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1.
The conversion of 2-acyl-sn-glycero-3-phosphorylinositol into phosphatidylinositol via acyl-CoA: 2-acyl-sn-glycero-3-phosphorylinositol acyltransferase activity was found to occur in rat liver microsomes. Over a wide range of conditions,
stearic acid was preferred over palmitate by the acyltransferase when these acids were presented in mixtures as acyl-CoA derivatives.
The potential importance of this enzyme activity for the entry of stearic acid into the 1-position of hepatic phosphatidylinositol
is further supported by its greater preference for stearate relative to the acyl-CoA: 2-acyl-sn-glycero-3-phosphorylcholine acyltransferase under certain assay conditions. 相似文献
2.
B. J. Holub 《Lipids》1976,11(1):1-5
The conversion of 1-acyl-sn-glycero-3-phosphorylinositol-3H into phosphatidylinositol-3H was studied using rat liver microsomal and homogenate preparations. The nature of the molecular species of phosphatidyl
inositol so formed in the absence of added acyl moieties was determined after fractionating the radioactive product by means
of argentation thin layer chromatography. In other experiments, the possible specificity of the microsomal acyl-CoA:1-acyl-sn-glycero-3-phosphorylinositol acyltransferase towards different acyl-CoA derivatives was investigated. Maximum conversion
of 1-acyl GPI to the diacyl analogue was dependent on the addition of adenosine triphosphate and CoA when exogenous acyl groups
were omitted from the incubation medium. Under these latter conditions, the tetraenoic species comprised 56–74% of the total
molecular species of newly-formed phosphatidylinositol. The microsomal acyl-CoA:1-acyl-sn-glycero-3-phosphorylinositol acyltransferase showed a marked preference for arachidonoyl-CoA. The present results suggest
that the enrichment of rat liver phosphatidyl inositol in arachidonic acid may arise when 1-acyl-sn-glycero-3-phosphorylinositol is acylated to form phosphatidylinositol.
Presented in part at the AOCS Spring Meeting, Dallas, April, 1975. 相似文献
3.
Dietary manipulation produces marked alterations in desaturase activities of rat liver microsomes with no concomitant changes
in acyltransferase activities. Desaturation of stearoyl-CoA (Δ9-desaturase), linoleoyl-CoA (Δ6-desaturase), eicosatrienoyl-CoA
(Δ5-desaturase) and eicosatrienoyl-phosphatidylcholine (Δ5-desaturase) was elevated in animals fed a corn oil diet and lowered
in those fed a coconut oil diet compared to control animals. The Δ5-desaturase activities were also lowered in starved animals
and elevated in starved animals refed a fat-free diet. However, no changes in acyl-CoA:1-acylsn-glycero-3-phosphocholine acyltransferase activity were observed in the membranes of animals maintained on any of the dietary
regimens studied. These observations suggest that the desaturases of rat liver microsomes are regulated independently of the
acyltransferases and that desaturation of eicosatrienoyl-phosphatidylcholine is regulated at the level of the desaturase itself
and not by availability of the phospholipid substrate. 相似文献
4.
P. J. A. O'doherty 《Lipids》1979,14(1):84-87
The importance of the steric configuration of lysophosphatidylcholine in the lymphatic transport of fat was investigated in
bile fistula rats. It was found that the feeding of 1-palmitoyl-sn-glycero-3-phosphocholine increased the lymphatic output of phosphatidyl choline and triacylglycerol, while the feeding of
3-palmitoyl-sn-glycero-1-phosphocholine had no effect. In intestinal microsomes of the bile fistula rats, it was found that the lysophosphatidylcholine
acyltransferase was stereospecific in acylating the 1-acyl-sn-glycero-3-phosphocholine enantiomer. The significance of these findings is briefly discussed. 相似文献
5.
Acyl-acyl carrier protein (acyl-ACP) can serve as well as acyl-CoA as substrate of the 1-acyl-sn-glycero-3-phosphocholine (1-acyl-GPC) acyltransferase of rat-liver microsomes. The product of the acylation with either thioester
substrate is predominantly phosphatidylcholine (PC) (92–95%). The acyl-group transferred from either myristoyl-CoA or myristoyl-ACP
is located at the C-2 position of the phospholipid (PL). The apparent Km values for the myristoyl-CoA and myristoyl-ACP were
46 μM and 63 μM, and the corresponding apparent Vmax values were 1.0 and 1.6 nmol/min/mg. The rate of acylation with the acyl-ACP
was unaffected by the addition of free CoA-SH. These data suggest that acyl-CoA and acyl-ACP are transferred to 1-acyl-GPC
by the same or similar enzyme systems. 相似文献
6.
The metabolism of arachidonate in brain membrane phosphoglycerides was investigated in vivo by intracerebral injection of
labeled arachidonate and by in vitro assay of enzymic systems associated with the metabolism. After intracerebral injection,
labeled arachidonate was incorporated rapidly into brain phosphoglycerides with radioactivity distributed mainly in diacyl-sn-glycero-3-phosphoinositols (GPI) and diacyl-sn-glycero-3-phosphocholines (GPC). Some evidence of a metabolic relationship between diacyl-sn-glycerophosphoinositols (diacyl-GPI) and diacylglycerols was observed. Among the phosphoglycerides labeled with [14C] arachidonoyl groups, diacyl-GPI were most rapidly metabolized in brain microsomal and synaptosomal fractions. The decay
of diacyl-GPI in brain synaptosomes may be represented by two pools with half-lives of 5 hr and 5 days. Three types of enzymic
systems related to metabolism of the polyunsaturated fatty acids in brain were investigated. The first system involves the
cyclic events relating the ATP-dependent activation of polyunsaturated fatty acids (PUFA) to their acylCoA by the acylCoA
ligase and subsequent hydrolysis of acylCoA to free fatty acids by the acylCoA hydrolase. It is apparent that fatty acid activation
and hydrolysis is under strigent control in order to maitain suitable levels of free fatty acids and acylCoA in the brain
tissue for various metabolic use. Factors involved in the regulation may include the level of ATP, divalent cations and the
nature of substrates. The second enzymic system pertains to deacylation via phospholipase A2 and reacylation via the acyltransferase of membrane phosphoglycerides. In brain tissue, activity of the acyl transferase
is generally higher than that of the phospholipase A2. Factors known to affect specificity of the acyltransferase include substrate concentration and the nature of the acyl groups
and lysophosphoglycerides. The acyltranferase(s) in brain preferentially transfers arachidonate to 1-acyl-GPI. Activity of
the acyltransferase can be inhited by a number of lypophilic compounds including local anesthetics and cell surface agents.
Activity of the phospholipase A2 in brain may depend on the physical form of the substrates, i.e., whether the substrates are in monomeric or micellar form.
The third process is associated with the degradation of diacyl-GPI by enzymes present in brain subcellular membranes. Incubation
of brain subcellular membranes with 1-acyl-2-[14C] arachidonoyl-GPI yielded labeled diacylglycerols and arachidonate. The phospholipase C action is specific for hydrolysis
of diacyl-GPI. The arachidonate released from incubation of labeled diacyl-GPI may be the result of phospholipase A2 action which is not specific for diacyl-GPI or the hydrolysis by lipase acting on the diacylglycerols formed from the phospholipase
C activity. Enzymic hydrolysis of diacyl-GPI is most active in the microsomal fraction, but uoon disruption of synaptosomes,
enzyme in synaptic plasma membranes is also active in degradating this glycerophospholipid. In general, the results of in
vitro studies are in good agreement with those observed in vivo and the information yielded has contributed towards understanding
the metabolism of polyunsaturated fatty acids in brain subcellular membranes. 相似文献
7.
Resolution of individual molecular species of human platelet 1,2-diradyl-sn-glycero-3-phosphocholines and 1,2-diradyl-sn-glycero-3-phosphoethanolamines by reverse phase high pressure liquid chromatography (HPLC) allowed a thorough analysis of
those phospholipids labeled with [3H]arachidonic acid. Approximately 54% and 16% of the total incorporated radiolabel was found in choline glycerophospholipids
and ethanolamine glycerophospholipids, respectively, with ca. 90% of this being found in the 1,2-diacyl molecular species.
Eighty percent of [3H]-arachidonic acid incorporated into 1-acyl-2-arachidonoyl-sn-glycero-3-phosphocholine in resting platelets was equally distributed between 1-palmitoyl-2-arachidonoyl and 2-stearoyl-2-arachidonoyl-sn-glycero-3-phosphocholine, while 70% of the radiolabel in 1-acyl-2-arachidonoyl-sn-glycero-3-phosphoethanolamine was found in 1-stearoyl-2-arachidonoyl-sn-glycero-3-phosphoethanolamine. Thrombin stimulation (5 U/ml for 5 min) resulted in deacylation of all 1-acyl-2-[3H]arachidonoyl molecular species of 1-acyl-2-arachidonoyl-sn-glycero-3-phosphocholine and 1-acyl-2-arachidonoyl-sn-glycero-3-ethanolamine. There was also a slight increase in 1-O-alkyl-2-[3H]arachidonoyl-sn-glycero-3-phosphocholine and a significant increase in 1-O-alk-1′-enyl-2-[3H]arachidonoyl-sn-glycero-3-phosphoethanolamine molecular species of over 300%. Thus, HPLC methodology indicates that arachidonoyl-containing
molecular species of phosphatidylcholine and phosphatidylethanolamine are the major source of arachidonic acid in thrombin-stimulated
human platelets, while certain ether phospholipid molecular species become enriched in arachidonate. 相似文献
8.
Jen-sie Tou 《Lipids》1987,22(5):333-337
The present study showed that platelet-activating factor (1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine, PAF), but not lysoPAF (1-O-hexadecyl-sn-glycero-3-phosphocholine) rapidly (within 15 sec) stimulated the incorporation of both [1-14C]arachidonate and [1-14C]docosahexaenoate into phosphatidylinositol (PI) and phosphatidylcholine (PC) in human neutrophils. Concomitantly, it inhibited
the formation of labeled phosphatidic acid from both fatty acids. The magnitude of stimulation (percentage of control) was
greater in PI than in PC for the incorporation of arachidonate and vice versa for the incorporation of docosahexaenoate. It
reached a maximum at 10−7 M and started to decline at 10−6 M. Extracellular Ca2+ was not essential for the action of PAF on phospholipid acylation. The distribution of labeled arachidonate in the molecular
species of PC was not altered by PAF after 1 min incubation, suggesting that the increased formation of arachidonyl-PC during
the early stage of neutrophil-PAF interaction was not originated from the added PAF. No measurable changes in the mass of
each phospholipid were detected in neutrophils challenged by PAF from 15 sec to 2 min. The data suggest that the increased
incorporated of extracellular fatty acids into PI and PC elicited by PAF may be secondary to increased deacylation of these
phospholipids, and the magnitude of stimulation reflects the specificity of acyltransferase catalyzing the acylation of lysoPI
and lysoPC by fatty acyl-CoA. 相似文献
9.
In pericytes from bovine retina, the enzyme glycerophosphocholine phosphodiesterase, catalyzing the hydrolysis of sn-glycero-3-phosphocholine to glycero-3-phosphate and choline, has been characterized with respect to pH optimum, metal ion
dependence, K
m, inhibitors, and subcellular localization. In these cells, the natural substrate sn-glycero-3-phosphocholine was present at relatively high concentration (6.4±1.2 nmol/mg protein), and the EDTA-sensitive phosphodiesterase
activity was also found to be markedly high (9.80±1.5 nmol/min/mg protein) compared to the estimated in liver and brain (1–3
nmol/min/mg protein) or in renal epithelial cell culture (0.27 nmol/min/mg protein). The reaction conditions were in general
agreement with those found earlier in brain and other tissues. The majority of the enzyme specific activity was located in
the plasma membrane, whereas a minor part was present in the microsomal fraction. The physiological significance of the high
catabolic phosphodiesterase activity in these cells may be related to the tranfer, followed by deacylation, of lysophosphatidylcholine
from the bloodstream to nervous tissue. In addition, capillary pericytes in culture were able to incorporate 3H-choline rapidly into choline-containing soluble phosphorylated intermediates and into phosphatidylcholine. To find a positive
and negative effector on phosphatidylcholine formation, adenosine, an important intercellular mediator in the retina in response
to alterations in oxygen delivery, and endothelin-1, a potent paracrine mediator present at the blood-brain and blood-retina
barrier, were tested. The cells cultured for 1 or 24 h in a medium containing adenosine at concentrations of 10−6 and 10−4 M showed significant reduction in 3H-choline incorporation compared to control cultures, whereas endothelin-1, at a concentration of 10 and 100 nM, caused stimulation
of phosphatidylcholine biosynthesis. These findings provide evidence that both agonists may modulate phosphatidylcholine metabolism
in pericytes. 相似文献
10.
Acetyl-CoA:1-alkyl-2-lyso-sn-glycero-3-phosphocholine (lyso-PAF) ultrasonic disruption in the presence of 25% glycerol from rat spleen microsomes. About
26% of the enzymatic activity was recovered in the 225,000×g supernatant by this treatment, although the specific activity
was slightly decreased compared with the original microsomes. The solubilized enzyme was remarkably susceptible to various
kinds of metal ions. Sulfhydryl reagents such as p-chloromercuribenzoate and N-ethyl-maleimide significantly inhibited the
enzyme reaction, suggesting that the enzyme is an SH enzyme. Based on the sedimentation pattern in sucrose density centrifugation,
the isoelectric point, the kinetic characteristics and the sensitivity to tryptic digestion of microsomes, it appears that
acetyl-CoA:lyso-PAF acetyltransferase does not differ from the acetyltransferase responsible for the transfer of acetate from
acetyl-CoA to 1-acyl-2-lyso-sn-glycero-3-phosphocholine. 相似文献
11.
The concentration-dependent effects of two different synthetic phospholipids on cell proliferation and phosphatidylcholine
biosynthesis were compared in Madin-Darby canine kidney (MDCK) cells. The alkyllysophospholipid 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine and the alkylphosphocholine, hexadecylphosphocholine, inhibited cell proliferation with half-inhibitory
concentrations (IC50) of 75 and 135 μmol/L, respectively. The agents also inhibited phosphatidylcholine biosynthesis in confluent and proliferating
MDCK cells. The IC50 of 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine was 40 μmol/L in confluent cells and 20 μmol/L in proliferating cells, whereas the IC50 of hexadecylphosphocholine was higher in both experimental systems (67 μmol/L in confluent cells and 40 μmol/L in proliferating
cells). Further experiments revealed that the effect of both agents on phosphatidylcholine biosynthesis was reversible and
that the inhibition was mediated by translocation of the rate-limiting enzyme of this pathway, CTP: phosphocholine cytidylyltransferase
(EC 2.7.7.15), from membranes to the cytosol, where it is inactive. The present findings suggest that the inhibition of phosphatidylcholine
biosynthesis by both synthetic phospholipids might be related, in part, to their antiproliferative effects. 相似文献
12.
J. E. Kinsella 《Lipids》1972,7(5):349-355
The stearyl desaturase of lactating bovine mammary tissue is located in the microsomes and requires activated fatty acid and
NADH for activity. Other enzymes, acyl-transferase(s) and deacylase which apparently compete with the desaturase for substrate
are also present. Both the substrate 1-14C-stearyl CoA and the oleic acid produced by desaturase are esterified into the various lipid classes. The oleic acid is preferentially
acylated into positionsn-3 of the triglycerides andsn-2 of the phosphatidylcholine. Experimental conditions causing reduced desaturase activity depressed triglyceride synthesis,
and stimulation of desaturation by NADH L−α GP, acidic pH, 5.6, was accompanied by increased incorporation of radioactive fatty acids into the triglycerides. These data
indicated that desaturase and glyceride acyl transferase were located contiguously within the microsomal membranes. The possibility
that desaturase activity might control triglyceride synthesis in vivo is discussed. It was observed that mammary tissue from
nonlactating cows 1–2 weeks and 2 days prior to calving lacked or possessed very low stearyl desaturase activity. 相似文献
13.
Karli Lipinski Matthew J. McKay Fahmida Afrose Dr. Ashley N. Martfeld Prof. Roger E. Koeppe II Dr. Denise V. Greathouse 《Chembiochem : a European journal of chemical biology》2019,20(21):2784-2792
Membrane proteins are essential for many cell processes yet are more difficult to investigate than soluble proteins. Charged residues often contribute significantly to membrane protein function. Model peptides such as GWALP23 (acetyl-GGALW5LAL8LALALAL16ALW19LAGA-amide) can be used to characterize the influence of specific residues on transmembrane protein domains. We have substituted R8 and R16 in GWALP23 in place of L8 and L16, equidistant from the peptide center, and incorporated specific 2H-labeled alanine residues within the central sequence for detection by solid-state 2H NMR spectroscopy. The resulting pattern of [2H]Ala quadrupolar splitting (Δνq) magnitudes indicates the core helix for R8,16GWALP23 is significantly tilted to give a similar transmembrane orientation in thinner bilayers with either saturated C12:0 or C14:0 acyl chains (1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) or 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)) or unsaturated C16:1 Δ9 cis acyl chains. In bilayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC; C18:1 Δ9 cis) multiple orientations are indicated, whereas in longer, unsaturated 1,2-dieicosenoyl-sn-glycero-3-phosphocholine (DEiPC; C20:1 Δ11 cis) bilayers, the R8,16GWALP23 helix adopts primarily a surface orientation. The inclusion of 10–20 mol % cholesterol in DOPC bilayers drives more of the R8,16GWALP23 helix population to the membrane surface, thereby allowing both charged arginines access to the interfacial lipid head groups. The results suggest that hydrophobic thickness and cholesterol content are more important than lipid saturation for the arginine peptide dynamics and helix orientation in lipid membranes. 相似文献
14.
Synthesis of ethanolamine phosphoglycerides (EPG) from labeled14C-phosphorylethanolamine (PE) and cytidine triphosphate (CTP) has been studied in vitro in particles and in soluble fractions
of chicken brain. The microsomal membranes can carry out this conversion, but supplementing the microsomes with an enzymic
fraction derived from the particle-free supernatant results in a noticeable increase of the rate of EPG synthesis. Mitochondria
are almost inactive, in this connection. The conversion of PE to lipid is very low, in no case exceeding 0.5–0.6%, even in
the presence of diacyl glycerols or 1-alkenyl 2-acyl glycerol. No stimulation occurs by supplementing the incubation system
with natural lipid acceptors, intermediates of lipid synthesis, energy-producing cofactors or monoacylsn-glycero-3-phosphorylethanolamine (GPE), monoacylsn-glycero-3-phosphorylcholine (GPC) and other lipid material. From these and other results, the conclusion is made that the
PE:CTP cytidylyltransferase (E.C. 2.7.7.14) must display very low activity in vitro, thus limiting the overall rate of synthesis
from PE. Diacyl GPE is the only lipid which has been found labeled after incubation with PE of the brain preparations. A small
synthesis of alkenyl acyl GPE takes place, only when PE is incubated with suitable concentrations of a plasmalogenic diglyceride. 相似文献
15.
Acyl-CoA:lysophosphatidylcholine acyltransferase (LPCAT; EC 2.3.1.23) catalyzes the acyl-CoA-dependent acylation of lysophosphatidylcholine
(LPC) to produce PC and CoA. LPCAT activity may affect the incorporation of fatty acyl moieties at the sn-2 position of PC where PUFA are formed and may indirectly influence seed TAG composition. LPCAT activity in microsomes prepared
from microspore-derived cell suspension cultures of oilseed rape (Brassica napus L. cv Jet Neuf) was assayed using [1-14C]acyl-CoA as the fatty acyl donor. LPCAT activity was optimal at neutral pH and 35°C, and was inhibited by 50% at a BSA concentration
of 3 mg mL−1. At acyl-CoA concentrations above 20 μM, LPCAT activity was more specific for oleoyl (18∶1)-CoA than stearoyl (18∶0)- and
palmitoyl (16∶0)-CoA. Lauroyl (12∶0)-CoA, however, was not an effective acyl donor. LPC species containing 12∶0, 16∶0, 18∶0,
or 18∶1 as the fatty acyl moiety all served as effective acyl acceptors for LPCAT, although 12∶0-LPC was somewhat less effective
as a substrate at lower concentrations. The failure of LPCAT to catalyze the incorporation of a 12∶0 moiety from acyl-CoA
into PC is consistent with the tendency of acyltransferases to discriminate against incorporation of this fatty acyl moiety
at the sn-2 position of TAG from the seed oil of transgenic B. napus expressing a medium-chain thioesterase. 相似文献
16.
Jiann-Tsyh Lin Thomas A. McKeon Marta Goodrich-Tanrikulu Allan E. Stafford 《Lipids》1996,31(6):571-577
We have characterized the oleoyl-12-hydroxylase in the microsomal fraction of immature castor bean using the putative substrate,
1-acyl-2-oleoyl-sn-glycero-3-phosphocholine (2-oleoyl-PC). Previous characterizations of this enzyme used oleoyl-CoA as substrate and relied
on the enzyme transferring oleate from oleoyl-CoA to lysophosphatidylcholine to form 2-oleoyl-PC (acyl-CoA:lysophosphatidylcholine
acyltransferase) in addition to oleoyl-12-hydroxylase. The present assay system and characterization use 2-oleoyl-PC as substrate
(oleoyl-12-hydroxylase alone). Use of the actual substrate for assay purposes is important for the eventual purification of
the oleoyl-12-hydroxylase. Ricinoleate (product of oleoyl-12-hydroxylase) and linoleate (product of oleoyl-12-desaturase)
were identified as metabolites of oleate of 2-oleoyl-PC by high-performance liquid chromatography and gas chromatography/mass
spectrometry. The activity of oleoyl-12-hydroxylase in the microsomal fraction reached a peak about 44 d after anthesis of
castor, while the activity of oleoyl-12-desaturase reached a peak about 23 d after anthesis. The optimal temperature for the
oleoyl-12-hydroxylase was about 22.5°C, and the optimal pH was 6.3. Catalase stimulated oleoyl-12-hydroxylase while bovine
serum albumin and CoA did not activate oleoyl-12-hydroxylase. The phosphatidylcholine analogue, oleoyloxyethyl phosphocholine,
inhibited the activity of oleoyl-12-hydroxylase. These results further support the hypothesis that the actual subtrate of
oleoyl-12-hydroxylase is 2-oleoyl-PC. 相似文献
17.
Preparation of phospholipids highly enriched with n-3 polyunsaturated fatty acids by lipase 总被引:3,自引:0,他引:3
Gudmundur G. Haraldsson Atli Thorarensen 《Journal of the American Oil Chemists' Society》1999,76(10):1143-1149
The immobilized 1,3-regiospecific Rhizomucor miehei lipase (Lipozyme™) was employed to catalyze the transesterification reaction (acidolysis) of 1,2-diacyl-sn-glycero-3-phosphatidylcholine with n-3 polyunsaturated fatty acids under nonaqueous solvent-free conditions. With a concentrate
of 55% eicosapentaenoic acid (EPA) and 30% docosahexaenoic acid (DHA) and pure phosphatidylcholine from egg yolk, phospholipids
of 32% EPA and 16% DHA content were obtained, presumably as a mixture of phosphatidylcholine and lysophosphatidylcholine.
31P nuclear magnetic resonance (NMR) analysis turned out to be a valuable technique to study the details of the reactions involved.
It revealed that when 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine was transesterified with 98% pure EPA, a substantial amount of hydrolysis side reaction took
place (39%), leading to a product mixture of 39% phosphatidylcholine, 44% lysophosphatidylcholine, and 17% sn-glycerol-3-phosphatidylcholine. The lysophosphatidylcholine constituent comprised 70% EPA, whereas the phosphatidylcholine
component contained 58% EPA. The 31P NMR technique provided valid information about the mechanism of the reaction. It became evident that a high dosage of lipase
containing 5% water afforded optimal conditions for the optimal extent of EPA incorporation into the phospholipids, under
which the extent of hydrolysis side reaction remained relatively high. 相似文献
18.
Saccharomyces cerevisiae cells were demonstrated to contain lysophosphatidylcholine (lysoPtdCho) acyltransferase (E.C. 2.3.1.23) activity. The enzyme
displayed K
m(app) of 69 μM for lysoPtdCho and 152 μM for oleoyl CoA. Enzyme activity was not affected by the addition of 1 mM Mg2+, Mn2+, Ca2−, or 200 mM EDTA. However, Zn2+ inhibited lysoPtdCho acyltransferase activity to 33% control values at 0.1 mM and to 7% at 1.0 mM Zn2+. To further explore the possibility that lysoPtdCho acyltransferase may contain a high-affinity Zn2+ binding site, we tested the strong Zn2+ chelator o-phenanthroline for its ability to inhibit enzyme activity. LysoptdCho acyltransferase activity was inhibited to 18 and 27%,
respectively, those of control values in the presence of 2 and 1 mM o-phenanthroline, implying that a high-affinity Zn2+ binding site exists in lysoPtdCho acyltransferase or in an accessory protein that is essential for protein stability and/or
activity. Saccharomyces cerevisiae lysoPtdCho acyltransferase activity displayed a broad lysoPtdCho fatty acyl chain substrate specificity utilizing lysoPtdCho
molecules ranging in length from C10−C20 (the entire range tested). In addition, the enzyme was capable of using the ether-linked analog of lysoPtdCho, 1-O-alkyl-2-hydroxy-sn-3-glycerophosphocholine, as a substrate. The ability of S. cerevisiae to incorporate radiolabeled 1-O-alkyl-2-hydroxy-sn-3-glycerophosphocholine into phosphatidylcholine in vitro was exploited to demonstrate a direct precursor-product relationship between lysoPtdCho molecules and their incorportation
into phosphatidylcholine in vivo. Identical labeling results were obtained in S. cerevisiae cells disrupted for their major transacylase activity, PLB1, demonstrating that the incorporation of lysolipid was via acyltransferase, and not transacylase, activity. 相似文献
19.
Leslie S. Ramsammy Brenda Haynes Christine Josepovitz George J. Kaloyanides 《Lipids》1993,28(5):433-439
The purpose of this study was to investigate the roles of decreased synthesis and increased consumption in the depression
of arachidonic acid levels in renal cortex and glomeruli of rats with streptozotocin-induced diabetes mellitus. In diabetic
rats, arachidonic acid was depressed 33.2% in renal cortex, 47.4% in liver and 66.1% in heart compared to values of control
rats. Δ6 Desaturase activity was depressed in renal cortex, liver and heart of diabetic rats to 53.3, 55.5 and 63.7%, respectively,
of control values. Δ5 Desaturase activity was also depressed 43.7, 55.5 and 47.6% in renal cortex, liver and heart of diabetic
rats, respectively. In other rats the activities of five enzymes involved in the synthesis and esterification of arachidonic
acid were measured in renal cortex and in isolated glomeruli. Both tissues from diabetic rats showed depressed activities
of Δ5 and Δ6 desaturases, increased activities of long-chain acyl-CoA synthetase and 1-acyl-sn-glycero-3-phosphocholine acyltransferase and no change in the activity of elongase as compared to those in control tissues.
Malondialdehyde, an end product of lipid peroxidation, was lower in the renal cortex of diabetic rats than in control rats,
whereas β-oxidation of linoleic acid and arachidonic acid were similar in diabetic and in control rats. Basal and stimulated
prostaglandin E2 synthesis were significantly higher in isolated glomeruli from diabetic rats compared to those in control rats. In isolated
tubules, prostaglandin E2 synthesis was similarly low in both groups. From these data we conclude that the reduced level of arachidonic acid esterified
in lipids of the kidney cortex is caused principally by depressed synthesis of arachidonic acid secondary to decreased activity
of Δ5 and Δ6 desaturases. Increased consumption of arachidonic acid to support prostaglandin synthesis may have contributed
to the depression of arachidonic acid in glomeruli but not in tubules. 相似文献
20.
Δ9-tetrahydrocannabinol (THC) and merthiolate have been utilized as lysophospholipid acyltransferase inhibitors in metabolic
studies. However, their effects on acyltransferases other than lysophosphatidylcholine:acyl-CoA acyltransferase (LPCAT) are
not known. We have therefore investigated the effectiveness of THC and merthiolate in inhibiting the acylation of lysophosphatidylcholine,
lysophosphatidylethanolamine, lysophosphatidylserine, lysophosphatidylinositol (LPI) and lysophosphatidic acid (LPA) in guinea
pig liver microsomes using oleoyl-CoA and arachidonoyl-CoA as acyl donors. THC inhibited LPCAT and lysophosphatidylethanolamine:
acyl-CoA acyltransferase (LPEAT) by 40–50%, but had no effect or only slightly increased the activities of the other acyltransferases
when assayed with oleoyl-CoA as the acyl donor. The results obtained with arachidonoyl-CoA were similar to those with oleoyl-CoA,
with the exception of a 40% inhibition of lysophosphatidylserine:acyl-CoA acyltransferase (LPSAT) at concentrations of 50
μM or higher. At similar concentrations, merthiolate was more effective than THC in inhibiting the acyltransferases examined.
Selective effects on the acyltransferases were observed at low concentrations of merthiolate (20 μM or less). Thus, LPCAT
was most susceptible, followed by LPI acyltransferases, LPSAT, LPEAT and lysophosphatidic acid:acyl-CoA acyltransferases (LPAAT).
The presence of LPA did not affect the inhibition of LPCAT by merthiolate. Thus the resilience of LPAAT to merthiolate inhibition
was not due to chelation of the compound by the acidic lysolipid. Thiol reagents includingN-ethylmaleiamide, 5,5′-dithio-bis-nitrobenzoic acid, iodoacetate, β-mercaptoethanol and dithiothreitol had little or no effect on the acyltransferases relative
to equimolar concentrations of merthiolate. The above results indicate that merthiolate is a much more effective inhibitor
of lysophospholipid:acyl-CoA acyltransferases than is THC, and that the selectivity exhibited by merthiolate may be due to
direct and specific interaction with the acyltransferases. 相似文献