共查询到20条相似文献,搜索用时 31 毫秒
1.
Dianyu Yu Lianzhou Jiang Zhenlan Li John Shi Jun Xue Yukio Kakuda 《Journal of the American Oil Chemists' Society》2012,89(4):649-656
Phospholipase A1 (PLA1), or Lecitase® Ultra, was immobilized on three different supports, calcium alginate (CA), calcium alginate-chitosan (CAC), and calcium alginate-gelatin (CAG), and crosslinked with glutaraldehyde. The results indicated that PLA1–CA retained 56.2% of the enzyme’s initial activity, whereas PLA1–CAC and PLA1–CAG retained 65.5 and 60.2%, respectively. Compared with free PLA1, the optimal pH of immobilized PLA1 shifted to the basic side by 0.5–1.0 pH units and the pH/activity profile range was considerably broadened. Similarly, the temperature-optima of PLA1–CAC and PLA1–CAG increased from 50 to 60 °C, and their thermal stability increased with relative activities of more than 90% that covered a wider temperature range spanning 50–65 °C. In a batch oil degumming process, the final residual phosphorus content was reduced to less than 10 mg/kg with free PLA1, PLA1–CAC and PLA1–CA in less than 5, 6 and 8 h respectively while PLA1–CAG was only able to reduce it to 15 mg/kg in 10 h. When the PLA1–CAC was applied in a plant degumming trial, the final residual phosphorus content was reduced to 9.7 mg/kg with 99.1% recovery of soybean oil. The recoveries of immobilized PLA1–CAC and activity of PLA1 were 80.2 and 78.2% respectively. Therefore, it was concluded that PLA1–CAC was the best immobilized enzyme complex for the continuous hydrolysis of phospholipids in crude vegetable oils. 相似文献
2.
Long Shuang Huang Mee Ree Kim Dai‐Eun Sok 《European Journal of Lipid Science and Technology》2009,111(6):584-592
Some lipid peroxides are known to be converted to their corresponding alcohols in cells containing glutathione peroxidase (GPx). In this respect, we examined the enzymatic conversion of lysophosphatidylcholine (lysoPC) hydroperoxides to hydroxyl derivatives using RBL‐2H3 cells and erythrocyte GPx‐1. First, the incubation of RBL‐2H3 cells with arachidonoyl lysoPC led to the formation of a major product, with maximal UV absorbance at 234 nm and m/z [M+H]+ at 560.2, corresponding to monohydroxyeicosatetraenoyl lysoPC. Similarly, linoleoyl lysoPC was also converted to its hydroxyl derivative in RBL‐2H3 cells. Separately, lysoPC hydroperoxide, generated from soybean lipoxygenase 1‐catalyzed oxygenation of linoleoyl lysoPC, arachidonoyl lysoPC or docosahexaenoyl lysoPC, was converted by GPx‐1 to the corresponding hydroxyl derivatives. When the kinetic values were determined, the Km values (3.1–32.3 µM) of the polyunsaturated lysoPC hydroperoxides increased with decreasing number of double bonds, in contrast to a similar value of Vm among them. Moreover, the catalytic efficiency of docosahexaenoyl lysoPC hydroperoxide was much greater than that of H2O2 as substrate of GPx‐1. In related experiments, where phosphatidylcholine hydroperoxides were incubated with phospholipase A2 and GPx‐1, the complete conversion of phosphatidylcholine hydroperoxides to hydroxyl derivatives was confirmed by LC/MS. Taken together, it is proposed that GPx‐1‐type enzymes may participate in the conversion of polyunsaturated lysoPC hydroperoxides to hydroxyl derivatives in cell systems. 相似文献
3.
Phospholipase A2 (PLA2) activity was investigated in various tissues of tobacco (Nicotiana tabacum). PLA2 activity in the flower was 15 times higher than that in the leaf, stem, and root. PLA2 activity in the flower appears to have originated from both Ca2+-dependent and-independent PLA2. A cDNA clone for protein with homology to animal secretory PLA2 (sPLA2), denoted as Nt PLA2, was isolated from the tobacco flower. The cDNA of Nt PLA2 encoded a mature protein of 127 amino acid residues with a putative signal peptide of 30 residues. The amino acid sequence
for mature Nt PLA2 contains 12 cysteines, a Ca2+ binding loop, and a catalytic domain that are commonly conserved in animal sPLA2. The Nt PLA2 mRNA was mainly expressed in the root and stem of tobacco. The recombinant Nt PLA2 was expressed as a fusion protein with thioredoxin in Escherichia coli. From the bacterial cell lysate, the fusion protein was recovered in soluble form and cleaved by Factor Xa proteinase. Then
the recombinant mature Nt PLA2 was purified by ion exchange chromatography. It was discovered that the purified Nt PLA2 essentially requires Ca2+, for the enzyme activity when the activity was determined using mixed-micellar phospholipid substrates with sodium cholate.
The optimal activity of Nt PLA2 was at pH 8–10 when PC was used as a substrate. 相似文献
4.
A. Mukherjee N. Krishnamurthy 《International Journal of Self-Propagating High-Temperature Synthesis》2010,19(4):237-243
The direct preparation of V-Ti solid solution alloy by coreduction of V2O5 and TiO2 with Al in an attritor mill was investigated. The reduction of V2O5 with Al is highly exothermic, whereas reduction of TiO2 with Al is not sufficiently exothermic for a self-sustaining reaction. A range of compositions of a mixture of V2O5 and TiO2 can be so chosen as to make the overall reduction of V2O5 and TiO2 with Al sufficiently exothermic for a self-sustaining reaction. Initial studies were done to identify the reaction products
obtained by reducing V2O5 with Al. The reaction yielded the intermetallic phase (Al3V), V, and Al2O3. SEM images indicated melting and solidification of the phases, leading to agglomeration. Further experiments involved mixing
appropriate amounts of TiO2 with V2O5 and reducing the mixture with Al. XRD data for products showed the presence of V, V5Al8, and Al2O3. X-Ray Florescence (XRF) analysis and energy dispersive analyzer (EDAX) of SEM sample images indicated the formation of V-Ti
solid solution. Microstructure of the milled charges taken out prior to reaction initiation indicated morphology change in
Al powder and agglomeration/segregation of reactants. As a result, the reaction of V2O5 with the excess Al at certain regions also promoted the formation of vanadium aluminide. 相似文献
5.
Hydrolysis of Phosphatidylcholine-Isoprostanes (PtdCho-IP) by Peripheral Human Group IIA,V and X Secretory Phospholipases A<Subscript>2</Subscript> (sPLA<Subscript>2</Subscript>)
下载免费PDF全文
![点击此处可从《Lipids》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Biologically active F- and E/D-type-prostane ring isomers (F2-IP and E2/D2-IP, respectively) are produced in situ by non-enzymatic peroxidation of arachidonic acid esterified to GroPCho (PtdCho-IP) and are universally distributed in tissue lipoproteins and cell membranes. Previous work has shown that platelet-activating factor acetylhydrolases (PAF-AH) are the main endogenous PLA2 involved in degradation of PtdCho-IP. The present study shows that the PtdCho-IP are also subject to hydrolysis by group IIA, V and X secretory PLA2, which also have a wide peripheral tissue distribution. For this demonstration, we compared the LC/MS profiles of PtdCho-IP of auto-oxidized plasma lipoproteins after incubation for 1–4 h (37 °C) in the absence or presence of recombinant human sPLA2 (1–2.5 µg/ml). In the absence of exogenously added sPLA2 the total PtdCho-IP level after 4 h incubation reached 15.9, 21.6 and 8.7 nmol/mg protein of LDL, HDL and HDL3, respectively. In the presence of group V or group X sPLA2 (2.5 µg/ml), the PtdCho-IP was completely hydrolyzed in 1 h, while in the presence of group IIA sPLA2 (2.5 µg/ml) the hydrolysis was less than 25% in 4 h, although it was complete after 8–24 h incubation. This report provides the first demonstration that PtdCho-IP are readily hydrolyzed by group IIA, V and X sPLA2. A co-location of sPLA2 and the substrates in various tissues has been recorded. Thus, the initiation of interaction and production of isoprostanes in situ are highly probable. 相似文献
6.
T. I. Panova V. P. Popov V. B. Glushkova A. V. Domanskii 《Glass Physics and Chemistry》2007,33(6):652-657
A procedure for preparing solid solutions based on zirconium and hafnium hydroperoxides is developed. This procedure is based on the coprecipitation of components in the presence of hydrogen peroxide. Amorphous nanopowders (S sp = 80–90 m2/g, d mean = 2–3 nm) without any indication of the agglomeration of particles are synthesized. After the decomposition of complex hydroperoxides at a temperature of 500°C, the compacted powders undergo an active sintering at a temperature of 1450°C. The particle size after heat treatment does not exceed 50 nm. As follows from the electrical and physical characteristics obtained for these materials, they can be recommended for the use as solid electrolytes and sensors of oxygen partial pressure. 相似文献
7.
Membrane lipid metabolism and phospholipase activity in insect Spodoptera frugiperda 9 ovarian cells
Although there is increasing use of insect ovarian Sf9 cells for the production of recombinant proteins, namely, via the baculovirus
vector expression system, little is known about the lipids in the cell membrane and whether endogenous phospholipases are
present for regulation of the cell membrane lipids. In this study, analysis of membrane lipids of Sf9 cells indicated the
presence of phosphatidylethanolamine (PE) (diacyltype) and phosphatidylcholine as major phospholipids, followed by phosphatidylserine
and phosphatidylinositol (PI), and only trace amounts of ethanolamine plasmalogen. These phospholipids contain high proportions
of monoenoic fatty acids, e.g., 16∶1 and 18∶1, which comprise more than 70% of the total fatty acids although small amounts
of polyunsaturated fatty acids such as 18∶2 and 20∶4 are also present. When Sf9 cells were incubated in a culture medium containing
[14C]oleic acid and [14C]arachidonic acid, a large portion of the labels were incorporated into membrane phospholipids. Using [14C]arachidonoyl-phospholipids as substrates for incubation with cell homogenate and subcellular fractions, results indicate
the presence of a Ca2+-independent phospholipase A (PLA2) in the Sf9 cell cytosol fraction. This PLA2 shows a high preference for hydrolysis of PE and is active at a pH range of 7–9. Unlike the brain cells which contain active
phospholipase C (PLC) specific for phosphatidylinositol, only limited amount of diacylglycerol (DAG) was released from [14C]arachidonoyl-PE in the Sf9 cells. Taken together, this study demonstrates active metabolism of membrane phospholipids in
Sf9 cells, most likely mediated by acyltransferases and PLA2. Furthermore, despite the absence of PLC for PI, limited amount of DAG could be generated through hydrolysis of PE. 相似文献
8.
Min Kang Jinsoon Choi Yong Tae Kim Eun Duck Park Chee Burm Shin Dong Jin Suh Jae Eui Yie 《Korean Journal of Chemical Engineering》2009,26(3):884-889
A series of V2O5-TiO2 aerogel catalysts were prepared by the sol-gel method with subsequent supercritical drying with CO2. The main variables in the sol-gel method were the amounts of V2O5 and when the vanadium precursor was introduced. V2O5-TiO2 xerogel and V2O5/TiO2 (P-25) were also prepared for comparison. The V2O5-TiO2 aerogel catalysts showed much higher surface areas and total pore volumes than V2O5-TiO2 xerogel and impregnated V2O5/TiO2 (P-25) catalysts. The catalysts were characterized by N2 physisorption, X-ray diffraction (XRD), FT-Raman spectroscopy, temperature-programmed reduction with H2 (H2-TPR), and temperature-programmed desorption of ammonia (NH3-TPD). The selective catalytic reduction of NOx with ammonia in the presence of excess O2 was studied over these catalysts. Among various V2O5-TiO2 catalysts, V2O5 supported on aerogel TiO2 showed a wide temperature window exhibiting high NOx conversions. This superior catalytic activity is closely related to
the large amounts of strong acidic sites as well as the surface vanadium species with characteristics such as easy reducibility
and monomeric and polymeric vanadia surface species.
This work was presented at the 7
th
Korea-China Workshop on Clean Energy Technology held at Taiyuan, Shanxi, China, June 26–28, 2008. 相似文献
9.
We characterized phospholipase A2 (PLA2) activity in isolated rabbit ventricular myocytes with respect to subcellular distribution, substrate specificity, and Ca2+ dependency. Membrane-associated PLA2 was found to be an order of magnitude greater than cytosolic PLA2. Ventricular myocyte PLA2 activity was enhanced following protease-activated receptor stimulation with thrombin and was found to be largely Ca2+-independent and selective for phospholipid substrates containing arachidonic acid at the sn-2 position. Immunoblot analysis using an antibody to cytosolic Ca2+-independent PLA2 from Chinese hamster ovary cells recognized a membrane-associated protein with a molecular mass of approximately 80 kDa;
however, differences in pH optima, response to inhibitors, and substrate selectivity of membrane-associated and cytosolic
PLA2 activity suggest the presence of multiple Ca2+-independent PLA2. Pretreatment with bromoenol lactone, a specific inhibitor of Ca2+-independent PLA2, significantly attenuated membrane-associated and cytosolic PLA2 in unstimulated and thrombin-stimulated myocytes. Pretreatment with methyl arachidonyl fluorophosphonate, mepacrine, or dibucaine
had no significant effect on PLA2 activity under all conditions tested. Ventricular myocyte PLA2 activity was significantly inhibited by ATP, GTP, and their nonhydrolyzable analogs and was regulated by protein kinase C
activity. These studies demonstrate the presence of one or more unique membrane-associated Ca2+-independent PLA2 in isolated ventricular myocytes that exhibit a preference for phospholipids with arachidonate at the sn-2 position and that are activated by thrombin stimulation. 相似文献
10.
Renée Grataroli Jeannie Léonardi Monique Charbonnier Raymond Lafont Huguette Lafont Gilles Nalbone 《Lipids》1988,23(7):666-670
Three groups of male rats were fed either a corn oilenriched diet (17%, w/w), a salmon oil-enriched diet (12.5%) supplemented
with corn oil (4.5%) or a low-fat diet (4.4%) for eight wk to investigate the possible relationships between dietary fatty
acids and lipid composition, and prostaglandin E2 level and phospholipase A2 activity in the rat gastric mucosa.
High-fat diets induced no important variation in total protein, phospholipid and cholesterol contents of gastric mucosa.
Compared with a low-fat diet, corn oil produced a higher n−6/n−3 ratio in mucosal lipids, whereas this ratio was markedly
lowered by a fish oil diet.
In comparison with the low-fat diet, the production of prostaglandin E2(PGE2) in gastric mucosa of rats fed salmon oil was significantly, decreased by a factor of 2.8. In the corn oil group, PGE2 production tended to decrease, but not significantly.
In comparison with the low-fat diet, both specific and total gastric mucosal phospholipase A2 activities were increased (+18 and 23%, respectively) in the salmon oil group; they were unchanged in the corn oil group.
It is suggested that the decrease of gastric PGE2 in rats fed fish oil is not provoked by a decrease in phospholipase A2 activity but may be the result of the substitution of arachidonic acid by n−3 PUFA or activation of PGE2 catabolism. 相似文献
11.
Sang Ok Choi In Young Ahn Sang Heup Moon 《Korean Journal of Chemical Engineering》2009,26(5):1252-1258
Two types of CeO2-modified Ni/Al2O3 catalysts were prepared by a consecutive impregnation method with different sequences in the impregnation of Ni and CeO2, and their performance in autothermal reforming (ATR) of isooctane was investigated. Catalysts prepared by adding CeO2 prior to the addition of Ni, Ni/CeO2-Al2O3, produced larger amounts of hydrogen than those obtained using catalysts prepared by adding the two components in an opposite
sequence, Ni-CeO2/Al2O3. The results of H2 chemisorption and temperature-programmed reduction revealed that added CeO2 increased the dispersion of the Ni species on Al2O3 and suppressed the formation of NiAl2O4 in the catalyst such that large amounts of Ni species were present as NiO, the active species for the ATR. The elemental
and thermogravimetric analyses of deactivated catalysts indicated that Ni/CeO2-Al2O3, which showed a longer lifetime than Ni-CeO2/Al2O3, contained lesser amounts and different types of coke on the surface. 相似文献
12.
Dominik Bakalarz Edyta Korbut Zhengnan Yuan Bingchen Yu Dagmara Wjcik Aleksandra Danielak Katarzyna Magierowska Slawomir Kwiecie Tomasz Brzozowski Monika Marcinkowska Binghe Wang Marcin Magierowski 《International journal of molecular sciences》2021,22(10)
Hydrogen sulfide (H2S) is an endogenously produced molecule with anti-inflammatory and cytoprotective properties. We aimed to investigate for the first time if a novel, esterase-sensitive H2S-prodrug, BW-HS-101 with the ability to release H2S in a controllable manner, prevents gastric mucosa against acetylsalicylic acid-induced gastropathy on microscopic and molecular levels. Wistar rats were pretreated intragastrically with vehicle, BW-HS-101 (0.5–50 μmol/kg) or its analogue without the ability to release H2S, BW-iHS-101 prior to ASA administration (125 mg/kg, intragastrically). BW-HS-101 was administered alone or in combination with nitroarginine (L-NNA, 20 mg/kg, intraperitoneally) or zinc protoporphyrin IX (10 mg/kg, intraperitoneally). Gastroprotective effects of BW-HS-101 were additionally evaluated against necrotic damage induced by intragastrical administration of 75% ethanol. Gastric mucosal damage was assessed microscopically, and gastric blood flow was determined by laser flowmetry. Gastric mucosal DNA oxidation and PGE2 concentration were assessed by ELISA. Serum and/or gastric protein concentrations of IL-1α, IL-1β, IL-2, IL-4, IL-6, IL-10, IL-13, VEGF, GM-CSF, IFN-γ, TNF-α, and EGF were determined by a microbeads/fluorescent-based multiplex assay. Changes in gastric mucosal iNOS, HMOX-1, SOCS3, IL1-R1, IL1-R2, TNF-R2, COX-1, and COX-2 mRNA were assessed by real-time PCR. BW-HS-101 or BW-iHS-101 applied at a dose of 50 μmol/kg protected gastric mucosa against ASA-induced gastric damage and prevented a decrease in the gastric blood flow level. H2S prodrug decreased DNA oxidation, systemic and gastric mucosal inflammation with accompanied upregulation of SOCS3, and EGF and HMOX-1 expression. Pharmacological inhibition of nitric oxide (NO) synthase but not carbon monoxide (CO)/heme oxygenase (HMOX) activity by L-NNA or ZnPP, respectively, reversed the gastroprotective effect of BW-HS-101. BW-HS-101 also protected against ethanol-induced gastric injury formation. We conclude that BW-HS-101, due to its ability to release H2S in a controllable manner, prevents gastric mucosa against drugs-induced gastropathy, inflammation and DNA oxidation, and upregulate gastric microcirculation. Gastroprotective effects of this H2S prodrug involves endogenous NO but not CO activity and could be mediated by cytoprotective and anti-inflammatory SOCS3 and EGF pathways. 相似文献
13.
The selective oxidation of hydrogen sulfide containing excess water and ammonia was studied over vanadium oxide-based catalysts.
The investigation was focused on the role of V2O5, and phase cooperation between V2O5 and Bi2O3 in this reaction. The conversion of H2S continued to decrease since V2O5 was gradually reduced by treatment with H2S. The activity of V2O5 was recovered by contact with oxygen. A strong synergistic phenomenon in catalytic activity was observed for the mechanically
mixed catalysts of V2O5 and Bi2O3. Temperature-programmed reduction (TPR) and oxidation (TPO) and two bed reaction tests were performed to explain this synergistic
effect by the reoxidation ability of Bi2O3.
This paper is dedicated to Professor Wha Young Lee on the occasion of his retirement from Seoul National University. 相似文献
14.
A cDNA encoding protein with homology to plant secretory phospholipase A2 (sPLA2), denoted as Nt1 PLA2, was isolated from tobacco (Nicotiana tabacum). The cDNA encodes a mature protein of 118 amino acid residues with a putative signal peptide of 29 residues. The mature
form of Nt1 PLA2 has 12 cysteines, Ca2+ binding loop and catalytic site domain that are commonly conserved in plant sPLA2s. The recombinant Nt1 PLA2 was expressed as a fusion protein with thioredoxin in E. coli BL21 cells and was purified by an ion exchange chromatography after digestion of the fusion proteins by Factor Xa protease
to obtain the mature form. Interestingly, Nt1 PLA2 could hydrolyze the ester bond at the sn-1 position of glycerophospholipids as well as at the sn-2 position, when the activities were determined using mixed-micellar phospholipids with sodium cholate. Both activities for
the sn-1 and -2 positions of glycerophospholipids required Ca2+ essentially, and maximal activities were found in an alkaline region when phosphatidylcholine, phosphatidylglycerol or phosphatidylethanolamine
was used as a substrate. The level of Nt1 PLA2 mRNA was detected at a higher level in tobacco flowers than stem, leaves and roots, and was induced by salicylic acid. 相似文献
15.
Xiaohong Li Jun Ai Wenying Li Dongxiong Li 《Frontiers of Chemical Science and Engineering》2010,4(4):476-480
A co-precipitation method was employed to prepare Ni/Al2O3-ZrO2, Co/Al2 O3-ZrO2 and Ni-Co/Al2O3-ZrO2 catalysts. Their properties were characterized by N2 adsorption (BET), thermogravimetric analysis (TGA), temperature-programmed reduction (TPR), temperature-programmed desorption (CO2-TPD), and temperature-programmed surface reaction (CH4-TPSR and CO2-TPSR). Ni-Co/Al2O3-ZrO2 bimetallic catalyst has good performance in the reduction of active components Ni, Co and CO2 adsorption. Compared with mono-metallic catalyst, bimetallic catalyst could provide more active sites and CO2 adsorption sites (C + CO2 = 2CO) for the methane-reforming reaction, and a more appropriate force formed between active components and composite support (SMSI) for the catalytic reaction. According to the CH4-CO2-TPSR, there were 80.9% and 81.5% higher CH4 and CO2 conversion over Ni-Co/Al2O3-ZrO2 catalyst, and its better resistance to carbon deposition, less than 0.5% of coke after 4 h reaction, was found by TGA. The high activity and excellent anti-coking of the Ni-Co/Al2O3-ZrO2 catalyst were closely related to the synergy between Ni and Co active metal, the strong metal-support interaction and the use of composite support. 相似文献
16.
Sun Hee Park Byung-Hee Chun Sung Hyun Kim 《Korean Journal of Chemical Engineering》2011,28(2):402-408
The effect of La2O3 content in Ni-La-Zr catalyst was investigated for the autothermal reforming (ATR) of CH4. The catalysts were prepared by the coprecipitation method and had a mesoporous structure. Temperature programmed reduction
(TPR) and X-ray photoelectron spectroscopy (XPS) indicated that a strong interaction developed between Ni species and the
support with the addition of La2O3. Thermogravimetric analysis (TGA) and H2-pulse chemisorption showed that the addition of La2O3 led to well dispersed NiO molecules on the support. Ni-La-Zr catalysts gave much higher CH4 conversion than Ni-Zr catalyst. The Ni-La-Zr containing 3.2 wt% La2O3 showed the highest activity. The optimum conditions for maximal CH4 conversion and H2 yield were H2O/CH4=1.00, O2/CH4=0.75. Under these conditions, CH4 conversion of 83% was achieved at 700 °C. In excess O2 (O2/CH4>0.88), the catalytic activity was decreased due to sintering of the catalyst. 相似文献
17.
O. Yu. Sinelshchikova S. K. Kuchaeva I. A. Drozdova V. L. Ugolkov E. A. Vlasov S. A. Petrov 《Glass Physics and Chemistry》2011,37(4):433-440
The results of experimental studies of synthesis of the hollandite phase K2Ga2Ti6O16 using initial mixtures of different dispersion compositions obtained by two methods, i.e., mechanical dispersion (MD) (followed
by solid-phase sintering) and sol-gel method (Pechini method, MP), are reported. The catalytic properties of the obtained
materials in the reactions of carbon monoxide (CO) and hydrogen (H2) oxidation have been determined. It has been demonstrated that an increase in the catalytic activity in the CO oxidation
reaction is observed on the samples obtained using the sol-gel method, in which the hollandite phase content is higher and
crystallization is more complete. The samples obtained using the MD method are characterized by a low porosity and activity
in comparison with those produced by the Pechini method. 相似文献
18.
Four enzymes with phospholipase A1 (PLA1) activity were purified from the fruiting bodies of the basidiomycete Armillaria ostoyae. The enzymes (PLA1-1, -2, -3 and -4) showed similar isoelectric points (4.3, 3.9, 4.0 and 4.0) and apparent molecular masses in the range of 35–47 kDa. Mass spectrometric analyses of proteolytic fragments revealed sequences homologous to α/β-hydrolase fold enzymes. The enzymes share one conserved region with fungal phospholipases B and the active site sequence with bacterial esterases and PLA1s. PLA1-1 cleaves phospholipids and lysophospholipids with an optimum activity at pH 5.3. In contrast, PLA1-2, -3 and -4 are characterized by broad pH optima in the slightly acidic to neutral range and are additionally capable of hydrolyzing mono- and diglycerides as well as fatty acid methyl esters. All enzymes favor glycerol-based lipids with a single medium-sized fatty acid moiety in the sn-1 position but show reduced activity towards the corresponding 1,2-diacyl derivatives with bulky long-chain or inflexible saturated fatty acid moieties in the sn-2 position. The enzymes prefer zwitterionic phospholipid substrates and are unable to hydrolyze triglycerides. From the selectivity of these broad-spectrum α/β-hydrolase fold enzymes towards the different classes of their substrates a regiospecific steric hindrance and a head group recognition are concluded. 相似文献
19.
Mechanism of Phospholipid Hydrolysis for Oyster <Emphasis Type="Italic">Crassostrea plicatula</Emphasis> Phospholipids During Storage Using Shotgun Lipidomics
下载免费PDF全文
![点击此处可从《Lipids》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A fast and efficient shotgun lipidomics strategy was applied to analyze phospholipids (PL) in the oyster Crassostrea plicatula, including 29 species of phosphatidylcholine (PtdCho), 23 species of phosphatidylethanolamine (PtdEtn), 11 species of phosphatidylserine (PtdSer), 6 species of phosphatidylinositol (PtdIns), and 17 species of lysophospholipids (Lyso-PL). During storage at 4 °C for 7 days, the PL content decreased by 68.08%, but a significant increase in the FFA content was observed (from 63.11 to 318.72 μg/g). PtdCho and PtdIns decreased relatively by 64.97 and 67.49%, and PtdSer decreased most markedly by 74.15%. However, the PtdEtn content increased slightly during the early stages of storage but subsequently began to decrease. Moreover, PL with eicosapentaenoic acid (EPA-PL) and docosahexaenoic acid (DHA-PL) decreased by 51.77 and 50.61%, whereas plasmalogens were relatively stable showing only a 25.46% decrease. In particular, through enzyme activity analysis of lipase, phospholipase A1 (PLA1), phospholipase A2 (PLA2), phospholipase C (PLC), and phospholipase D (PLD), it was observed that the activities of all these enzymes increased at the early stage at 4 °C, but their activities were at lower levels when the oysters were stored at ?20 °C. During the storage period at 4 °C, correlation analysis suggests that the degradation of PtdCho was mostly correlated to PLA2 (p < 0.05), whereas PtdEtn and PtdSer were more markedly correlated to lipase and PLD, respectively. The above result indicates that the hydrolysis mechanism of PL during seafood storage was correlated to the lipid hydrolytic enzyme activities under different storage temperatures. 相似文献
20.
TiO2-Al2O3 mixed oxides with different compositions ranging from 40wt-% to 95wt-% of TiO2 were prepared by sol-gel method and impregnated with different amounts of VO x . Supports and catalysts were characterized by X-ray diffraction (XRD), physisorption, temperature preprogrammed reduction (H2-TPR), and ammonia temperature programmed desorption (NH3-TPD). TiO2 content in the support had obvious effect on the crystal structure, texture characteristic, acid property, and catalytic activity in dehydrogenation of ethylbenzene (EB) with carbon dioxide. The highest catalytic activity was acquired when the TiO2 content was 50 wt-%. 相似文献