, V and VI, fibronectin, tenascin, laminin, chondroitin and heparan sulphates were examined immunohistochemically. Results from the fetal groups were essentially similar whilst there were distinct differences between fetus, neonate and adult. Fibronectin was present at the surface of the wound in all groups at 1 h post-wounding. Tenascin was also present at the wound surface but the time at which it was first present differed between fetus (1 h), neonate (12 h) and adult (24 h). The time of first appearance paralleled the rate of wound healing which was most rapid in the fetus and slowest in the adult. Tenascin inhibits the cell adhesion effect of fibronectin and during development the appearance of tenascin correlates with the initiation of cell migration. During wound healing the appearance of tenascin preceded cell migration and the rapid closure of fetal wounds may be due to the early appearance of tenascin in the wound. Collagen types I, III, IV, V and VI were present in all three wound groups but the timing and pattern of collagen deposition differed, with restoration of the normal collagen pattern in the fetus and a scar pattern in the adult. This confirms that lack of scarring in fetal wounds is due to the organisation of collagen within the wound and not simply lack of collagen formation. The distribution of chondroitin sulphate differed between normal fetal and adult tissues and between fetal and adult wounds. Its presence in the fetal wound may alter collagen fibril formation. No inflammatory response was seen in the fetal wounds. The differences in the ECM of fetal and adult wounds suggests that it may be possible to alter the adult wound so that it heals by a fetal-like process without scar formation, loss of tissue function or restriction of growth. 相似文献
10.