Metabolism of apical versus basolateral sn-2-monoacylglycerol and fatty acids in rodent small intestine

The metabolic fates of radiolabeled sn-2-monoacylglycerol (MG) and oleate (FA) in rat and mouse intestine, added in vivo to the apical (AP) surface in bile salt micelles, or to the basolateral (BL) surface via albumin-bound solution, were examined. Mucosal lipid products were quantified, and the results demonstrate a dramatic difference in the esterification patterns for both MG and FA, depending upon their site of entry into the enterocyte. For both lipids, the ratio of triacylglycerol to phospholipid (TG:PL) formed was approximately 10-fold higher for delivery at the AP relative to the BL surface. Further, a 3-fold higher level of FA oxidation was found for BL compared with AP substrate delivery. Incorporation of FA into individual PL species was also significantly different, with >2-fold greater incorporation into phosphatidylethanolamine (PE) and a 3-fold decrease in the phosphatidylcholine:PE ratio for AP- compared with BL-added lipid. Overnight fasting increased the TG:PL incorporation ratio for both AP and BL lipid addition, suggesting that metabolic compartmentation is a physiologically regulated phenomenon. These results support the existence of separate pools of TG and glycerolipid intermediates in the intestinal epithelial cell, and underscore the importance of substrate trafficking in the regulation of enterocyte lipid metabolism.     

Common mechanisms of monoacylglycerol and fatty acid uptake by human intestinal Caco-2 cells

Free fatty acids (FFA) andsn-2-monoacylglycerol (sn-2-MG), the twohydrolysis products of dietary triacylglycerol, are absorbed from thelumen into polarized enterocytes that line the small intestine.Intensive studies regarding FFA transport across the brush-bordermembrane of the enterocyte are available; however, little is knownabout sn-2-MG transport. We therefore studied the kineticsof sn-2-MG transport, compared with those of long-chain FFA(LCFA), by human intestinal Caco-2 cells. To mimic postprandial luminaland plasma environments, we examined the uptake of taurocholate-mixed lipids and albumin-bound lipids at the apical (AP) and basolateral (BL)surfaces of Caco-2 cells, respectively. The results demonstrate thatthe uptake of sn-2-monoolein at both the AP and BL membranes appears to be a saturable function of the monomer concentration ofsn-2-monoolein. Furthermore, trypsin preincubation inhibits sn-2-monoolein uptake at both AP and BL poles of cells.These results suggest that sn-2-monoolein uptake may be aprotein-mediated process. Competition studies also support aprotein-mediated mechanism and indicate that LCFA and LCMG may competethrough the same membrane protein(s) at the AP surface of Caco-2 cells.The plasma membrane fatty acid-binding protein (FABP_pm) isknown to be expressed in Caco-2, and here we demonstrate that fattyacid transport protein (FATP) is also expressed. These putative plasmamembrane LCFA transporters may be involved in the uptake ofsn-2-monoolein into Caco-2 cells.

     

Fatty acid uptake and metabolism in a human intestinal cell line (Caco-2): comparison of apical and basolateral incubation

Free fatty acids can enter the enterocyte via the apical or basolateral plasma membrane. We have used the Caco-2 intestinal cell line to examine the polarity of free fatty acid uptake and metabolism in the enterocyte. Differentiated Caco-2 cells form polarized monolayers with tight junctions, and express the small intestine-specific enzymes sucrase and alkaline phosphatase. Cells were grown on permeable polycarbonate Transwell filters, thus allowing separate access to the apical and basolateral compartments. Total uptake of [3H]palmitate bound to bovine serum albumin (palmitate-BSA 4:1) was twofold higher (P less than 0.05 or less) at the apical surface than at the basolateral surface. The relative apical and basolateral membrane surface areas of the Caco-2 cells, as measured by partition of the fluorophore trimethylammonium-diphenylhexatriene TMA-DPH), was found to be 1:3. Thus, apical fatty acid uptake was sixfold higher than basolateral uptake per unit surface area. Analysis of metabolites after incubation with submicellar concentrations of [3H]palmitate showed that the triacylglycerol to phospholipid (TG:PL) ratio was higher for fatty acid added to the apical as compared to the basolateral compartment (20% at 60 min, P less than 0.025). Little fatty acid oxidation was observed. Preincubation with albumin-bound palmitate, alone or with monoolein, increased the incorporation of both apical and basolateral free fatty acids into TG. The results suggest that the net uptake of long-chain free fatty acids across the apical plasma membrane is greater than uptake across the basolateral membrane. In addition, a small increase in the TG:PL ratio for apically, compared to basolaterally, added free fatty acids suggests that polarity of metabolism occurs to a limited extent in Caco-2 enterocytes.     

Vitamin A metabolism in the human intestinal Caco-2 cell line

The human intestinal Caco-2 cell line, described as enterocyte-like in a number of studies, was examined for its ability to carry out the metabolism of vitamin A normally required in the absorptive process. Caco-2 cells contained cellular retinol-binding protein II, a protein which is abundant in human villus-associated enterocytes and may play an important role in the absorption of vitamin A. Microsomal preparations from Caco-2 cells contained retinal reductase, acyl-CoA-retinol acyltransferase (ARAT), and lecithin-retinol acyltransferase (LRAT) activities, which have previously been proposed to be involved in the metabolism of dietary vitamin A in the enterocyte. When intact Caco-2 cells were provided with beta-carotene, retinyl acetate, or retinol, synthesis of retinyl palmitoleate, oleate, palmitate, and small amounts of stearate resulted. However, exogenous retinyl palmitate or stearate was not used by Caco-2 cells as a source of retinol for ester synthesis. While there was a disproportionate synthesis of monoenoic fatty acid esters of retinol in Caco-2 cells compared to the retinyl esters typically found in human chylomicrons or the esters normally synthesized in rat intestine, the pattern was consistent with the substantial amount of unsaturated fatty acids, particularly 18:1 and 16:1, found in the sn-1 position of Caco-2 microsomal phosphatidylcholine, the fatty acyl donor for LRAT. Both ARAT and LRAT have been proposed to be responsible for retinyl ester synthesis in the enterocyte.(ABSTRACT TRUNCATED AT 250 WORDS)     

Long term incubation of cardiac myocytes with oleic acid and very-low density lipoprotein reduces heparin-releasable lipoprotein lipase activity

An exogenous [³H]triolein emulsion was hydrolyzed by intact cardiac myocytes with functional LPL located on the cell surface. This surface-bound LPL could be released into the medium when cardiac myocytes were incubated with heparin. Incubation of cardiac myocytes with VLDL, or the products of TG breakdown, oleic acid or 2-monoolein, did not increase LPL activity in the medium. However, incubation of cardiac myocytes with either VLDL or oleic acid for > 60 min did reduce heparin-releasable LPL activity. In the heart, this inhibitory effect of FFA could regulate the translocation of LPL from its site of synthesis in the cardiac myocyte to its functional site at the capillary endothelium.Abbreviations LPL lipoprotein lipase - TG triacylglycerol - FFA free fatty acids - VLDL very-low density lipoprotein     

Over-Expression of Monoacylglycerol Lipase (MGL) in Small Intestine Alters Endocannabinoid Levels and Whole Body Energy Balance, Resulting in Obesity

The function of small intestinal monoacylglycerol lipase (MGL) is unknown. Its expression in this tissue is surprising because one of the primary functions of the small intestine is to convert diet-derived MGs to triacylglycerol (TG), and not to degrade them. To elucidate the function of intestinal MGL, we generated transgenic mice that over-express MGL specifically in small intestine (iMGL mice). After only 3 weeks of high fat feeding, iMGL mice showed an obese phenotype; body weight gain and body fat mass were markedly higher in iMGL mice, along with increased hepatic and plasma TG levels compared to wild type littermates. The iMGL mice were hyperphagic and displayed reduced energy expenditure despite unchanged lean body mass, suggesting that the increased adiposity was due to both increased caloric intake and systemic effects resulting in a hypometabolic rate. The presence of the transgene resulted in lower levels of most MG species in intestinal mucosa, including the endocannabinoid 2-arachidonoyl glycerol (2-AG). The results therefore suggest a role for intestinal MGL, and intestinal 2-AG and perhaps other MG species, in whole body energy balance via regulation of food intake as well as metabolic rate.     

Endothelial lipase releases saturated and unsaturated fatty acids of high density lipoprotein phosphatidylcholine

We assessed the ability of endothelial lipase (EL) to hydrolyze the sn-1 and sn-2 fatty acids (FAs) from HDL phosphatidylcholine. For this purpose, reconstituted discoidal HDLs (rHDLs) that contained free cholesterol, apolipoprotein A-I, and either 1-palmitoyl-2-oleoylphosphatidylcholine, 1-palmitoyl-2-linoleoylphosphatidylcholine, or 1-palmitoyl-2-arachidonylphosphatidylcholine were incubated with EL- and control (LacZ)-conditioned media. Gas chromatography analysis of the reaction mixtures revealed that both the sn-1 (16:0) and sn-2 (18:1, 18:2, and 20:4) FAs were liberated by EL. The higher rate of sn-1 FA cleavage compared with sn-2 FA release generated corresponding sn-2 acyl lyso-species as determined by MS analysis. EL failed to release sn-2 FA from rHDLs containing 1-O-1'-hexadecenyl-2-arachidonoylphosphatidylcholine, whose sn-1 position contained a nonhydrolyzable alkyl ether linkage. The lack of phospholipase A(2) activity of EL and its ability to liberate [(14)C]FA from [(14)C]lysophosphatidylcholine (lyso-PC) led us to conclude that EL-mediated deacylation of phosphatidylcholine (PC) is initiated at the sn-1 position, followed by the release of the remaining FA from the lyso-PC intermediate. Thin-layer chromatography analysis of cellular lipids obtained from EL-overexpressing cells revealed a pronounced accumulation of [(14)C]phospholipid and [(14)C]triglyceride upon incubation with 1-palmitoyl-2-[1-(14)C]linoleoyl-PC-labeled HDL(3), indicating the ability of EL to supply cells with unsaturated FAs.     

Monoglyceride lipase deficiency in mice impairs lipolysis and attenuates diet-induced insulin resistance

Monoglyceride lipase (MGL) influences energy metabolism by at least two mechanisms. First, it hydrolyzes monoacylglycerols (MG) into fatty acids and glycerol. These products can be used for energy production or synthetic reactions. Second, MGL degrades 2-arachidonoyl glycerol (2-AG), the most abundant endogenous ligand of cannabinoid receptors (CBR). Activation of CBR affects energy homeostasis by central orexigenic stimuli, by promoting lipid storage, and by reducing energy expenditure. To characterize the metabolic role of MGL in vivo, we generated an MGL-deficient mouse model (MGL-ko). These mice exhibit a reduction in MG hydrolase activity and a concomitant increase in MG levels in adipose tissue, brain, and liver. In adipose tissue, the lack of MGL activity is partially compensated by hormone-sensitive lipase. Nonetheless, fasted MGL-ko mice exhibit reduced plasma glycerol and triacylglycerol, as well as liver triacylglycerol levels indicative for impaired lipolysis. Despite a strong elevation of 2-AG levels, MGL-ko mice exhibit normal food intake, fat mass, and energy expenditure. Yet mice lacking MGL show a pharmacological tolerance to the CBR agonist CP 55,940 suggesting that the elevated 2-AG levels are functionally antagonized by desensitization of CBR. Interestingly, however, MGL-ko mice receiving a high fat diet exhibit significantly improved glucose tolerance and insulin sensitivity in comparison with wild-type controls despite equal weight gain. In conclusion, our observations implicate that MGL deficiency impairs lipolysis and attenuates diet-induced insulin resistance. Defective degradation of 2-AG does not provoke cannabinoid-like effects on feeding behavior, lipid storage, and energy expenditure, which may be explained by desensitization of CBR.     

Monoacylglycerol lipase activity in cardiac myocytes

Monoacylglycerol lipase activity in homogenates of isolated myocardial cells (myocytes) from rat hearts was recovered in both particulate and soluble subcellular fractions. The activity present in the microsomal (100,000 X g pellet) fraction was solubilized by treatment with Triton X-100 and combined with the 100,000 X g supernatant fraction; the properties of monoacylglycerol lipase were investigated with this soluble enzyme preparation. The Km for the hydrolysis of a 2-monoolein substrate was 16 microM. The rates of hydrolysis of 1-monoolein and 2-monoolein were identical, and 1-monoolein was a competitive inhibitor (Ki = 20 microM) of the hydrolysis of 2-monoolein. Monoacylglycerol lipase activity was regulated by product inhibition according to the following order of potency: fatty acyl CoA greater than free fatty acids greater than fatty acyl carnitine.     

Global deletion of MGL in mice delays lipid absorption and alters energy homeostasis and diet-induced obesity

Monoacylglycerol lipase (MGL) is a ubiquitously expressed enzyme that catalyzes the hydrolysis of monoacylglycerols (MGs) to yield FFAs and glycerol. MGL contributes to energy homeostasis through the mobilization of fat stores and also via the degradation of the endocannabinoid 2-arachidonoyl glycerol. To further examine the role of MG metabolism in energy homeostasis, MGL^−/− mice were fed either a 10% (kilocalories) low-fat diet (LFD) or a 45% (kilocalories) high-fat diet (HFD) for 12 weeks. Profound increases of MG species in the MGL^−/− mice compared with WT control mice were found. Weight gain over the 12 weeks was blunted in both diet groups. MGL^−/− mice were leaner than WT mice at both baseline and after 12 weeks of LFD feeding. Circulating lipids were decreased in HFD-fed MGL^−/− mice, as were the levels of several plasma peptides involved in glucose homeostasis and energy balance. Interestingly, MGL^−/− mice had markedly reduced intestinal TG secretion following an oral fat challenge, suggesting delayed lipid absorption. Overall, the results indicate that global MGL deletion leads to systemic changes that produce a leaner phenotype and an improved serum metabolic profile.     

Distribution of phosphatidylcholine molecular species between mixed micelles and phospholipid-cholesterol vesicles in human gallbladder bile: dependence on acyl chain length and unsaturation.

The partitioning of phosphatidylcholine (PC) molecular species between mixed micelles and vesicles was studied in each of seven human gallbladder biles. Biles were fractionated by Sephacryl S-300 SF gel filtration chromatography, and PC species in the micellar and vesicular fractions were quantitated by high performance liquid chromatography. Micelles were enriched in species containing unsaturated acyl groups (e.g., 16:1-18:2, 18:1-18:2, and 18:1-18:3); vesicles were enriched in more highly saturated species (e.g., 16:0-16:1, 16:0-18:1, and 18:0-18:1). Separate multivariate analyses for each bile demonstrated that the distribution of PC species between vesicles and micelles was related to the degree of sn-1 and sn-2 unsaturation, and sn-1, but not sn-2, chain length. In addition, the tendency to partition into the micellar phase was particularly marked when unsaturation was present at both the sn-1 and sn-2 positions. When this interaction was included in the multivariate analyses, the regression models accounted for virtually all of the variation in PC partitioning (for each of the seven patients r2 = 0.92-0.98, P less than 0.03). These results suggest that the partitioning of PC species between micelles and vesicles is strictly determined by sn-1 chain length and the degree of unsaturation at both the sn-1 and sn-2 positions. In light of recent reports that fatty acyl composition influences the cholesterol content of vesicles and micelles in model biles, these results raise the possibility that diet-induced alterations in the phospholipid species and the relative proportions of biliary lipid particles may influence the cholesterol-carrying capacity of bile.     

Inhibitory effect of lysophosphatidylcholine on pancreatic lipase-mediated hydrolysis in lipid emulsion

In the lipid metabolism pathway, dietary lipid emulsified with bile salts and phospholipids is mainly digested by pancreatic lipase into free fatty acids and monoacylglycerols. In order to study substrate recognition mechanism of a pancreatic lipase, we investigated its catalytic property toward the lipid emulsion prepared with long- or intermediate-chain acylglycerols and several physiological surfactants. When lysophosphatidylcholine (LysoPC), rather than bile salts or phospholipid, was incorporated into the lipid emulsion, it caused an increase in the Km(app) and a decrease in the Vmax(app) values in the interactions between the lipase and triacylglycerol (triolein or tricaprin). This indicated that LysoPC inhibited hydrolysis by decreasing both the substrate affinities and the catalytic activity of this lipase. Interestingly, further addition of taurodeoxycholic acid sodium salts or phospholipid completely restored the inhibitory effect of LysoPC on hydrolysis by lipase. On the other hand, the change in these kinetic values between the lipase and two 1-monoacylglycerols (1-monocaprin and 1-monoolein) were not particularly large when LysoPC was added. Particle size analysis of the lipid emulsion composed of LysoPC and triacylglycerols showed that most of the particles were less than 200 nm in size, which was smaller than the particle size in the triacylglycerol emulsions containing bile salts or phospholipid. The composition of the emulsion would affect its surface characteristics and thus contribute to changing lipase activity.     

Corticosteroid effect on Caco-2 cell lipids depends on cell differentiation

Previous studies from our laboratory have indicated that secondary hyperaldosteronism affects phospholipids of rat colonic enterocytes. To assess whether this represents a direct effect of mineralocorticoids on enterocytes, the role of aldosterone and dexamethasone in the regulation of lipid metabolism was examined in Caco-2 cells during development of their enterocyte phenotype. Differentiation of Caco-2 cells was associated with increased levels of triglycerides (TG) and cholesteryl esters (CE), a decreased content of cholesterol and phospholipids and changes in individual phospholipid classes. The phospholipids of differentiated cells had a higher content of n-6 polyunsaturated fatty acids (PUFA) and lower amounts of monounsaturated (MUFA) and saturated fatty acids than subconfluent undifferentiated cells. Differentiated cells exhibited a higher ability to incorporate [3H]arachidonic acid (AA) into cellular phospholipids and a lower ability for incorporation into TG and CE. Incubation of subconfluent undifferentiated cells with aldosterone or dexamethasone was without effect on the content of lipids, their fatty acids and [3H]AA incorporation. In contrast, aldosterone treatment of differentiated cells diminished the content of TG, increased the content of phospholipids and modulated their fatty acid composition. The percentage of n-6 and n-3 PUFA in phospholipids was increased and that of MUFA decreased, whereas no changes in TG were observed. The incorporation of [3H]AA into phospholipids was increased and into TG decreased and these changes were blocked by spironolactone. Treatment of differentiated cells with dexamethasone increased their CE content but no effect was identified upon other lipids, their fatty acid composition and on the incorporation of [3H]AA. As expected for the involvement of corticosteroid hormones the mineralocorticoid and glucocorticoid receptors were identified in Caco-2 cells by RT-PCR. The results suggest that aldosterone had a profound influence on lipid metabolism in enterocytes and that its effect depends on the stage of differentiation. The aldosterone-dependent changes occurring in phospholipids and their fatty acid composition may reflect a physiologically important phenomenon with long-term consequences for membrane structure and function.     

Synthesis of sn-1,2-diacylglycerols by monoacylglycerol acyltransferase from Manduca sexta fat body

The pathway for the synthesis of sn-1,2-diacylglycerol stimulated by the action of adipokinetic hormone (AKH) in the insect fat body is unknown. Previous results from this laboratory suggested that the hydrolysis of stored triacylglycerol to sn-2-monoacylglycerol followed by the stereospecific acylation of sn-2-monoacylglycerol catalyzed by a monoacylglycerol-acyltransferase (MGAT) could be the major route of AKH-stimulated sn-1,2-diacylglycerol synthesis. Thus, MGAT might represent a key enzyme of this pathway. In this study we characterized the MGAT activity from the Manduca sexta fat body. The activity, which was assayed by acylation of 2-monoolein using radioactive labeled palmitoyl-CoA, was found to be primarily a microsomal enzyme. The products of the acylation of 2-monoolein were 1,2-diacylglycerol (40–50%), 1,3-diacylglycerol (20–30%), and triacylglycerol (30–40%). The presence of triacylglycerol as a product revealed the presence of diacylglycerol-acyltransferase activity in the fat body microsomes. The pH optimum of MGAT activity was 7.0, and the dependence of the activity on the concentration of 2-monoolein showed saturation kinetics. An endogenous MGAT activity, which represented 20% of the maximal activity observed with added substrate, was detected. Optimal concentrations of palmitoyl-CoA ranged between 0.10–0.20 mM. The specific activity of MGAT, measured under optimal conditions, was about 0.6 nmol DG formed/min-mg protein. MGAT activity was greatest with 2-monoolein, and lower activity was observed when a saturated 2-monoacylglycerol was employed. The activity observed with sn-1-monoacylglycerol was lower than that observed with sn-2-monoacylglycerol. AKH did not stimulate MGAT activity, suggesting that either the enzyme is not under hormonal regulation or the monoacylglycerol pathway is not involved in the AKH-stimulated production of sn-1,2-diacylglycerol in the M. sexta fat body. © 1996 Wiley-Liss, Inc.     

Modulatory effect of temperature on the influence of dietary linolenic (18 : 3 n-3) and linoleic (18 : 2 n-6) acids on the gonadal recrudescence in Clarias batrachus (L.)

During the late postspawning phase, freshwater catfish Clarias batrachus fed a diet rich in linseed oil (18: 3 n-3) (LSO) and 13L : 11D photoperiod and at 28° C showed increases in ovarian weight and plasma levels of testosterone and oestradiol-17β, and in concentrations of free fatty acids (FFA), monoglycerides (MG), diglycerides (DG), triglycerides (TG), phospholipids (PL) and esterified cholesterol (CE) in the liver, plasma and ovary. In fish fed a diet rich in sunflower oil (18: 2 n-6) (SFO) under the same conditions, plasma testosterone decreased sharply, concentrations of FFA, DG and TG increased in the liver and plasma and ovarian levels of TG and CE decreased. Neither diet was gonadostimulatory when fed at 18°C.     

Cardiac triacylglycerol content and lipase activity during recovery from exercise

Female rats swam for 2-h to determine the temporal relationship between triglyceride (TG) repletion and TG lipase activity in the heart during recovery from exercise. Immediately after the exercise, plasma free fatty acids (FFA) had increased from a resting value of 0.44 +/- 0.04 to 0.84 +/- 0.04 mM. Heart TG concentration was reduced 75%, whereas the glycogen level was decreased 34% below control. TG lipase activity was elevated 33% above control activity. One hour after the end of the exercise, lipolytic activity was still 26% above control and did not return to the resting level until the 4th h of recovery. The cardiac TG concentration was back to control levels by the 2nd h after the swim. Plasma FFA concentrations remained elevated during the first 4 h of recovery and were back to the control level by h 8. Cardiac glycogen was "supercompensated" during recovery h 1 and 2 and returned to the preexercise level by h 4. These data indicate that TG is being synthesized in the heart while lipolytic enzyme activity is elevated above control levels. This points out that the rate of TG synthesis is in excess of the hydrolysis. Since plasma FFA concentrations are elevated during periods of augmented TG synthesis, substrate availability, namely plasma FFA, may play a key role in regulating the size of the intracellular TG pool.     

Crystal structure of the Saccharomyces cerevisiae monoglyceride lipase Yju3p

Monoglyceride lipases (MGLs) are a group of α/β-hydrolases that catalyze the hydrolysis of monoglycerides (MGs) into free fatty acids and glycerol. This reaction serves different physiological functions, namely in the last step of phospholipid and triglyceride degradation, in mammalian endocannabinoid and arachidonic acid metabolism, and in detoxification processes in microbes. Previous crystal structures of MGLs from humans and bacteria revealed conformational plasticity in the cap region of this protein and gave insight into substrate binding. In this study, we present the structure of a MGL from Saccharomyces cerevisiae called Yju3p in its free form and in complex with a covalently bound substrate analog mimicking the tetrahedral intermediate of MG hydrolysis. These structures reveal a high conservation of the overall shape of the MGL cap region and also provide evidence for conformational changes in the cap of Yju3p. The complex structure reveals that, despite the high structural similarity, Yju3p seems to have an additional opening to the substrate binding pocket at a different position compared to human and bacterial MGL. Substrate specificities towards MGs with saturated and unsaturated alkyl chains of different lengths were tested and revealed highest activity towards MG containing a C18:1 fatty acid.     

Molecular interpretation of fluorescence solvent relaxation of Patman and 2H NMR experiments in phosphatidylcholine bilayers

The analysis of time-dependent fluorescence shifts of the bilayer probe 6-hexadecanoyl-2-(((2-(trimethylammonium)ethyl)methyl)amino)naphthalene chloride (Patman) offers valuable information on the hydration and dynamics of phospholipid headgroups. Quenching studies on vesicles composed of four phosphatidylcholines with different hydrocarbon chains (18:1c9/18:1c9, DOPC; 16:0/18:1c9, POPC; 18:1c9/16:0, OPPC; 18:1c6/18:1c6, PCDelta6) show that the chromophore of Patman is defined located at the level of the sn-1 ester-group in the phospholipid, which is invariant to the hydrocarbon chain. The so-called solvent relaxation (SR) approach as well as solid-state 2H NMR reveals that DOPC and PCDelta6 are more hydrated than POPC and OPPC. A strong dependence of SR kinetics on the position of double bond in the investigated fatty acid chains was observed. Apparently, the closer the double bond is located to the hydrated sn-1 ester-group, the more mobile this group becomes. This work demonstrates that the SR approach can report mobility changes within phospholipid bilayers with a remarkable molecular resolution.     

Diacylglycerol metabolism and arachidonic acid release in human fetal membranes and decidua vera

Diacylglycerol lipase activity has been demonstrated in human fetal membranes and decidua vera tissues. The specific activity of the enzyme is highest in the microsomal fraction of decidua vera tissue. The acylester bond at the sn-1 position of 1,2-diacyl-sn-glycerol is hydrolyzed followed by release of the fatty acid at the sn-2 position. The diacylglycerol lipase activity present in the microsomal fraction of decidua vera tissue hydrolyzes preferentially a diacylglycerol containing an arachidonoyl group in the sn-2 position. Monoacylglycerol lipase activity was also demonstrated in these tissues. The specific activity of monoacylglycerol lipase was significantly greater than that of diacylglycerol lipase and catalyzed preferentially the hydrolysis of monoacylglycerols containing an arachidonyl group in the sn-2 position. Based on the subcellular distribution and the differential effects of various inhibitors, we suggest that the monoacylglycerol lipase and diacylglycerol lipase in decidua vera tissue are 2 distinct enzymes. Diacylglycerol kinase specific activity was examined also and was found to be 4-5 times greater in amnion than in either chorion laeve or decidua vera. The importance of diacylglycerol metabolism in the mechanism of arachidonic acid release and prostaglandin biosynthesis is discussed.