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排序方式: 共有386条查询结果,搜索用时 31 毫秒
71.
72.
alpha-Tocopherol and protein kinase C inhibition enhance platelet-derived nitric oxide release. 总被引:7,自引:0,他引:7
Platelet activation is tightly regulated by products of the endothelium and platelets including nitric oxide (NO). Excess vascular oxidative stress has been associated with impaired NO release, and antioxidant status has been shown to alter endothelium-derived NO bioactivity. Although physiological levels of a-tocopherol are known to inhibit platelet function, the effect of a-tocopherol on platelet NO release is unknown. Loading platelets with physiologic levels of a-tocopherol increased platelet NO production approximately 1.5-fold (Pa-tocopherol, platelet NO release increased 50% (Pa-Tocopherol-loaded platelets also produced 74% less superoxide as compared with control (Pa-tocopherol inhibited PKC-dependent eNOS phosphorylation as determined by immunoprecipitation. Lastly, platelets isolated from NOS3-deficient mice released 80% less superoxide as compared with control animals (P=0.011), and incubation of NOS III-deficient platelets with 500 mM a-tocopherol only caused a modest additional decrease in platelet superoxide release (NS). Thus, a-tocopherol appears to enhance platelet NO release both in vitro and in vivo through antioxidant- and PKC-dependent mechanisms. 相似文献
73.
M A Noordermeer A J Van Dijken S C Smeekens G A Veldink J F Vliegenthart 《European journal of biochemistry》2000,267(9):2473-2482
Three full-length cDNAs from alfalfa seedlings coding for hydroperoxide lyases were cloned and expressed in Escherichia coli and characterized as cytochrome P450 enzymes. The isoenzymes were specific for 13-hydroperoxy linoleic and linolenic acids and did not use the 9-hydroperoxy isomers as substrates. Because alfalfa contains both specificities, this indicates the presence of two different types of hydroperoxide lyases, each specific for one kind of substrate. The enzymes contain 480 amino acids (54 kDa) and contain an unusual, nonplastidic N-terminal sequence of 22 amino acids, which strongly reduces the enzyme activity. The only known presequence of a hydroperoxide lyase (from Arabidopsis thaliana) was considered to be a transit sequence. The reduced enzyme activity, however, indicates that the hydroperoxide lyases with N-terminal extensions could be pro-enzymes. This hypothesis is supported by the fast release of hydroperoxide lyase products by plants upon wounding. One of the isoenzymes showed a strongly decreased Vmax and Km compared to the other two. Because this is probably due to the substitution of Ser377 by Phe; the residue at position 377 seems to be important. This is the first time that sufficient quantities of hydroperoxide lyase have been obtained for characterization studies, by circumventing difficult purification procedures and degradation of the enzyme. The high expression level, easy purification, good stability and high specificity make these cloned hydroperoxide lyases excellent tools to study the reaction mechanism and structure. We postulate an integrated reaction mechanism, based on the known chemistry of cytochrome P450 enzymes. This is the first mechanism that unifies all observed features of hydroperoxide lyases. 相似文献
74.
A P Corfield R Schauer L Dorland J F Vliegenthart H Wiegandt 《Journal of biochemistry》1985,97(2):449-461
Investigation of the action of highly purified Clostridium perfringens sialidase on ganglioside II3Neu5Ac-Gg4Cer and its oligosaccharide II3Neu5Ac-Gg4, in the presence and absence of sodium cholate, extend earlier results obtained with impure enzyme fractions. Sialidase labeled with 125I was found to bind to various ganglioside substrate micelles, including II3Neu5Ac-Gg4Cer, and to mixed ganglioside-sodium cholate micelles. No binding occurred between the enzyme and the ganglioside-derived oligosaccharide II3Neu5Ac-Gg4, even when radioactive II3Neu5Ac-Gg4-[3H]ol was used. The binding of sialidase to micellar substrate is a condition for enzymic hydrolysis. Correspondingly, II3Neu5Ac-Gg4Cer and II3Neu5Ac-Gg4Cer-sodium cholate micelles were hydrolyzed by the enzyme but II3Neu5Ac-Gg4 was not. Ganglioside oligosaccharide analogues containing an amino function at the reducing terminus or between two oligosaccharide chains, II3Neu5Ac-Gg4-NH2 and (II3Neu5Ac-Gg4)2NH, were hydrolyzed in the absence of cholate. A synthetic analogue of II3Neu5Ac-Gg4Cer containing only the fatty acid moiety and not the sphingosine residue (I1-deoxy-I1-stearamido-II3-monosialo-gangliotetraitol ) behaved as the ganglioside in the presence and absence of sodium cholate. 相似文献
75.
76.
K Sugahara Y Ohi T Harada P de Waard J F Vliegenthart 《The Journal of biological chemistry》1992,267(9):6027-6035
Shark cartilage proteoglycans bear predominantly chondroitin 6-sulfate. After exhaustive protease digestion, reductive beta-elimination, and subsequent chondroitinase ABC digestion, 13 hexasaccharide alditols, which are nonsulfated, sulfated, and/or phosphorylated, were obtained from the carbohydrate-protein linkage region. Six compounds, containing 0 or 1 sulfate and/or phosphate residue, represent approximately 40% of the isolated linkage hexasaccharide alditols. They were analyzed by chondroitinase ACII or alkaline phosphatase digestion in conjunction with high performance liquid chromatography, and by 500 MHz one- and two-dimensional 1H NMR spectroscopy. All six compounds have the conventional structure in common. Delta 4,5-GlcA beta 1-3GalNAc beta 1-4GlcA beta 1-3Gal beta 1-3Gal beta 1-4Xyl-ol One compound has no sulfate nor phosphate. Two of the monosulfated compounds have a O-sulfate on C-6 or on C-4 of the GalNAc residue. The third monosulfated compound has a novel O-sulfate on C-6 of the Gal residue attached to xylitol. The two phosphorylated compounds have O-phosphate on C-2 of Xyl-ol, and one of them has in addition sulfate on C-6 of GalNAc. 相似文献
77.
Improved purification of 12-lipoxygenase from rat basophilic leukemia cells and conditions for optimal enzyme activity 总被引:1,自引:0,他引:1
E M Van der Donk G R Dubois J Verhagen G A Veldink J F Vliegenthart 《Biochimica et biophysica acta》1991,1074(3):443-447
12-Lipoxygenase from rat basophilic leukemia cells was purified about 300-fold by protein-HPLC in a single run. Maximal 12-lipoxygenase activity was observed at pH 7.5, while the enzyme became almost inactive at pH 6 and 9. Although Ca2+ was not essential for 12-lipoxygenase activity, the partially purified enzyme was stimulated approx. 2-fold in the presence of 0.1-5.0 mM Ca2+. Contrary to 5-lipoxygenase from RBL-1 cells, 12-lipoxygenase was not inactivated by preincubation with Ca2+ for 1-10 min, nor was it stimulated by 0.1-10 mM ATP. 相似文献
78.
The "heptasaccharides" O-alpha-D-galactopyranosyl-(1----3)- O-alpha-D-glucopyranosyl-(1----3)-alpha, beta-L-rhamnopyranose 2'-[O-alpha-D-galactopyranosyl-(1----3)-O-alpha-D-glucopyranosyl- (1----3)-O-alpha-L-rhamnopyranosyl-(1----3)-D-ribit-5-yl sodium phosphate] (25) and O-alpha-D-galactopyranosyl- (1----3)-O-alpha-D-glucopyranosyl-(1----3)-alpha, beta-L-rhamnopyranose 2'-[O-alpha-D-galactopyranosyl-(1----3)-O-alpha-D-glucopyranosyl- (1----3)-O-alpha-L-rhamnopyranosyl-(1----4)-D-ribit-5-yl sodium phosphate] (27), which are structural elements of the capsular polysaccharides of Streptococcus pneumoniae types 6A and 6B ([----2)- -alpha-D-Galp-(1----3)-alpha-D-Glcp-(1----3)-alpha-L-Rhap- (1----X)-D-RibOH-(5-P----]n; 6A X = 3, 6B X = 4), respectively, have been synthesized. 2,4-Di-O-acetyl- 3-O-[2,4,6-tri-O-acetyl-3-O-(2,3,4,6-tetra-O-acetyl-alpha-D- galactopyranosyl)-alpha-D-glucopyranosyl]-alpha-L-rhamnopyranosyl trichloroacetimidate (13) was coupled with 5-O-allyloxycarbonyl-1,2,4-tri-O- benzyl-D-ribitol (10), using trimethylsilyl triflate as a promotor (----14), and deallyloxycarbonylation (----15) and conversion into the corresponding triethylammonium phosphonate then gave 16. Condensation of 16 with 4-methoxybenzyl 2,4-di-O-benzyl-3-O-[2,4,6-tri-O-benzyl-3-O-(3,4,6-tri-O-benzyl-alpha-D- galactopyranosyl)-alpha-D-glucopyranosyl]- alpha-L-rhamnopyranoside (22) followed by oxidation and deprotection afforded 25. 5-O-Allyl-1-O-allyloxycarbonyl-2,3-di-O-benzyl-D-ribitol (12) was coupled with 13, using trimethylsilyl triflate as a promoter, the resulting tetrasaccharide-alditol derivative 17 was deallyloxycarbonylated (----18), acetylated (----19), and deallylated (----20), and the product was converted into the triethylammonium phosphonate derivative 21. Condensation of 21 with 22 followed by oxidation and deprotection afforded 27. 相似文献
79.
Herman Van Halbeek Johannes F G Vliegenthart Hitoo Iwase Suchen Li Yu-Teh Li 《Glycoconjugate journal》1985,2(3-4):235-253
Dansyl glyco-asparagines were prepared from a partially fractionated mixture of hen egg white glycoproteins. Reverse-phase high performance liquid chromatography (HPLC) on a silica-based octadecyl column yielded ten such derivatives in a virtually pure state. The detailed structures of the glyco-asparagines were identified by 500-MHz1H nuclear magnetic resonance (NMR) spectroscopy. Two of them were found to be of the oligomannosideN-type, four were of the intersected-hybridN-type and another four were of the intersected multi-antennaryN-type. In monogalactosylated, intersected structures the galactose residue was proved by1H-NMR to be attached in (1–4)-linkage to the GlcNAc1-4Man1–3 branch.Dansyl glyco-asparagines turned out to be suitable derivatives for1H-NMR spectroscopic analysis. The combination of HPLC and high-resolution NMR spectroscopy of such derivatives proved to be a powerful technique in studying the (micro-)heterogeneity of sugar chains in glycoproteins.Abbreviations dns
dansyl (5-dimethylaminonaphthalene-1-sulfonyl)
- ODS
octadecyl-silica
- WEFT
water-eliminating Fourier transform
- DSS
sodium 4,4-dimethyl-4-silapentane-1-sulfonate
- OVA
ovalbumin
- OVM
ovomucoid
- OVT
ovotransferrin 相似文献
80.
Sophia A M Korrel Kenneth J Clemetson Herman Van Halbeek Johannis P Kamerling Jan J Sixma Johannes F G Vliegenthart 《Glycoconjugate journal》1985,2(3-4):229-234
The hydrazinolysis procedure currently used for the release ofN-glycosidic carbohydrate chains was applied to glycocalicin. The resulting mixture of oligosaccharide-alditols was fractionated by high-voltage paper electrophoresis into a neutral (5%) and several acidic fractions. The neutral compounds were passed over Bio-Gel P-4. SomeN-glycosidic oligosaccharide-alditols, of theN-acetyllactosamine type as well as of the oligomannoside type, were found to be present. However, oligosaccharide-alditols derived fromO-glycosidic carbohydrate chains were also found, indicating a partial cleavage of GalNAc1-OSer/Thr linkages under the hydrazinolysis conditions applied. One of the neutralO-glycosidic components was characterized, by 500-MHz1H-NMR spectroscopy in combination with sugar analysis, as the following pentasaccharidealditol:
In addition the afuco analogue of this compound was obtained. 相似文献