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101.
Cytochrome P-450-Dependent omega-Hydroxylation of Lauric Acid by Microsomes from Pea Seedlings
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Microsomes from apical buds of pea (Pisum sativum L. var. Téléphone à rames) seedlings hydroxylate lauric acid at the ω-position. This oxidation is catalyzed by a cytochrome P-450 enzyme which differs from laurate hydroxylases previously described in microorganisms and mammals by its strict substrate specificity and the ability of low NADH concentrations to support unusually high oxidation rates. The apparent Km for lauric acid was 20 micromolar. NADPH- and NADH-dependent laurate hydroxylation followed non-Michaelian kinetics with apparent Km values ranging from 0.2 to 28 micromolar for NADPH, and 0.2 to 318 micromolar for NADH. When induced by the photomorphogenic photoreceptor phytochrome, the time course for the enhancement of laurate ω-hydroxylase was totally different from that of the cinnamic acid 4-hydroxylase, providing evidence for the existence of multiple cytochrome P-450 species in pea microsomes. 相似文献
102.
F Pinot J P Salaün H Bosch A Lesot C Mioskowski F Durst 《Biochemical and biophysical research communications》1992,184(1):183-193
A microsomal fraction from etiolated Vicia sativa seedlings incubated aerobically with [1-14C]oleic acid (Z9-octadecenoic acid) or [1-14C]9,10-epoxystearic acid or [1-14C]9,10-dihydroxystearic acid catalyzed the NADPH-dependent formation of hydroxylated metabolites. The chemical structure of compounds formed from oleic, 9,10-epoxystearic or 9,10-dihydroxystearic acids was established by gas chromatography/mass spectra analysis to be 18-hydroxyoleic acid, 18-hydroxy-9,10-epoxystearic acid and 9,10,18-trihydroxystearic acid, respectively. The reactions required O2 and NADPH and were inhibited by carbon monoxide. As expected for monooxygenase reactions involving cytochrome P450, inhibition could be partially reversed by light and all three reactions were inhibited by antibodies raised against NADPH-cytochrome P450 reductase from Jerusalem artichoke. The omega-hydroxylation of the three substrates was enhanced in microsomes from clofibrate induced seedlings. 相似文献
103.
104.
Both the Entamoeba histolytica lectin, a virulence factor for the causative
agent of amebiasis, and the mammalian hepatic lectin bind to
N-acetylgalactosamine (GalNAc) and galactose (Gal) nonreducing termini on
oligosaccharides, with preference for GalNAc. Polyvalent GalNAc-
derivatized neoglycoproteins have >1000-fold enhanced binding affinity
for both lectins (Adler,P., Wood,S.J., Lee,Y.C., Lee,R.T., Petri,W.A.,Jr.
and Schnaar,R.L.,1995, J. Biol. Chem ., 270, 5164-5171). Substructural
specificity studies revealed that the 3-OH and 4-OH groups of GalNAc were
required for binding to both lectins, whereas only the E.histolytica lectin
required the 6-OH group. Whereas GalNAc binds with 4-fold lower affinity to
the E.histolytica lectin than to the mammalian hepatic lectin,
galactosamine and N-benzoyl galactosamine bind with higher affinity to the
E. histolytica lectin. Therefore, a synthetic scheme for converting
polyamine carriers to poly-N-acyl galactosamine derivatives (linked through
the galactosamine primary amino group) was developed to test whether such
ligands would bind the E.histolytica lectin with high specificity and high
affinity. Contrary to expectations, polyvalent derivatives including
GalN6lys5, GalN4desmosine, GalN4StarburstTMdendrimer, and
GalN8StarburstTMdendrimer demonstrated highly enhanced binding to the
mammalian hepatic lectin but little or no enhancement of binding to the
E.histolytica lectin. We propose that the mammalian hepatic lectin binds
with greatest affinity to GalNAc "miniclusters," which mimic branched
termini of N-linked oligosaccharides, whereas the E.histolytica lectin
binds most effectively to "maxiclusters," which may mimic more widely
spaced GalNAc residues on intestinal mucins.
相似文献
105.
106.
Ecdysterone biosynthesis: a microsomal cytochrome-P-450-linked ecdysone 20-monooxygenase from tissues of the African migratory locust. 总被引:1,自引:0,他引:1
Ecdysone 20-monooxygenase, an enzyme which converts ecdysone to ecdysterone (the major moulting hormone of insects) has been characterized in cell-free preparations of tissues from African migratory locust. The product of the reaction has been identified as ecdysterone on the basis of several microchemical derivatization and chromatographic methods. Ecdysone 20-monooxygenase activity is located primarily in the microsomal fraction which also carries NADPH cytochrome c reductase and cytochrome P-450, as shown by sucrose density gradient centrifugation. Optimal conditions for the ecdysone 20-monooxygenase assay have been determined. The enzyme has a Km for ecdysone of 2.7 x 10(-7) M and is competitvely inhibited by ecdysterone (Ki = 7.5 x 10(-7) M). Ecdysone 20-monooxygenase is a typical cytochrome P-450 linked monooxygenase: the reaction requires O2 and is inhibited by CO, an effect partially reversed by white light. The enzyme is effectively inhibited by several specific monooxygenase inhibitors and by sulfhydryl reagents, but not by cyanide ions. Ecdysone elicits a type I difference spectrum when added to oxidized microsomes. NADPH acts as preferential electron donor. The transfer of reducing equivalents proceeds through NADPH cytochrome c (P-450) reductase: ecdysone 20-monooxygenase is inhibited by cytochrome c. Both NADPH cytochrome c reductase and ecdysone 20-monooxygenase are inhibited by NADP+ and show a similar Km for NADPH. The Malpighian tubules have the highest specific activity of ecdysone 20-monooxygenase, while fat body contain most of the cytochrome P-450 and NADPH cytochrome c reductase. 相似文献
107.
High risk populations and HIV-1 infection in China 总被引:1,自引:0,他引:1
Tuo Fu ZHU- * Chun Hui WANG Peng LIN Na HE Departments of Laboratory Medicine Departments of Microbiology University of Washington School of Medicine Seattle WA USA Programs in Infectious Diseases Fred Hutchinson Cancer Research Center Seattle WA - USA Guangdong Center for Disease Control Prevention Guangzhou China School of Public Health Fudan University Shanghai China 《Cell research》2005,(Z1)
INTRODUCTION HIV has spread to all of China’s 31 provinces, autono- mous regions and municipalities, creating one of the fast- est-growing HIV/AIDS epidemics in the world [1,2]. The HIV/AIDS epidemic in China has gone through three phases: the Entry Phase (1985 -1988), the Spreading Phase (1989-1994) and the Expansion Phase (1995- present). The striking increase of HIV-1 infections over the past few years may herald entry into a new fourth phase that will include much larger nu… 相似文献
108.
R Le Bouquin M Skrabs R Kahn I Benveniste J P Salaün L Schreiber F Durst F Pinot 《European journal of biochemistry》2001,268(10):3083-3090
A full length cDNA encoding a new cytochrome P450-dependent fatty acid hydroxylase (CYP94A5) was isolated from a tobacco cDNA library. CYP94A5 was expressed in S. cerevisiae strain WAT11 containing a P450 reductase from Arabidopsis thaliana necessary for catalytic activity of cytochrome P450 enzymes. When incubated for 10 min in presence of NADPH with microsomes of recombinant yeast, 9,10-epoxystearic acid was converted into one major metabolite identified by GC/MS as 18-hydroxy-9,10-epoxystearic acid. The kinetic parameters of the reaction were Km,app = 0.9 +/- 0.2 microM and Vmax,app = 27 +/- 1 nmol x min(-1) x nmol(-1) P450. Increasing the incubation time to 1 h led to the formation of a compound identified by GC/MS as 9,10-epoxy-octadecan-1,18-dioic acid. The diacid was also produced in microsomal incubations of 18-hydroxy-9,10-epoxystearic acid. Metabolites were not produced in incubations with microsomes of yeast transformed with a control plasmid lacking CYP94A5 and their production was inhibited by antibodies raised against the P450 reductase, demonstrating the involvement of CYP94A5 in the reactions. The present study describes a cytochrome P450 able to catalyze the complete set of reactions oxidizing a terminal methyl group to the corresponding carboxyl. This new fatty acid hydroxylase is enantioselective: after incubation of a synthetic racemic mixture of 9,10-epoxystearic acid, the chirality of the residual epoxide was 40/60 in favor of 9R,10S enantiomer. CYP94A5 also catalyzed the omega-hydroxylation of saturated and unsaturated fatty acids with aliphatic chain ranging from C12 to C18. 相似文献
109.
Thrombosis plays a major role in acute vessel closure both after coronary balloon angioplasty and after stenting. This review will address the role of antiplatelet and anticoagulant therapy in preventing early thrombotic complications after percutaneous coronary intervention. The focus will be on agents that are routinely available and commonly used. 相似文献
110.
Chichirau A Flueraru M Chepelev LL Wright JS Willmore WG Durst T Hussain HH Charron M 《Free radical biology & medicine》2005,38(3):344-355
ortho-Hydroxyphenols (catechols) form a common structural unit in naturally occurring antioxidants such as polyphenols. They also show pro-oxidant characteristics which depend on their particular structure. Here we examined the acetylated versions of three catechols and a naphthalenediol for cytotoxicity to adrenal PC12-AC cells. We found that the three catechols H1 (a p-methoxycatechol), H2 (a catechol analog of alpha-tocopherol), and H4 (a dioxymethylene-substituted catechol) strongly upregulate glutathione (GSH) in 24 h, whereas 1,4-dipropyl-2,3-naphthalenediol (DPND) does not. Upregulation of GSH is primarily caused by oxidative stress in the form of hydrogen peroxide generation, and both GSH upregulation and the rate of H(2)O(2) generation correlate well with the cytotoxicity. The major source of H(2)O(2) is autoxidation in the extracellular space, which results from transport of the (deacetylated) hydroquinone form outside the cell, rather than internal redox cycling. DPND is much less cytotoxic than any of the catechols. We show that this is because it cannot form a naphthoquinone due to the energy penalty associated with the loss of aromaticity in the benzene ring adjacent to the diol functional group. The relevance of these results to the design of antioxidants is discussed. 相似文献