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1.
Enzymatic synthesis of structured lipids from single cell oil of high docosahexaenoic acid content 总被引:1,自引:0,他引:1
Yugo Iwasaki Jeong Jun Han Miho Narita Roxana Rosu Tsuneo Yamane 《Journal of the American Oil Chemists' Society》1999,76(5):563-569
The lipase-catalyzed acidolysis of a single-cell oil (SCO) containing docosahexaenoic acid (DHA) and docosapentaenoic acid
(DPA) with caprylic acid (CA) was investigated. The targeted products were structured lipids containing CA residues at the
sn-1 and -3 positions and a DHA or DPA residue at the sn-2 position of glycerol. Rhizomucor miehei lipase (RML) and Pseudomonas sp. KWI-56 lipase (PSL) were used as the biocatalysts. When PSL was used > 60 mol% of total SCO fatty acids (FA) were exchanged
with CA, with DHA and DPA as well as the other saturated FA being exchanged. The content of the triacylglycerols (TG) containing
two CA and one DHA or DPA (number of carbon atoms = 41, i.e., C41) residue was high (36%), and the isomer with the desired configuration (unsaturated FA residue at the sn-2 position) represented 77–78% of C41. In the case of RML, CA content reached only 23 mol% in the TG. A large amount of DHA and DPA residues remained unexchanged
with RML, so that the resulting oil was rich in TG species containing two or three DHA or DPA residues (46%). TG C41 amounted to 22%, almost all of which had the desired configuration. This result suggested that the difference in the degree
of acidolysis by the two enzymes was due to their different selectivity toward DHA and DPA, as well as the difference in their
positional specificities. 相似文献
2.
Kazuo Watanabe Chikako Ishikawa Hitomi Inoue Deng Cenhua Kazunaga Yazawa Kiyosi Kondo 《Journal of the American Oil Chemists' Society》1994,71(3):325-330
Incorporation of exogenous docosahexaenoic acid (DHA) into bacterial phospholipids was examined as a method for DHA-linked
phospholipid production. The cultivation of 23 bacterial strains in medium with DHA showed that an eicosapentaenoic acid-producing
bacteriumShewanella sp. strain SCRC-2738 (strain SCRC-2738),Bacillus subtilis W23,B. cereus, an Antarctic marine bacterium strain S-7 (strain S-7), photosynthesis bacterium (PSB)Rhodopseudomonas capsulatus utilized for the production of larval marine fish,Pseudomonas aeruginosa, Staphylococcus aureus, Serratia marcescens andEscherichia coli K12 all incorporated DHA into their polar lipids. The polar lipids of the strain SCRC-2738, strain S-7, PSB andE. coli K12 were identified to be phospholipids. DHA was localized at thesn-2 position in the phospholipids of the four strains. Incorporation of exogenous DHA into their phospholipids produced an
increase in saturated fatty acids and a decrease in monounsaturated fatty acids exceptE. coli K12. The strain SCRC-2738 incorporated the largest amount of DHA into their phospholipids among the tested bacterial strains
in this study: DHA was 16% of the total fatty acids in the phosphatidylethanolamine (PE) and 29% in the phosphatidylglycerol
(PG). In the PSB, incorporated DHA was 12% of the total fatty acids in the PE, 10% in the PG and phosophatidylcholine so that
the PSB was nutritionally fortified. 相似文献
3.
Ann‐Marie Lyberg Dietlind Adlercreutz Patrick Adlercreutz 《European Journal of Lipid Science and Technology》2005,107(5):279-290
Regioselective incorporation of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) into phosphatidylcholine (PC) was carried out using enzymatic and chemical synthesis. Incorporation at the sn‐1 position was successfully achieved by lipase‐catalysed esterification of 2‐palmitoyl‐lysophosphatidylcholine (LPC), although in most cases, the enzymes incorporated EPA and DHA at lower rates than other fatty acids. For the incorporation of DHA, Candida antarctica lipase B was the only useful enzyme, while incorporation of EPA was efficiently carried out using either this enzyme or Rhizopus arrhizus lipase. The highest yields in the lipase‐catalysed reactions were obtained at the lowest water activity (close to 0). However, by carrying out the reactions at a higher water activity of 0.22, more EPA and DHA were incorporated. Esterification of 2‐palmitoyl‐LPC with pure EPA at this water activity converted 66 mol‐% of LPC to PC using Rhizopus arrhizus lipase as catalyst. When the fatty acid was DHA and the catalyst Candida antarctica lipase B, 45 mol‐% of PC was obtained. For incorporation of EPA and DHA at the sn‐2 position, phospholipase A2 was used, but the reaction was very slow. Chemical coupling of 1‐palmitoyl‐LPC and EPA or DHA was more efficient, resulting in complete conversion of LPC. 相似文献
4.
Stereospecific analysis was carried out to establish positional distribution of FA in the TAG of DHA, EPA, and (EPA+DHA)-enriched
oils. In this study, TAG of enzymatically modified oils were purified using a silicic acid column. The TAG were then subjected
to positional distribution analysis using a modified procedure involving reductive cleavage with Grignard reagent. The results
showed that in DHA-enriched borage oil (BO), DHA was randomly distributed over the three positions of TAG, whereas γ-linolenic
acid (GLA) was mainly esterified at the sn-2 and-3 positions. In DHA-enriched evening primrose oil (EPO), however, DHA and GLA were concentrated in the sn-2 position. In EPA-enriched BO, EPA was randomly distributed over the three positions of TAG, similar to that observed for
DHA. In EPA-enriched EPO, however, this FA was mainly located at the primary positions (sn-1 and sn-3) of TAG. In both oils, GLA was preferentially esterified at the sn-2 position. In (EPA+DHA)-enriched BO, EPA and DHA were mainly esterified at the sn-1 and -3 positions of TAG, whereas GLA was mainly located at the sn-2 position. In (EPA+DHA)-enriched EPO, GLA was mainly located at the sn-2 and-3 positions; EPA was preferentially esterified at the sn-1 and-3 positions, and DHA was found mainly at the sn-3 position. 相似文献
5.
The deposition oftrans-12-octadecenoate-12(13)-3H (12t-18∶1-3H) was compared tocis-9-octadecenoate-10-14C (9c-18∶1-14C) in the major egg yolk neutral lipids and phospholipids.trans-12-Octadecenoate was preferentially incorporated into cholesteryl esters (CE), phosphatidylcholines (PC), and phosphatidylethanolamines
(PE) but was discriminated against in triglycerides (TG). Isotopic ratios indicate that 5.9 and 5.6 times more 12t-18∶1-3H than 9c-18∶1-14C was esterified at the 1-acyl position of PE and PC, respectively. The combined 1- and 3-acyl positions of TG and the 2-acyl
position of TG, PE and PC were each preferentially esterified with 9c-18∶1-14C. 相似文献
6.
The time course of hydrolysis of a mixed phospholipid substrate containing bovine liver 1,2-diacyl-sn-glycero-3-phosphocholine (PC) and 1,2-diacyl-sn-glycero-3-phosphoethanolamine (PE) catalyzed byCrotalus adamanteus phospholipase A2 was measured before and after peroxidation of the lipid substrate. The rate of hydrolysis was increased after peroxidation
by an iron/adenosine diphosphate (ADP) system; the presence of iron/ADP in the assay had a minimal inhibitory effect. The
rate of lipid hydrolysis was also increased after the substrate was peroxidized by heat and O2. Similarly, peroxidation increased the rate of hydrolysis of soy PC liposomes that did not contain PE. In order to minimize
interfacial factors that may result in an increase in rate, the lipids were solubilized in Triton X-100. In mixtures of Triton
with soy PC in the absence of PE, peroxidation dramatically increased the rate of lipid hydrolysis. In addition, the rate
of hydrolysis of the unoxidizable lipid 1-palmitoyl-2-[1-14C]oleoyl PC incorporated into PC/PE liposomes was unaffected by peroxidation of the host lipid. These data are consistent
with the notions that the increase in rate of hydrolysis of peroxidized PC substrates catalyzed by phospholipase A2 is due largely to a preference for peroxidized phospholipid molecules as substrates and that peroxidation of host lipid does
not significantly increase the rate of hydrolysis of nonoxidized lipids. 相似文献
7.
Freshly isolated rat hepatocytes were incubated for 20 min with [U-14C]glycerol in the presence or absence of unlabeled linoleic (18∶2n-6), arachidonic (20∶4n-6), or docosahexaenoic (22∶6n-3)
acid, added as albumin complex in 10% ethanol. Most of the radioactivity (≈95%) recovered in hepatocyte lipids was present
in phosphatidylcholine (PC), phosphatidylethanolamine (PF), and triacylglycerol (TAG). The presence of exogenous fatty acids
resulted in (i) higher incorporation of [U-14C]glycerol, (ii) higher percentage of label in TAG, and (iii) enhanced formation of PC and PE molecular species bearing the
exogenous fatty acid at both the sn-1 and sn-2 positions of glycerol. In each case, these molecular species contained 60 to 70% of the label in that lipid class. Further
incubation of the cells for 40 and 80 min in the absence of labeled substrate and exogenous fatty acids resulted in a redistribution
of label among PC and PE molecular species due to deacylation-reacylation at the sn-1 position of glycerol. 相似文献
8.
This paper presents the positional distribution of fatty acids in triacyl-sn-glycerols (TAG) of Artemia nauplii used in aquaculture as a live food for marine fish larvae. The nauplii were enriched with docosahexaenoic acid (DHA)
ethyl ester (EE) in the form of gelatin-acacia microcapsules for 4, 18, and 24 h. TAG of the initial, enriched, and unenriched
Artemia nauplii were subjected to stereospecific analysis. A remarkable increase of DHA content in the enriched Artemia TAG confirmed the view that DHA-EE is effectively assimilated and incorporated into the TAG fraction of Artemia nauplii. TAG of the nauplii enriched with 25 mg/L of DHA-EE contained DHA at concentrations of 5.9–6.8, 4.3–6.0, and 14.3–22.3
mol% in the sn-1, sn-2, and sn-3 positions, respectively. When the nauplii were enriched with 100 mg/L of DHA-EE, proportions of DHA in the sn-1, sn-2, and sn-3 positions were 5.2–8.6, 3.9–6.0, and 12.2–25.4 mol%, respectively. In all of the enriched Artemia, DHA was preferentially located in the sn-3 position followed in sequence by the sn-1 and sn-2 positions. The lower content of DHA in the sn-1 and sn-2 positions was consistent with low content of this acid in 1,2-diacyl-sn-glycerophospholipids. When fish larvae are reared on Artemia nauplii enriched with LL-type DHA oil, the larvae feed on DHA esterified in TAG with a positional distribution pattern similar
to that of marine mammals (sn-3≫sn-1>sn-2) rather than that of fish or marine invertebrates (sn-2≫sn-3>sn-1). 相似文献
9.
The sn-position of FA in membrane lipids has an influence on the physiological function of cells, is predictive for diseases, and
therefore is useful for diagnostics. The current study compares the compositions of acyl chain substituents in the sn-1 and sn-2 positions of the glycerol backbones of phospholipids derived from human erythrocytes by using RP-HPLC coupled with on-line
electrospray ionization ion trap MS. Preferential loss of the acyl group in the sn-1 position was used to determine the degree of regiospecific preference exhibited by the phospholipid molecules. The identities
of the molecular species and the positions of the acyl substituents were identified using product-ion spectra of major precursor
ions selected from the mass spectra averaged across peaks in the total ion chromatogram. Saturated FA were found to be located
mainly in the sn-1 position of the glycerol backbones of erythrocyte phospholipids, whereas PUFA were found primarily in the sn-2 position. All measured phospholipids revealed palmitic acid (16∶0) at the sn-1 position. Linoleic acid (18∶2n−6) and arachidonic acid (20∶4n−6) were found to be attached exclusively to the sn-2 position of the backbone, whereas eicosadienoic (20∶2n−6) and eicosatrienoic acid (20∶3n−9) occurred in both positions
of the backbone of PC. Oleic (18∶1n−9), linoleic (18∶2n−6), and octadecatrienoic (18∶3) acids of PE and PS were linked to
both positions. Lignoceric acid (24∶1n−9) was found to be strictly localized at the sn-2 position, whereas nervonic (24∶1n−9) acid of PS was associated with both positions of the backbone. A detailed analysis
of the blood cell membrane lipids by MS might be helpful to characterize postprandial kinetics of pharmacological or dietary
lipid applications, as well as environmental influences on cell membranes. 相似文献
10.
As part of a program to elucidate castor oil biosynthesis, we have identified 36 molecular species of PC and 35 molecular
species of PE isolated from castor microsomes after incubations with [14C]-labeled FA. The six [14C]FA studied were ricinoleate, stearate, oleate, linoleate, linolenate, and palmitate, which were the only FA identified in
castor microsomal incubations. The incorporation of each of the six FA into PC was better than that into PE. The [14C]FA were incorporated almost exclusively into the sn-2 position of both PC and PE. The incorporation of [14C]stearate and [14C]palmitate into 2-acyl-PC was slower compared to the other four [14C]FA. The incorporation does not show any selectivity for the various lysoPC molecular species. The level of incorporation of [14C]FA in PC was in the order of: oleate>linolenate>palmitate>linoleate >stearate>ricinoleate, and in PE: linoleate>linolenate>
oleate>palmitate>stearate>ricinoleate. In general, at the sn-1 position of both PC and PE, linoleate was the most abundant FA, palmitate was the next, and oleate, linolenate, stearate,
and ricinoleate were minor FA. The activities of oleoyl-12-hydroxylase, oleoyl-12-desaturase seem unaffected by the FA at
the sn-1 position of 2-oleoyl-PC. The FA in the sn-1 position of PC does not significantly affect the activity of phospholipase A2, whereas ricinoleate is preferentially removed from the sn-2 position of PC. The results show that (i) [14C]oleate is most actively incorporated to form 2-oleoyl-PC, the immediate substrate of oleoyl-12-hydroxylase; (ii) 2-ricinoleoyl-PC
is formed mostly by the hydroxylation of 2-oleoyl-PC, not from the incorporation of ricinoleate into 2-ricinoleoyl-PC; and
(iii) 2-oleoyl-PF is less actively formed than 2-oleoyl-PC. 相似文献
11.
A. C. Lanser 《Lipids》1982,17(8):524-528
The deposition oftrans-8-octadecenoate-8(9)-3H (8t-18∶1-3H) was compared tocis-9-octadecenoate-10-14C (9c-18∶1-14C) in the major egg yolk neutral lipids and phospholipids and in organ lipids from the laying hen.trans-8-Octadecenoate was preferentially incorporated into only the phosphatidylethanolamines (PE), whereas discrimination against
8t-18∶1-3H occurred in the phosphatidylcholines (PC), triglycerides (TG) and cholesteryl esters (CE). The 1-acyl position of both PE
and PC contained three times more 8t-18∶1-3H than 9c-18∶1-14C. Almost total exclusion of the 8t-18∶1-3H from the 2-acyl position of these phospholipids was found. Preferential incorporation of 9c-18∶1-14C occurred at the combined 1- and 3-acyl positions and at the 2-acyl position of yolk TG. Tissue lipid analyses indicated
that there was preferential deposition of 9c-18∶1-14C into all organs. Individual liver lipid classes displayed the same relative order of discrimination against 8t-18∶1-3H as did egg yolk lipids (CE>TG>PC>PE). 相似文献
12.
Yasuhiro Ando Toru Ota Yukiko Matsuhira Kazunaga Yazawa 《Journal of the American Oil Chemists' Society》1996,73(4):483-487
This paper presents the positional distribution of fatty acids in docosahexaenoic acid (22∶6n-3)-rich fish oil triacyl-sn-glycerols (TG). Stereospecific analysis of TG was carried out by a nonenzymatic method. The TG of bonito head oil, obtained
after a winterization process, contained 22∶6n-3 at concentrations of 28,7, and 49 mole % in thesn-1,sn-2, andsn-3 positions, respectively. In the TG of oil before the winterization process, 22∶6n-3 was concentrated in thesn-3 position, followed evenly by thesn-1 andsn-2 positions. Tuna orbital oil, obtained after winterization, showed the preferential association of 22∶6n-3 to thesn-3 position, followed by thesn-1 position. This distribution pattern was similar to that observed for seal oil TG rather than sardine oil TG. The bonito
head and tuna orbital oils are useful as fish oils with characteristics different from those of common fish oils, such as
menhaden, sardine, and herring oils. 相似文献
13.
Erick Reyes Suárez Paul F. Mugford Alfred J. Rolle Ian W. Burton John A. Walter Jaroslav A. Kralovec 《Journal of the American Oil Chemists' Society》2010,87(12):1425-1433
The regio-isomeric distribution of the omega-3 polyunsaturated fatty acids (PUFA) cis-5,8,11,14,17-eicosapentaenoic acid (EPA) and cis-4,7,10,13,16,19-docosahexaenoic acid (DHA) in the triacylglycerols (TAG) of anchovy/sardine fish oil was determined by 13C nuclear magnetic resonance (NMR) analysis under quantitative conditions. From the measurements of sn-1,3 and sn-2 carbonyl peak areas it was established that EPA was mainly located in the sn-1,3 positions, whereas DHA primarily occupied the sn-2 position. Reconstituted TAG prepared by Candida antarctica lipase-B (CALB) glycerolysis of the ethyl ester (EE) or the free fatty acid (FFA) forms of anchovy/sardine fish oil, displayed
a different pattern: EPA was equally distributed, while DHA was preferentially attached to the sn-1,3 positions. TAG concentrates of varying EPA and DHA molar fractions were prepared by CALB-catalyzed glycerolysis of the
corresponding EE and FFA. 13C-NMR analysis of the purified products revealed a lack of CALB regioselectivity for EPA and a slight sn-1,3 regioselectivity for DHA. Since this pattern was observed in all cases of this study, it was concluded that the lipase
regioselectivity during TAG synthesis is independent of both the acyl donor type (carboxylic acid or ester) and the fatty
acid content of the oil substrate. 相似文献
14.
For the purpose of characterizing the effect of starvation on 22∶6n−3 (DHA) content in marine fish tissues, horse mackerel
(Trachurus japonicus) were reared in a tank containing filtered, sterilized seawater under nonfeeding conditions for 107 d (survival rate of the
fish was 96.5%). The crude total lipids (TL) of ordinary dorsal muscle, dorsal skin, and viscera of the starved individuals
were separated into classes on silicic acid columns, and the constituents of the TL were quantified by gravimetric recovery
from column chromatography. The TL, initially>85% TAG in dorsal muscle, and even more in skin lipids, decreased dramatically
within the first 44 d of starvation, and then decreased more gradually during the remainder of the test period, whereas the
visceral TL decreased more slowly. The percentages of both saturated and monoenoic FA in the muscle TL also decreased somewhat,
but those of DHA increased significantly in muscle during the test periods. Decreases in PE and PC initially were much smaller
than TAG, but DHA levels remained high in both PE and PC. These findings indicate that all of the FA in the depot lipids of
horse mackerel tissues are easily metabolized for energy production during starvation, but DHA in muscle lipids of the starved
fish was maintained at a consistently high level, indicating that starvation did not affect DHA stability in phospholipids.
The findings suggest that preservation of DHA in cell membrane lipid PE and PC is necessary for self-protection functions
in starving fish. 相似文献
15.
Preparation of Infant Formula Fat Analog Containing Capric Acid and Enriched with DHA and ARA at the sn-2 Position
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An infant formula fat analog with capric acid mostly esterified at the sn‐1,3 positions, and substantial amounts of palmitic, docosahexaenoic (DHA), and arachidonic (ARA) acids at the sn‐2 position, was prepared by physically blending enzymatically synthesized structured lipids (SL) with vegetable oils. The components of the blend included high sn‐2 palmitic acid SL enriched with capric acid (SLCA), canola oil (CAO), corn oil (CO), high sn‐2 DHA (DHAOm), and high sn‐2 ARA (ARAOm) enzymatically modified oils. Each component was proportionally blended to match the fatty acid profile of commercial fat blends used for infant formula. The infant formula fat analog (IFFA1) was characterized for total and positional fatty acids (FA), triacylglycerol (TAG) molecular species, thermal behavior, and tocopherol content. IFFA1 contained 17.37 mol% total palmitic acid of which nearly 35 % was located at the sn‐2 position. The total capric acid content was 13.93 mol%. The content of DHA and ARA were 0.49 mol% (48.18 % at sn‐2) and 0.57 mol% (35.80 % at sn‐2), respectively. The predominant TAG were OPO (24.09 %), POP (15.70 %), OOO (11.53 %), and CLC (7.79 %). The melting completion and crystallization onset temperatures were 18.65 and ?2.19 °C, respectively. The total tocopherol content was 566.45 μg/g. This product might be suitable for commercial production of infant formulas. 相似文献
16.
Iron-catalyzed lipid peroxidation was examined using 1H NMR in a biphasic aqueous-chloroform system. At physiological pH (7.4), mole ratios of phospholipids/Fe3+ as low as 1300∶1 catalyzed the rapid disappearance of endogenous lipid hydroperoxides with a loss of two of the four double
bonds in PC containing palmitic (16∶0) and arachidonic (20∶4) acids in the sn-1 and sn-2 positions, respectively. The predominant phospholipid products after 1 h at 20°C were a 9-carbon monounsaturated carbonyl
and a phospholipid with an 11-carbon Δ5,8 FA in the sn-2 position. PC with linoleic acid (18∶2) in the sn-2 position lost one double bond and formed a phospholipid with a 9-carbon FA. Cardiolipin (linoleic acid-rich) also lost
about 40% of its double bonds. No detectable loss was seen for PC containing oleic acid (18∶1) or neutral lipids with PUFA.
At arachidonyl PC/Fe3+ ratios less than 20∶1, significant broadening of the choline methyl proton peak was evident, indicating that Fe3+ may form a complex with the adjacent phosphate group and that the complex involves both the phosphate and the hydroperoxide
adjacent to the Δ11 double bond. The results demonstrate that, at physiological pH, Fe3+-catalyzed peroxidation in polyunsaturated phospholipids occurs selectively adjacent to specific double bonds (Δ9 or Δ11). These PC-derived products have been shown to activate components of the inflammatory system. This suggests that the episodic
release of ferric ions may play a significant role in generating inflammatory mediators. 相似文献
17.
TG containing stearic acid,synthesized from coconut oil,exhibit lipidemic effects in rats similar to those of cocoa butter 总被引:1,自引:0,他引:1
Lipase-catalyzed interesterification was used to prepare structured TG from coconut oil TG by partially replacing some of
the atherogenic saturated FA with stearic acid, which is known to have a neutral effect on lipid levels in the body. The level
of stearic acid was increased from 4% in the native coconut oil to 40% in the structured lipids, with most of the stearic
acid being incorporated into the sn−1 and sn−3 positions of TG. When structured lipids were fed to rats at a 10% level for a period of 60 d, a 15% decrease in total cholesterol
and a 23% decrease in LDL cholesterol levels in the serum were observed when compared to those fed coconut oil. Similarly,
the total and free cholesterol levels in the livers of the rats fed structured lipids were lowered by 31 and 36%, respectively,
when compared to those fed coconut oil. The TG levels in the serum and in the liver showed decreases of 14 and 30%, respectively,
in animals fed structured lipids. Rats fed cocoa butter and structured lipids having a similar amount of stearic acid had
similar lipid levels in the serum and liver. These studies indicated that the atherogenic potential of coconut oil lipids
can be reduced significantly by enriching them with stearic acid. This also changed the physical properties of coconut oil
closer to those of cocoa butter as determined by DSC. 相似文献
18.
Ian C. Chandler 《Journal of the American Oil Chemists' Society》2001,78(7):737-742
Lipase regioselectivity is the ability to distinguish between primary (i.e., sn-1,3) and secondary (sn-2) ester functionalities in a triacylglycerol molecule, which is of importance in the manufacture of structured lipids. Unlike
existing methods of assessment, which utilize hydrolysis reactions, an alternative technique to assess the regioselectivity
of lipases in triacylglycerol transesterification reactions has been developed. An acidolysis reaction is performed between
triolein and decanoic, lauric, or stearic acids under conditions that minimize acyl migration, and products are analyzed by
silver-ion complexation liquid chromatography, enabling detection of specific triacylglycerol positional isomers. From the
rate of formation of these isomers the relative selectivity of the lipase for sn-2 and sn-1,3 ester bonds is determined. With lipases known to lack regioselectivity, the rate of reaction at sn-2 was similar to that at sn-1,3 from the start of the reaction. With sn-1,3 selective lipases, the formation of triacylglycerol isomers with decanoic acid in the secondary position was not detected
at any point in the reaction. Regioselectivity as a function of reaction progress was monitored. Two lipases from the genus
Pseudomonas exhibited activity toward all positions, but the rate at sn-2 was much reduced, and no incorporation of decanoic acid into this position was detectable until a high degree of conversion
had been achieved. 相似文献
19.
Naturally occurring tetraalkylsubstituted furan fatty acids (F-acids) were tested as potential substrates for soybean lipoxygenase-1.
For this purpose, F-acid methyl ester and phosphatidylcholines containing F-acids at thesn-2 position of the glycerol residue wer incubated with the enzyme. Oxidation of F-acids only occurs in the presence of linoleic
acid as co-substrate. Linoleic acid is converted by lipoxygenase to the corresponding hydroperoxide that oxidizes the F-acid,
probably in a radical reaction, to form an unstable dioxoene compound. This intermediate the forms, dependent on pH, unsaturated
furanoid acids or isomers with cyclopentenolone structure that can be detected by gas chromatography/mass spectrometry (GC/MS).
F-acids located at thesn-2 position of a synthetic phosphadidylcholine (PC), containing linoleic acid in thesn-1 position, are co-oxidized to a greater extent by incubation with soybean lipoxygenase-1 than are F-acids bound to PC with
myristic acid in thesn-1 position when subjected to the enzyme in the presence of a great excess of linoleic acid. The results suggest that F-acids
may play a strategic role in antioxidative processes in plant cells. 相似文献
20.
Rebecca W. Wilcox Tom Thuren Patricia Sisson Gregory L. Kucera Moseley Waite 《Lipids》1991,26(4):283-288
Rat hepatic lipase, an enzyme whose involvement in the catabolism of lipoproteins remains poorly defined, has both neutral
lipid and phospholipid hydrolyzing activity. We determined the substrate specificity of hepatic lipase for 1-oleoyl-sn-glycerol, 1,2-dioleoyl-sn-glycerol, and 1,3-dioleoyl-sn-glycerol in the Triton X-100 mixed micellar state, and compared these results to those obtained previously in our laboratory
for the phospholipid substrates phosphatidic acid (PA), phosphatidylethanolamine (PE), and phosphatidylcholine (PC). Vmax values were determined by diluting the substrate concentration in the surface of the micelle by Triton X-100. The Vmax values obtained were 144 μmol/min/mg for 1-oleoyl-sn-glycerol, 163 μmol/min/mg for 1,2-dioleoyl-sn-glycerol, and 145 μmol/min/mg for 1,3-dioleoyl-sn-glycerol. These values were higher than those obtained earlier for phospholipids which were 67 μmol/min/mg for PA, 50 μmol/min/mg
for PE and 4 μmol/min/mg for PC. In addition, the mole fraction of lipid substrate at half maximal velocity (K) in the surface
dilution plot was lower for the neutral lipid substrates as compared to those obtained for the phospholipid substrates. When
the hydrolysis of 1,3-dioleoyl-sn-glycerol mixed micelles was studied as a function of time, cleavage at thesn-1 andsn-3 positions occurred at the same rate, suggesting that hepatic lipase is not stereo-selective with respect to 1,3-diacyl-sn-glycerol substrates. To determine if the presence of one lipid could affect the hydrolysis of the other, all possible dual
combinations of 1-oleoyl-sn-glycerol, 1,2-dioleoyl-sn-glycerol, and 1,3-dioleoyl-sn-glycerol, in the same micelle were made and the hydrolysis rate of each substrate was determined. Interaction occurred only
for the 1,2-dioleoyl-sn-glycerol/1,3-dioleoyl-sn-glycerol mixture where the hydrolysis of 1,2-dioleoyl-sn-glycerol was slightly inhibited and that of 1,3-dioleoyl-sn-glycerol slightly activated compared to the predicted theoretical rate. These findings demonstrate that when presented in
similar physical states, the neutral lipid substrates tested were hydrolyzed at a higher rate by hepatic lipase than the phospholipid
substrates. 相似文献