digalactosyldiacylglycerol and sulfoquinovosyl-diglyceride

Photosystem II (PSII), the first supercomplex of the electron transport chain, governs the energy transfer using harvested light energy, which is transformed into biochemical energy. Phosphatidylglycerol and sulfoquinovosyl diacylglycerol, the anionic lipids of photosynthetic organisms, together with a neutral lipid, digalactosyldiacylglycerol, assist in the assembly of photosynthetic complexes. These lipids and carotenoids serve as mortar for the proteins which act as bricks in the construction of the active photosynthetic machinery, and they have determinative roles in the oligomerization of protein subunits. X-ray crystallographic localization of glycerolipids and carotenoids revealed that they are present at functionally and structurally important sites of both the PSI and PSII reaction centers. Phosphatidylglycerol is involved in the formation of the reaction-center oligomers and controls electron transport at the acceptor site of PSII. Digalactosyldiacylglycerol, together with phosphatidylglycerol, is involved in the electron transport at the donor site. Phosphatidylglycerol and carotenoids are needed to glue CP43 to the reaction center core. Carotenoids are protective agents, which prevent photosynthetic complexes from degradation caused by reactive oxygen species.

Topics: Arabidopsis; beta Carotene; Carotenoids; Chlamydomonas; Galactolipids; Glycolipids; Phosphatidylglycerols; Photosynthesis; Photosynthetic Reaction Center Complex Proteins; Photosystem II Protein Complex; Synechococcus; Thylakoids

Plant chloroplasts have complex membrane systems. Among these, thylakoids serve as the sites for photosynthesis and photosynthesis-related adaptation. In addition to the photosynthetic membrane complexes and associated molecules, lipids in the thylakoid membranes, are predominantly composed of MGDG (monogalactosyldiacylglycerol), DGDG (digalactosyldiacylglycerol), SQDG (sulfoquinovosyldiacylglycerol) and PG (phosphatidylglycerol), play essential roles in shaping the thylakoid architecture, electron transfer, and photoregulation. In this review, we discuss the effect of abiotic stress on chloroplast structure, the changes in membrane lipid composition, and the degree of unsaturation of fatty acids. Advanced understanding of the mechanisms regulating chloroplast membrane lipids and unsaturated fatty acids in response to abiotic stresses is indispensable for improving plant resistance and may inform the strategies of crop breeding.

Topics: Chloroplasts; Fatty Acids; Galactolipids; Glycolipids; Lipid Metabolism; Membrane Lipids; Phosphatidylglycerols; Stress, Physiological

Fatty acid desaturases (FADs) represent a class of oxygen-dependent enzymes that dehydrogenate C-C bonds in the fatty acids (FAs) producing unsaturated CC double bonds that markedly change the properties of biological membranes. FADs are highly specific towards their acyl substrates, the position and configuration of the introduced double bonds. The double bond positioning of soluble acyl-carrier-protein Δ9-FADs was determined relative to the carboxyl end of a FA. Similar mode was suggested for the acyl-lipid Δ12-FADs (also known as ω6-FADs), however, their exact counting order remain unknown. Here we used monounsaturated odd- (17:1Δ

Topics: Carbon; Cyanobacteria; Fatty Acid Desaturases; Fatty Acids, Monounsaturated; Galactolipids; Glycolipids; Lipid Metabolism; Phosphatidylglycerols; Spectrometry, Mass, Electrospray Ionization; Synechococcus; Synechocystis

The membranes of Zea mays (maize) mesophyll cell (MC) chloroplasts are more vulnerable to salinity stress than are those of bundle sheath cell (BSC) chloroplasts. To clarify the mechanism underlying this difference in salt sensitivity, we monitored changes in the glycerolipid and fatty acid compositions of both types of chloroplast upon exposure to salinity stress. The monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) contents were higher in MC chloroplasts than in BSC chloroplasts, in both the presence and absence of salt treatment. Under salt conditions, the MGDG level in MC chloroplasts was significantly lower than under normal conditions, while it was unchanged in BSC chloroplasts. In both types of chloroplast, the contents of DGDG, phosphatidylglycerol and phosphatidylinositol remained at the same levels in control and salt-treated plants, whereas sulfoquinovosyldiacylglycerol and phosphatidylcholine were significantly lower and higher, respectively, upon salt treatment. In addition, the fatty acid composition and double bond index of individual lipid classes were changed by salt treatment in both BSC and MC chloroplasts, although these factors had no effect on glycerolipid content. These findings suggest that the difference in salt sensitivity of MC and BSC chloroplast membranes is related to differences in MGDG responses to salinity. Thus, we propose that the low MGDG content and the low sensitivity of MGDG to salinity in BSC chloroplasts render them more tolerant than MC chloroplasts to salinity stress.

Topics: Chloroplasts; Galactolipids; Glycolipids; Lipid Metabolism; Membranes; Mesophyll Cells; Salinity; Sodium Chloride; Stress, Physiological; Zea mays

We demonstrate improved power of Iatroscan thin layer chromatography/flame ionization detection (TLC-FID) technique for analysis of complex marine lipid mixture by developing protocol for the separation and analysis of glycolipids including sulfoquinovosyldiacylglycerols (SQDG), monogalactosyldiacylglycerols (MGDG) and digalactosyldiacylglycerols (DGDG). We have modified the common protocol used so far for the analysis of lipid classes by replacing the elution step which uses pure acetone for the elution of acetone mobile polar lipids, with the elution step containing chloroform-acetone (72:28, v:v) for separation of MGDG and DGDG. To separate SQDG from the complex lipid matrix we introduced solvent mixture acetone-chloroform-methanol-formic acid (33:33:33:0.6, v:v:v:v). Quantification of glycolipid classes was performed after calibration with glycolipid standards for the masses between 0.2 and 2.7-5.0μg. With this new protocol we have successfully separated three glycolipids from the complex particulate lipid mixture of the seawater samples. Such an approach extends the power of existing protocol for the analysis of lipids which altogether ensure detection and quantification of 18 lipid classes what was demonstrated on seawater samples. This enables to gain a very broad system overview of the particularly complex environments as are seas, oceans and freshwaters.

Topics: Chromatography, Thin Layer; Flame Ionization; Galactolipids; Glycolipids; Seawater; Water Pollutants, Chemical

MGDG leads to a dimerization of isolated, monomeric PSII core complexes. SQDG and PG induce a detachment of CP43 from the PSII core, thereby disturbing the intrinsic PSII electron transport. The influence of the four thylakoid membrane lipids monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), sulfoquinovosyldiacylglycerol (SQDG) and phosphatidylglycerol (PG) on the structure and function of isolated monomeric photosystem (PS) II core complexes was investigated. Incubation with the negatively charged lipids SQDG and PG led to a loss of the long-wavelength 77 K fluorescence emission at 693 nm that is associated with the inner antenna proteins. The neutral galactolipids DGDG and MGDG had no or only minor effects on the fluorescence emission spectra of the PSII core complexes, respectively. Pigment analysis, absorption and 77 K fluorescence excitation spectroscopy showed that incubation with SQDG and PG led to an exposure of chlorophyll molecules to the surrounding medium followed by conversion to pheophytin under acidic conditions. Size-exclusion chromatography and polypeptide analysis corroborated the findings of the spectroscopic measurements and pigment analysis. They showed that the negatively charged lipid SQDG led to a dissociation of the inner antenna protein CP43 and the 27- and 25-kDa apoproteins of the light-harvesting complex II, that were also associated with a part of the PSII core complexes used in the present study. Incubation of PSII core complexes with MGDG, on the other hand, induced an almost complete dimerization of the monomeric PSII. Measurements of the fast PSII fluorescence induction demonstrated that MGDG and DGDG only had a minor influence on the reduction kinetics of plastoquinone QA and the artificial PSII electron acceptor 2,5-dimethyl-p-benzoquinone (DMBQ). SQDG and, to a lesser extent, PG perturbed the intrinsic PSII electron transport significantly.

Topics: Benzoquinones; Cyclohexenes; Electron Transport; Galactolipids; Glycolipids; Membrane Lipids; Photosystem II Protein Complex; Plastoquinone; Spectrometry, Fluorescence; Spinacia oleracea; Thylakoids

The present study shows that thylakoid membranes of the diatom Cyclotella meneghiniana contain much higher amounts of negatively charged lipids than higher plant or green algal thylakoids. Based on these findings, we examined the influence of SQDG on the de-epoxidation reaction of the diadinoxanthin cycle and compared it with results from the second negatively charged thylakoid lipid PG. SQDG and PG exhibited a lower capacity for the solubilization of the hydrophobic xanthophyll cycle pigment diadinoxanthin than the main membrane lipid MGDG. Although complete pigment solubilization took place at higher concentrations of the negatively charged lipids, SQDG and PG strongly suppressed the de-epoxidation of diadinoxanthin in artificial membrane systems. In in vitro assays employing the isolated diadinoxanthin cycle enzyme diadinoxanthin de-epoxidase, no or only a very weak de-epoxidation reaction was observed in the presence of SQDG or PG, respectively. In binary mixtures of the inverted hexagonal phase forming lipid MGDG with the negatively charged bilayer lipids, comparable suppression took place. This is in contrast to binary mixtures of MGDG with the neutral bilayer lipids DGDG and PC, where rapid and efficient de-epoxidation was observed. In complex lipid mixtures resembling the lipid composition of the native diatom thylakoid membrane, we again found strong suppression of diadinoxanthin de-epoxidation due to the presence of SQDG or PG. We conclude that, in the native thylakoids of diatoms, a strict separation of the MGDG and SQDG domains must occur; otherwise, the rapid diadinoxanthin de-epoxidation observed in intact cells upon illumination would not be possible.

Topics: Algal Proteins; Chromatography, High Pressure Liquid; Diatoms; Galactolipids; Glycolipids; Lipid Metabolism; Membranes, Artificial; Phosphatidylglycerols; Solubility; Thylakoids; Xanthophylls

A human replication initiation protein, Cdt1, is a central player in the cell cycle regulation of DNA replication, and geminin down-regulates Cdt1 function by direct binding. It has been demonstrated that Cdt1 hyperfunction resulting from Cdt1-geminin imbalance, for example, by geminin silencing with small interfering RNA, induces DNA re-replication and eventual cell death in some cancer-derived cell lines. We established a high throughput screening system based on a modified enzyme linked immunosorbent assay to identify compounds that interfere with human Cdt1-geminin binding. Using this system, we screened inhibitors from natural materials containing food components, and found that a glycolipid, sulfoquinovosyl diacylglycerol (SQDG), from spinach can inhibit Cdt1-geminin interaction in vitro, with 50% inhibition observed at concentrations of 1.79mug/ml. Other major glycolipids, such as monogalactosyl diacylglycerol (MGDG) and digalactosyl diacylglycerol (DGDG) from spinach, had no influence. Surface plasmon resonance analysis demonstrated that SQDG bound selectively to Cdt1, but did not interact with geminin. Using three-dimensional computer modeling analysis, SQDG was considered to interact with the geminin interaction interface on Cdt1, and the sulfate group of SQDG was assumed to make hydrogen bonds with the residue of Arg346 of Cdt1. These data could help to further understanding of the structure and function of Cdt1. In addition, SQDG could be a clue to developing more appropriate inhibitors of Cdt1-geminin interactions.

Topics: Animals; Binding Sites; Cell Cycle Proteins; Computer Simulation; DNA-Binding Proteins; Galactolipids; Geminin; Glycolipids; Humans; Mice; Nuclear Proteins; Spinacia oleracea

We succeeded in purifying the fraction of monogalactosyl diacylglycerol (MGDG), digalactosyl diacylglycerol (DGDG), and sulfoquinovosyl diacylglycerol (SQDG) containing the major glycolipids from a green vegetable, spinach (Spinacia oleraceaL.). This glycolipids fraction inhibited the activities of replicative DNA polymerases (pols) such as alpha, delta, and epsilon, and mitochondrial pol gamma with IC50 values of 44.0-46.2 microg/ml, but had no influence on the activity of repair-related pol beta. The fraction also inhibited the proliferation of human cervix carcinoma (HeLa) cells with LD50 values of 57.2 microg/ml. In an in vivo anti-tumor assay on nude mice bearing solid tumors of HeLa cells, the fraction was shown to be a promising suppressor of solid tumors. Histopathological examination revealed that tumor necrosis with hemorrhage was significantly enhanced with the glycolipids fraction in vivo. The spinach glycolipids fraction might be a potent anti-tumor compound, and this fraction may be a healthy food substance with anti-tumor activity.

Topics: Animals; Antineoplastic Agents, Phytogenic; Cell Division; DNA-Directed DNA Polymerase; Dose-Response Relationship, Drug; Food, Organic; Galactolipids; Glycolipids; HeLa Cells; Humans; Inhibitory Concentration 50; Lethal Dose 50; Mice; Mice, Nude; Nucleic Acid Synthesis Inhibitors; Spinacia oleracea

Anti-cancer activity of some glycolipids from animals and plants has been demonstrated, although it was unknown whether the glycolipids had anti-angiogenic activity. The effects of the purified three glycolipids, monogalactosyl diacylglycerol (MGDG), digalactosyl diacylglycerol (DGDG), and sulfoquinovosyl diacylglycerol (SQDG) from the green vegetable spinach (Spinacia oleracea L.) were examined on in vitro and ex vivo angiogenesis models. MGDG and SQDG suppressed microvessel growth in an ex vivo angiogenesis model using a rat aortic ring. The glycolipids inhibited human umbilical vein endothelial cell (HVUEC) tube formation on a reconstituted basement membrane and HUVEC proliferation. These results demonstrate that glycolipids from spinach would suppress tumor growth by suppressing angiogenesis and might be candidates for anti-cancer or anti-angiogenic materials.

Topics: Angiogenesis Inhibitors; Animals; Aorta, Thoracic; Blood Vessels; Cell Line; Cell Proliferation; Dose-Response Relationship, Drug; Endothelial Cells; Galactolipids; Glycolipids; Humans; In Vitro Techniques; Male; Plant Extracts; Rats; Spinacia oleracea; Umbilical Veins

In plant cells, the synthesis of monogalactosyldiacylglycerol (MGDG) is catalyzed within plastid envelope membranes by MGD proteins. MGDG synthesis was also reported in apicomplexan parasites, a phylum of protists harbouring a plastid that proved essential for the parasite survival. MGD activity is therefore a potent target for herbicidal and anti-parasitic molecules. In this study, we describe a detailed in vitro refolding protocol for denatured recombinant MGD accumulated in inclusion bodies from transformed Escherichia coli. The refolding process was dependent on CHAPS detergent and lipids, such as diacylglycerol and phosphatidylglycerol, as well as bivalent metals. Owing to this refolding procedure, the recombinant MGD protein from spinach was purified to homogeneity, allowing a definite characterization of its non-processivity and an investigation of its dimerization using cross-linking reagents. Additionally, using the portion of recombinant enzyme that accumulates in an active form in bacterial membranes, we developed a miniature assay for high-throughput screening for inhibitors.

Topics: Chromatography, Gel; Chromatography, Ion Exchange; Chromatography, Thin Layer; Cross-Linking Reagents; Diglycerides; Dimerization; Electrophoresis, Polyacrylamide Gel; Escherichia coli; Ethylmaleimide; Galactolipids; Galactosyltransferases; Gene Deletion; Gene Expression; Genetic Vectors; Glycolipids; Hydroxyapatites; Inclusion Bodies; Kinetics; Liposomes; Maleimides; Plant Proteins; Plants; Protein Denaturation; Protein Folding; Recombinant Proteins; Spinacia oleracea; Temperature; Urea; Uridine Diphosphate Galactose

The effects of the bleaching herbicides amitrole (125 micro M) and norflurazon (100 micro M) on etioplast lipids were studied in barley plants (Hordeum vulgare L. cv. Express) grown for 7 d either at 20 degrees C or 30 degrees C in darkness. Total lipid, glycolipid and phospholipid contents of control etioplasts were increased at 30 degrees C in comparison with those at 20 degrees C. The two herbicides caused a decrease in the total lipid, glycolipid and phospholipid amounts compared to the untreated etioplasts and lowered the lipid to protein ratio. In the controls, monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) accounted for about 66 mol% of the etioplast polar lipids, while the remainder was represented by sulphoquinovosyldiacylglycerol (SQDG) and phosphatidylglycerol (PG), in approximately equal proportions. Both amitrole and norflurazon increased MGDG at both temperatures, but decreased DGDG except with norflurazon at 30 degrees C. As a consequence, the MGDG to DGDG molar ratio was higher in the herbicide-treated etioplasts compared to the controls at both the growth temperatures. The amount of the negatively charged polar lipids SQDG and PG were decreased by treatments with amitrole at 20 degrees C and norflurazon at 30 degrees C. The two herbicides determined different responses in the fatty acid unsaturation of the individual polar lipids. Changes in the lipid composition of etioplasts and the interaction between the pigment-protein complex, protochlorophyllide-NADPH-protochlorophyllide oxidoreductase, and polar lipids are discussed.

Topics: Amitrole; Chlorophyll; Darkness; Diglycerides; Galactolipids; Glycolipids; Herbicides; Hordeum; Light; Lipid Metabolism; Oxidoreductases; Oxidoreductases Acting on CH-CH Group Donors; Phospholipids; Plant Leaves; Plant Proteins; Plastids; Pyridazines; Temperature

This study reports a simple and sensitive method for determining the absolute configuration of the glycerol moieties in glycoglycerolipids. The method is based on chiral phase high-performance liquid chromatography (HPLC) separations of enantiomeric di- and monoacylglycerols released from glycosyldi- and monoacylglycerols, respectively, by periodate oxidation followed by hydrazinolysis. The released di- and monoacylglycerols were chromatographed as their 3,5-dinitrophenylurethane (3,5-DNPU) and bis(3,5-DNPU) derivatives, respectively. The derivatives were separated on two chiral phases of opposite configuration, (R)- and (S)-1-(1-naphthyl)ethylamine polymers for diacylglycerols and N-(R)- -(1-naphthyl)ethylaminocarbonyl-(S)-valine and N-(S)-1 -(1-naphthyl)ethylamino-carbonyl-(R)-valine for monoacylglycerols. Clear enantiomer separations, which permit the assignment of the glycerol configuration, were achieved for sn-1,2(2,3)-diacyl- and sn-1(3)-monoacylglycerols generated from linseed oil triacylglycerols by partial Grignard degradation on all the chiral stationary phases employed. Using the method, we have determined the glycerol configuration in the glycosyldiacylglycerols (monogalactosyl-, digalactosyl-, and sulfquinovosyldiacylglycerols) and glycosylmonoacylglycerols (monogalactosyl-, digalactosyl-, and sulfoquinovosylmonoacylglycerols) isolated from spinach leaves and the coralline red alga Corallina pilulifera. The results clearly showed that the glycerol moieties in all the glycoglycerolipids examined have S-configuration (sn-1,2-diacyl- and sn-1-monoacylglycerols). The new method demonstrates that chiral phase HPLC provides unambiguous information on the configuration of the glycerol backbone in natural glycosyldi- and monoacylglycerols, and that the two-step liberation of the free acylglycerols does not compromise glycerol chirality.

Topics: Chromatography, High Pressure Liquid; Diglycerides; Galactolipids; Glycerides; Glycerol; Glycolipids; Molecular Conformation; Rhodophyta; Spinacia oleracea; Stereoisomerism

Monolayers of seven fractions of natural lipids (phosphatidyl inositol, sulfoquinovosyl diacylglycerol, phosphatidylcholine, digalactosyl diacylglycerol, phosphatidyl glycerol, phosphatidylethanolamine, monogalactosyl diacylglycerol), isolated from the photoautotrophic cell culture of the moss Marchantia polymorpha grown under normal and light-stress conditions, have been prepared for the first time. We have shown that the high-intensity light affects the area occupied by the lipid molecule. In the case of digalactosyl diacylglycerol and phosphatidyl glycerol fractions, after the light stress the area significantly increased from 0.50 to 0.80 nm2 and from 0.47 to 0.63 nm2, respectively, and in the case of the sulfoquinovosyl diacylglycerol fraction, the area decreased from 0.40 to 0.32 nm2. These results are in agreement with our previous data on the redistribution of the double bonds in the aliphatic chains of these lipids and can be used to characterize the state of the lipid bilayer of the thylakoid membranes.

Topics: Bryopsida; Cells, Cultured; Chromatography, Thin Layer; Diglycerides; Galactolipids; Glycolipids; Light; Membrane Lipids; Phosphatidylcholines; Phosphatidylethanolamines; Phosphatidylglycerols; Phosphatidylinositols; Plants; Thylakoids

In this study we present evidence that one of two reactions of the xanthophyll cycle, violaxanthin de-epoxidation, may occur in unilamellar egg phosphatidylcholine vesicles supplemented with monogalactosyldiacylglycerol (MGDG). Activity of violaxanthin de-epoxidase (VDE) in this system was found to be strongly dependent on the content of MGDG in the membrane; however, only to a level of 30 mol%. Above this concentration the rate of violaxanthin de-epoxidation decreased. The effect of individual thylakoid lipids on VDE-independent violaxanthin transformation was also investigated and unspecific effects of phosphatidylglycerol and sulphoquinovosyldiacyglycerol, probably related to the acidic character of these lipids, were found. The presented results suggest that violaxanthin de-epoxidation most probably takes place inside MGDG-rich domains of the thylakoid membrane. The described activity of the violaxanthin de-epoxidation reaction in liposomes opens new possibilities in the investigation of the xanthophyll cycle and may contribute to a better understanding of this process.

Topics: beta Carotene; Diglycerides; Enzyme Inhibitors; Galactolipids; Glycolipids; Kinetics; Liposomes; Lutein; Medicago sativa; Oxidoreductases; Phosphatidylcholines; Plant Leaves; Thylakoids; Triticum; Xanthophylls

Microcalorimetry was used to show that transition-temperature ranges of phospho- and glycolipids of the brown marine alga Laminaria japonica were similar (from -62 to -47 degrees C up to 62-65 degrees C), except for monogalactosyldiacylglycerol, the low-temperature limit of which was shifted to -78 degrees C. As was shown by polarizing microscopy, the low-enthalpy peaks at temperatures of approx. 30-45 degrees C corresponded to isotropic melting of galactolipids and coincided with the high-temperature limit for photosynthetic and mitochondrial activity of the algae. As a whole, a classical interrelation was observed between thermotropic behaviour and the fatty acid unsaturation of lipids.

Topics: Acclimatization; Calorimetry, Differential Scanning; Diglycerides; Fatty Acids; Fatty Acids, Unsaturated; Galactolipids; Glycolipids; Membrane Lipids; Phaeophyceae; Phospholipids; Seawater; Temperature

Digalactosyldiacylglycerol (DGDG) suppressed the inhibition by sulfoquinovosyldiacylglycerol (SQDG) of an alpha-glucosidase reaction. Suppressing was considered to be an apparent decrease in inhibitory activity of SQDG ascribed to direct interaction between SQDG and DGDG. This suppression was presumed to be caused by less access of SQDG to the enzyme because SQDG and DGDG formed mixed micelles.

Topics: Drug Interactions; Galactolipids; Glucosidases; Glycolipids; Mathematics; Micelles; Phaeophyceae; Rhodophyta

Monogalactosyldiacylglycerols (MGDG), digalactosyldiacylglycerols (DGDG) and sulfoquinovosyldiacylglycerols (SQDG) are major lipids in vegetable food. Their digestion and absorption are unknown. This study examines the hydrolysis of galactolipids in vitro with human duodenal contents, pancreatic juice, and purified human pancreatic lipases. Galactolipids were incubated with human duodenal contents, pancreatic juice, pure pancreatic carboxyl ester lipase (CEL), and colipase-dependent lipase with colipase (Lip-Col). Hydrolysis was estimated as release of free fatty acids and by the use of [3H]galactose or [3H]fatty acid-labeled DGDG. Pancreatic juice and duodenal contents hydrolyzed DGDG to fatty acids, digalactosylmonoacylglycerol (DGMG) and water-soluble galactose-containing compounds. The hydrolysis of DGDG was bile salt-dependent and had a pH optimum at 6.5-7.5. Human pancreatic juice released fatty acids from MGDG, DGDG, and SQDG. Purified CEL hydrolyzed all three substrates; the hydrolysis rate was MGDG > SQDG > DGDG. Pure Lip-Col had activity toward MGDG but had little activity against DGDG. Separation of pancreatic juice by Sephadex G100 gel filtration chromatography revealed two peaks with galactolipase activity that coincided with CEL (molecular mass 100 kD) and lipase (molecular mass 50 kD) peaks. In contrast to pure Lip-Col enzymes of the latter peak were as active against DGDG as against MGDG. Thus, DGDG is hydrolyzed both by CEL and by a pancreatic enzyme(s) with a molecular mass of 40-50 kD to fatty acids and lyso DGDG. MGDG, DGDG, and SQDG are all hydrolyzed by human pancreatic juice. Pure CEL hydrolyzed all three substrates.

Topics: Bile Acids and Salts; Carboxylesterase; Carboxylic Ester Hydrolases; Colipases; Dietary Fats; Digestion; Diglycerides; Duodenum; Fatty Acids; Galactolipids; Glycolipids; Humans; Hydrogen-Ion Concentration; Hydrolysis; Lipase; Lipolysis; Pancreas; Pancreatic Juice

We have previously reported that large unilamellar liposomes made from the neutral galactolipid digalactosyldiacylglycerol (DGDG) will aggregate in the presence of monovalent or divalent cations, behavior that would not have been predicted for an uncharged lipid (Webb et al. (1988) Biochim. Biophys. Acta 938, 323-333). In this paper, the effects of including the other major thylakoid lipids on the Mg2+ concentration required for aggregation of DGDG vesicles has been examined. Addition of the neutral, hexagonal-II phase preferring lipid monogalactosyldiacylglycerol (MGDG) to DGDG up to 50 mol% had no effect, suggesting that the MGDG head group is as effective in causing aggregation as the DGDG head group. Addition of 0.5 to 5.0 mol% of either of the two anionic lipids phosphatidylglycerol (PG) or sulfoquinovosyldiacylglycerol (SQDG) inhibited the aggregation of DGDG vesicles, probably by the development of an electrostatic potential. Phosphatidylcholine (PC) in amounts up to 25 mol% did not inhibit or promote aggregation. Vesicles with a composition similar to that of thylakoids (DGDG/MGDG/SQDG/PG, 1:2:0.5:0.5) required 65 mM MgCl2 in the presence of 200 mM KCl, i.e., higher concentrations than are present in the chloroplast stroma. If MGDG made up more than 25 mol% of any combination of lipids, vesicle aggregation could not be reversed by dilution. These results are consistent with cations playing a role in mediating the close approach of bilayers via an effect on head-group hydration and head-group interaction between bilayers.

Topics: Cell Membrane; Diglycerides; Galactolipids; Glycolipids; Lipid Bilayers; Magnesium Chloride; Potassium Chloride