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971.
In this study, the effect of temperature on the stereoselectivity of phospholipase D (PLD) toward the two primary hydroxyl
groups of glycerol in the transphosphatidylation reaction of phosphatidylcholine to phosphatidylglycerol (PtdGro) was investigated.
For this purpose, PLD from bacteria (Streptomyces septatus TH-2, S. halstedii subsp. scabies K6, and Actinomadura sp.) and cabbage were tested. At the reaction temperatures employed (0–60°C), the proportions of the two PtdGro diastereomers,
namely, 1,2-dioleoyl-sn-glycero-3-phospho-3′-sn-glycerol (R,R configuration) and 1,2-dioleoyl-sn-glycero-3-phosphol-1′-sn-glycerol (R,S configuration), which were produced with PLD from Streptomyces TH-2 and Actinomadura sp., changed gradually from 50% R,R and 50% R,S at 50–60°C to 70% R,R and 30% R,S at O°C. These alterations suggested that the stereoselectivity of the bacterial PLD toward the two primary hydroxyl groups
of prochiral glycerol was significantly influenced by reaction temperature. PLD from Streptomyces K6 showed relatively little effect of temperature on stereoselectivity, giving 65–69% R,R in the temperature range of 60–10°C examined. The plots of In ([R,R]/[R,S]) vs. 1/T gave good linear fits for these three bacterial PLD. No temperature effect was observed for cabbage PLD, which gave an almost
equimolar mixture of the R,R and R,S diastereomers in the range from 0 to 40°C. The temperature-dependent change in enantiomeric selectivity of the bacterial
PLD promises potentially profitable commercial exploitation. 相似文献
972.
The concentrations of CLA isomers were determined by Ag+-HPLC in the milk fat of cows fed a control diet consisting of hay ad libitum and 15 kg of fodder beets or this diet supplemented with oilseeds containing either high levels of oleic acid (rapeseed),
linoleic acid (sunflower seed), or α-linolenic acid (linseed). Highly significant (P≤0.001) correlations were found between the daily intakes of oleic acid and the concentration of the CLA isomer trans-7,cis-9 in milk fat; of linoleic acid and the CLA isomers trans-10,trans-12, trans-9,trans-11, trans-8,trans-10, trans-7,trans-9, trans-10,cis-12, cis-9,trans-11, trans-8,cis-10, and trans-7,cis-9; and of α-linolenic acid and the CLA isomers trans-12,trans-14, trans-11,trans-13, cis,trans/trans,cis-12,14, trans-11,cis-13, and cis-11,trans-13. CLA concentrations were also determined in the milk fat of cows grazing in the lowlands (600–650 m), the mountains (900–1210
m), and the highlands (1275–2120 m). The concentrations of many isomers were highest in milk fat from the highlands, but only
three CLA isomers (cis-9,trans-11, trans-11,cis-13, and trans-8,cis-10) showed a nearly linear increase with elevation. Therefore, these three CLA isomers, and particularly the CLA isomer trans-11,cis-13, the second-most important CLA in milk fat from cows grazing at the three altitudes, could be useful indicators of milk
products of Alpine origin. 相似文献
973.
Nesaretnam K Ambra R Selvaduray KR Radhakrishnan A Reimann K Razak G Virgili F 《Lipids》2004,39(5):459-467
It has recently been shown that tocotrienols are the components of vitamin E responsible for inhibiting the growth of human
breast cancer cells in vitro, through an estrogen-independent mechanism. Although tocotrienols act on cell proliferation in a dose-dependent manner and
can induce programmed cell death, no specific gene regulation has yet been identified. To investigate the molecular basis
of the effect of tocotrienols, we injected MCF-7 breast cancer cells into athymic nude mice. Mice were fed orally with 1 mg/d
of tocotrienol-rich fraction (TRF) for 20 wk. At end of the 20 wk, there was a significant delay in the onset, incidence,
and size of the tumors in nude mice supplemented with TRF compared with the controls. At autopsy, the tumor tissue was excised
and analyzed for gene expression by means of a cDNA array technique. Thirty out of 1176 genes were significantly affected.
Ten genes were down-regulated and 20 genes up-regulated with respect to untreated animals, and some genes in particular were
involved in regulating the immune system and its function. The expression of the interferon-inducible transmembrane protein-1
gene was significantly up-regulated in tumors excised from TRF-treated animals compared with control mice. Within the group
of genes related to the immune system, we also found that the CD59 glycoprotein precursor gene was up-regulated. Among the
functional class of intracellular transducers/effectors/modulators, the c-myc gene was significantly down-regulated in tumors
by TRF treatment. Our observations indicate that TRF supplementation significantly and specifically affects MCF-7 cell response
after tumor formation in vivo and therefore the host immune function. The observed effect on gene expression is possibly exerted independently from the
antioxidant activity typical of this family of molecules. 相似文献
974.
We identified and quantified the hydroperoxides, hydroxides, epoxides, isoprostanes, and core aldehydes of the major phospholipids
as the main components of the oxophospholipids (a total of 5–25 pmol/μmol phosphatidylcholine) in a comparative study of human
atheroma from selected stages of lesion development. The developmental stages examined included fatty streak, fibrous plaque,
necrotic core, and calcified tissue. The lipid analyses were performed by normal-phase HPLC with on-line electrospray MS using
conventional total lipid extracts. There was great variability in the proportions of the various oxidation products and a
lack of a general trend. Specifically, the early oxidation products (hydroperoxides and epoxides) of the glycerophosphocholines
were found at the advanced stages of the plaques in nearly the same relative abundance as the more advanced oxidation products
(core aldehydes and acids). The anticipated linear accumulation of the more stable oxidation products with progressive development
of the atherosclerotic plaque was not apparent. It is therefore suggested that lipid infiltration and/or local peroxidation
is a continuous process characterized by the formation and destruction of both early and advanced products of lipid oxidation
at all times. The process of lipid deposition appears to have been subject to both enzymatic and chemical modification of
the normal tissue lipids. Clearly, the appearance of new and disproportionate old lipid species excludes randomness in any
accumulation of oxidized LDL lipids in atheroma. 相似文献
975.
We describe a chip-based immunoassay for multiplex antigen detection, based on the self-assembly of semi-synthetic DNA-protein conjugates to generate an easily configurable protein microarray. The general principle of this microarray-fluorescence immunoassay (microFIA) is similar to that of a two-sided (sandwich) immunoassay. However, covalent single-stranded DNA-streptavidin conjugates are employed for the efficient immobilization of biotinylated capture antibodies through hybridization to complementary surface-bound DNA oligomers. In a model system, we use the DNA-directed immobilization (DDI) of antibodies to generate an antibody microarray for the parallel detection of the tumor marker human carcinoembryonic antigen (CEA), recombinant mistletoe lectin rViscumin (rVis), ceruloplasmin (CEP), and complement-1-inactivator (C1A) in human blood serum samples. Detection limits down to 400 pg mL(-1) are reached. In addition, we describe a method for the internal standardization of protein microarray analyses, based on the simultaneous measurement of constant amounts of the blood proteins CEP and C1 A, intrinsically present in human serum, to compensate for interexperimental variations usually occurring in microarray analyses. The standardization leads to a significantly higher data reliability and reproducibility in intra- and interassay measurements. We further demonstrate that the DDI-microFIA can also be carried out in a single step by tagging of the analyte simultaneously with both capture and detection antibody and subsequent immobilization of the immunocomplex formed, on the DNA microarray capture matrix. This protocol significantly reduces handling time and costs of analysis. 相似文献
976.
Jarau S Hrncir M Ayasse M Schulz C Francke W Zucchi R Barth FG 《Journal of chemical ecology》2004,30(4):793-804
By depositing scent marks on flowers, bees reduce both the search time and the time spent with the handling of nonrewarding flowers. They thereby improve the efficiency of foraging. Whereas in honey bees the source of these scent marks is unknown, it is assumed to be the tarsal glands in bumble bees. According to histological studies, however, the tarsal glands lack any openings to the outside. Foragers of the stingless bee Melipona seminigra have previously been shown to deposit an attractant pheromone at sugar solution feeders, which is secreted at the tips of their tarsi. Here we show that the claw retractor tendons have specialized glandular epithelia within the femur and tibia of all legs that produce this pheromone. The secretion accumulates within the hollow tendon, which also serves as the duct to the outside, and is released from an opening at the base of the unguitractor plate. In choice experiments, M. seminigra was attracted by feeders baited with pentane extracts of the claw retractor tendons in the same way as it was attracted by feeders previously scent marked by foragers. Our results resolve the seeming contradiction between the importance of foot print secretions and the lack of openings of the tarsal glands. 相似文献
977.
Numbers of Lucilia cuprina (Australian sheep blowfly), Chrysomya spp., and Calliphora spp. blowflies caught on sticky traps baited with various synthetic attractants or a standard liver/sodium sulfide attractant in western Queensland were recorded. Numbers of each genus collected were influenced by the composition of the chemical attractants. Attractant mixtures based on 2-mercaptoethanol, indole, butanoic/pentanoic acid, and a sodium sulfide solution gave 5- to 20-fold higher L. cuprina catches than the liver standard. These blends attracted similar numbers of Chrysomya spp. (0.85-2.7x) and fewer Calliphora spp. (0.02-0.2x) compared to the liver standard. These synthetic attractants were more effective and selective for L. cuprina than the standard liver/sodium sulfide attractant, and they can be packaged in controlled-release dispensers to generate constant, prolonged release of the attractant. 相似文献
978.
Allemann C Gordillo R Clemente FR Cheong PH Houk KN 《Accounts of chemical research》2004,37(8):558-569
Computational studies have led to models to understand some classic and contemporary asymmetric reactions involving organocatalysts. The Hajos-Parrish-Eder-Sauer-Wiechert reaction and intermolecular aldol reactions as well as Mannich reactions and oxyaminations catalyzed by proline and other amino acids, and Diels-Alder reactions catalyzed by MacMillan's chiral amine organocatalysts have been studied with density functional theory. Quantitative predictions for several new catalysts and reactions are provided. 相似文献
979.
González-Coloma A Reina M Medinaveitia A Guadaño A Santana O Martínez-Díaz R Ruiz-Mesía L Alva A Grandez M Díaz R Gavín JA De la Fuente G 《Journal of chemical ecology》2004,30(7):1393-1408
We have tested the insect antifeedant and toxic activity of 43 norditerpenoid alkaloids on Spodoptera littoralis and Leptinotarsa decemlineata including eserine (physostigmine), anabasine, and atropine. Antifeedant effects of the test compounds were structure- and species-dependent. The most active antifeedants to L. decemlineata were 1,14-diacetylcardiopetaline (9) and 18-hydroxy- 14-O-methylgadesine (33), followed by 8-O-methylconsolarine (12), 14-O-acetyldelectinine (27), karakoline (7), cardiopetaline (8), 18-O-demethylpubescenine (13), 14-O-acetyldeltatsine (18), takaosamine (21), ajadine (24), and 8-O-methylcolumbianine (6) (EC50 < 1 microg/cm2). This insect showed a moderate response to atropine. S. littoralis had the strongest antifeedant response to 24, 18, 14-O-acetyldelcosine (19), and delphatine (29) (EC50 < 3 microg/cm2). None of the model substances affected the feeding behavior of this insect. The most toxic compound to L. decemlineata was aconitine (1), followed by cardiopetalidine (10) (% mortality > 60), 14-deacetylpubescenine (14), 18-O-benzoyl-18-O-demethyl-14-O-deacetylpubescenine (17), 14-O-acetyldelcosine (19), 14-deacetylajadine (25) and methyllycaconitine (30) (% mortality > 45). Orally injected S. littoralis larvae were negatively affected by 1, cardiopetaline (8), 10, 1,14-O-acetylcardiopetalidina (11), 12, 14, 1,18-O-diacetyl-19-oxo-gigactonine (41), olivimine (43), and eserine in varying degrees. Their antifeedant or insecticidal potencies did not parallel their reported nAChR binding activity, but did correlate with the agonist/antagonist insecticidal/antifeedant model proposed for nicotininc insecticides. A few compounds [14, tuguaconitine (38), 14-demethyldelboxine (40), 19, dehydrodelsoline (36), 18-O-demethylpubescenine (13), 41, 9, and delcosine (23)] had selective cytotoxic effects to ward insect-derived Sf9 cells. None were cytotoxic to mammalian CHO cells and none increased Trypanosoma cruzi mortality. The selective cytotoxic effects of some structures indicate that they can act on biological targets other than neuroreceptors. 相似文献
980.
Lee PC Mijts BN Petri R Watts KT Schmidt-Dannert C 《Protein engineering, design & selection : PEDS》2004,17(11):771-777
Directed evolution of the C25 farnesylgeranyl diphosphate synthase of Aeropyrum pernix (Fgs) was carried out by error-prone PCR with an in vivo color complementation screen utilizing carotenoid biosynthetic pathway enzymes. Screening yielded 12 evolved clones with C20 geranylgeranyl diphosphate synthase activity which were isolated and characterized in order to understand better the chain elongation mechanism of this enzyme. Analysis of these mutants revealed three different mechanisms of product chain length specificity. Two mutants (A64T and A64V) have a single mutation at the 8th amino acid upstream of a conserved first aspartate-rich motif (FARM), which is involved in the mechanism for chain elongation reaction of all prenyl diphosphate synthases. One mutant (A135T) carries a single mutation at the 7th amino acid upstream of another conserved region (141GQ142), which was recently found to be another important region controlling chain elongation of a type III C20 geranylgeranyl diphosphate synthase and Escherichia coli C15 farnesyl diphosphate synthase. Finally, one mutant carrying four mutations (V84I, H88R, I177 M and M191V) is of interest. Molecular modeling, site-directed mutagenesis and in vitro assays of this mutant suggest that product chain-length distribution can be also controlled by a structural change provoked by a cooperative interaction of amino acids. 相似文献