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PubMed1978

Neutral lipid accumulation in the membranes of Escherichia coli mutants lacking diglyceride kinase.

We have developed a rapid autoradiographic screening assay for detecting diglyceride kinase in colonies of Escherichia coli and have isolated four strains lacking this enzyme. The gene (designated dgk) which is altered in these mutants is cotransduceable with the malB locus, near minute 90 on the chromosome. The membranes of strain RZ60 (which carries the dgk-6 lesion) contain substantial amounts of 1,2-diglyceride, representing approximately 8% of the total lipid. In contrast, wild type cells of E. coli (dgk+) only contain about 0.5% 1,2-diglyceride. The phospholipid composition of these mutants is not dramatically altered, and they are not temperature sensitive for growth. However, strains bearing the dgk-6 mutation do not grow well on nutrient media of low osmolarity. This can be corrected by the inclusion of 1% NaCl or 0.5 M sucrose. These results suggest that 1,2-diglyceride is the true substrate for the kinase in vivo and that the kinase functions as a minor route for phosphatidic acid synthesis. Genetic modification of the diglyceride content of the E. coli membrane has not been reported previously.

Autoradiography↗
PubMed1989

[Effect of diglyceride on phospholipase A2 activities in plasma membrane of guinea pig peritoneal macrophases].

The AA release from phospholipids is believed to be controlled by the activation of phospholipase A2 which are probably localized in the plasma membranes. And the considerable interest has been focused on the study of cells of the immune system including macrophages which metabolize arachidonic acid (AA) to prostaglandins, thromboxanes and leukotriens. Recently, it has been reported that phosphatidylinositol (PI) turnover plays an important role in the response to external stimuli in these cells. PI turnover has been accepted as being initiated by the hydrolysis of PI which is catalyzed by the phospholipase C and produced AA. Recently, we demonstrated that PI-specific phospholipase A2 in macrophage plasma membrane directly acted for AA release from PI. On the other hand, diglyceride, which is produced from PI by phospholipase C activation, is known to regulate the several cell functions with a protein kinase C activation. In this report, we examined the effect of diglyceride on phospholipase A2 activities in macrophage plasma membrane. PI-phospholipase A2 and PC-phospholipase A2 activities were stimulated by the addition of diglyceride. In contrast, PE-phospholipase A2 was not affected by diglyceride addition. The results suggested that phospholipase A2 activation was occurred with coupling the diglyceride production via the phospholipase C pathway.

Arachidonic Acid↗
PubMed1989

Activation of protein kinase C by naturally occurring ether-linked diglycerides.

Recent studies have demonstrated that ether-linked diglycerides are endogenous constituents of biologic tissues and accumulate during agonist stimulation (Daniel, L. W., Waite, M., and Wykle, R. L. (1986) J. Biol. Chem. 261, 9128-9132) and myocardial ischemia (Ford, D. A., and Gross, R. W. (1989) Circ. Res. 64, 173-177). Although protein kinase C previously had been thought to specifically require 1,2-diacyl-sn-glycerol (DAG) molecular species for activation, the present study demonstrates that purified rat brain protein kinase C is activated by naturally occurring ether-linked diglycerides (e.g. 1-O-hexadec-1'-enyl-2-octa-dec-9'-enoyl-sn-glycerol and 1-O-hexadecyl-2-octa-dec-9'-enoyl-sn-glycerol) with a similar dose response curve to that for DAG molecular species. Although in vitro assays demonstrated that DAG could partially activate protein kinase C in the absence of free calcium, activation by ether-linked diglycerides required free calcium concentrations found only in stimulated cells (greater than 1 microM [Ca2+]free). To substantiate these findings the alpha and beta isoforms of protein kinase C from rat brain cortical grey matter were resolved by hydroxylapatite chromatography. Although the beta isoform of protein kinase C was substantially activated by DAG in the absence of free calcium, activation by ether-linked diglycerides had an absolute requirement for physiologic increments in free calcium ion found in stimulated cells. Since ether lipids are localized in specific subcellular membrane compartments, accumulate during several pathophysiologic perturbations and are effective activators of protein kinase C with separate and distinct calcium requirements in comparison to DAG, these results suggest that ether-linked diglycerides are important and potentially specific biologic activators of one or more isoforms of protein kinase C.

Animals↗
PubMed1994

Attenuation of ceramide-induced apoptosis by diglyceride in human myeloid leukemia cells.

Prior studies demonstrated that increased intracellular availability of ceramide induces apoptotic DNA degradation and cell death in the human leukemia cell lines HL-60 and U937 (Jarvis, W. D., Kolesnick, R. N., Fornari, F. A., Traylor, R. S., Gewirtz, D. A., and Grant, S. (1994) Proc. Natl. Acad. Sci. U. S. A. 91, 73-77). The present findings show that diglyceride opposes ceramide-related apoptosis in HL-60 and U937 cells. Acute (6-12-h) exposure to sphingomyelinase (100 milliunits/ml) or synthetic ceramide (10 microM) promoted apoptotic degradation of genomic DNA as indicated by (a) the appearance of both approximately 50-kilobase pair (kbp) DNA fragments and approximately 0.2-1.2-kbp DNA fragment ladders on agarose gels, (b) formation and release of small double-stranded DNA fragments, and (c) loss of integrity of bulk DNA. DNA damage was associated with reduced clonogenicity and expression of apoptotic morphology. In contrast, exposure to phospholipase C (0.001-100 milliunits/ml) or synthetic diglyceride (10 microM) failed to promote apoptosis and abolished the lethal actions of ceramide as defined by each of the indices outlined above. Ceramide-related apoptosis was also reduced by acute (6-h) exposure to tumor promoters such as phorbol dibutyrate and mezerein and the non-tumor-promoting agent bryostatin 1; conversely, chronic (24-h) pretreatment with these agents failed to modify ceramide-mediated cytotoxicity, but abolished the protective actions of diglyceride. These findings demonstrate that diglyceride and pharmacological protein kinase C activators reduce or abolish ceramide-mediated apoptosis in human leukemia cells and support the concept of a cytoprotective function for protein kinase C in the regulation of leukemic cell survival. In addition, the capacity of diglyceride to prevent very early genomic lesions (e.g. generation of 50-kbp DNA fragments) suggests that acute activation of protein kinase C arrests apoptosis at an initial stage.

Apoptosis↗
PubMed1983

RHC 80267 does not inhibit the diglyceride lipase pathway in intact platelets.

RHC 80267 inhibits diglyceride lipase activity in microsomes from canine platelets (1). Chau and Tai (2) reported that RHC 80267 prevents the transient accumulation of monoglyceride in thrombin-stimulated human platelets, while leaving arachidonate release unimpaired. In contrast, we find that while the drug inhibits both diglyceride lipase (I50 = 15 microM) and monoglyceride lipase (I50 = 11 microM) activities in platelet microsomes, it is ineffective when added to intact platelets. The transient intermediates in the diglyceride lipase pathway, 1,2-diglyceride and 2-monoglyceride, both accumulated after thrombin stimulation of intact platelets treated with RHC 80267, and arachidonate release was not inhibited. We conclude that RHC 80267 cannot be used to evaluate the diglyceride lipase pathway in intact platelets.

Arachidonic Acid↗
PubMed1971

The diglyceride kinase of rat cerebral cortex.

1. Formation of phosphatidic acid by diglyceride kinase (EC 2.7.1.-) in the presence of ATP and Mg(2+) was shown in a homogenate and subcellular fractions of rat cerebral cortex. 2. The kinase was activated by Mg(2+). Ca(2+) activated to a smaller extent but was inhibitory in the presence of optimum concentration of Mg(2+). Activity was greatly increased in the presence of added 1,2-diglyceride. 3. Sodium deoxycholate markedly stimulated the reaction, but other detergents (Cutscum and Triton X-100) did not. 4. Diglyceride kinase was concentrated in the supernatant and microsomal fractions from rat cerebral cortex. The distribution of the kinase in the particulate fractions resembled that of acetylcholinesterase and 5'-nucleotidase. 5. The rate of phosphatidic acid synthesis by the diglyceride kinase route was much greater than reported rates for acylation of 3-glycerophosphate and was also very rapid in comparison with the rates of other steps in the synthesis of phosphoinositides. 6. Acetylcholine had no stimulatory effect on diglyceride kinase of isolated intact nerve-ending particles or of nerve-ending membranes obtained after osmotic shock.

Acetylcholine↗
PubMed1992

Antiviral nucleoside diphosphate diglycerides: improved synthesis and facilitated purification.

Cytidine diphosphate diglyceride and its analogs have previously been synthesized by condensing phosphatidic acid with the monophosphomorpholidates of the various nucleosides. Yields have been low and purification of the product has been difficult. We report here an improved method for the synthesis of nucleoside diphosphate diglycerides with potential antiviral activity. Phosphatidic acid was activated with morpholine in the presence of dicyclohexylcarbodiimide to phosphatidic acid morpholidate. This compound was condensed with the 5'-monophosphate of the anti-HIV agents 3'-azido-3'-deoxythymidine, 3'-deoxythymidine or 2',3'-dideoxycytidine, and the monophosphate of the anti-HSV agent acyclovir. The resulting nucleoside diphosphate diglycerides are potential candidates for improved antiviral action when compared to the parent nucleoside analogs. Compared to the older method for the preparation of cytidine diphosphate diglyceride and analogs thereof, the new method has several advantages: reaction times are reduced from several days to several hours and the yield of the reactions is generally increased from 20-40% to between 50 and 80%. In addition, the purification of the compounds is greatly facilitated due to the small amount of phosphatidic acid remaining in the reaction mixture.

Acyclovir↗
PubMed1975

Further studies on the formation of cardiolipin and phosphatidylglycerol in rat liver mitochondria. Effect of divalent cations and the fatty acid composition of CDP-diglyceride.

The divalent cation requirement for mitochondrial cardiolipin biosynthesis has been further investigated. The relative order of divalent cation activity was Co-2+ greater than Mn-2+ greater than Mg-2+. Cardiolipin was not formed in the incubations with Zn-2+, Fe-2+, Cu-2+, Hg-2+, and Ca-2+. Cardiolipin synthesis in the presence of optimal cincentration of Co-2+ was inhibited by Ca-2+. A series of CDP-diglycerides was synthesized having differences in fatty acid chain lenth and degree of unsaturation. These compounds were tested in mitochondrial cardiolipin and phosphatidylglycerol synthesis. Although there were some minor differences between phosphatidylglycerol and cardiolipin synthesis, in general, saturated shorter chain CDP-diglycerides (dilauroyl and dimyristoyl) were better substrates than the longer chain dipalmitoyl and distearoyl homologues. Introduction of double bonds into distearoyl CDP-diglyceride resulted in more rapid rates of synthesis (e.g. dioleoyl and dilinoleoyl CDP-diglyceride). Significance of the results is dicussed with regard to possible mechanisms of linoleic acid incorporation into rat liver cardiolipin.

Animals↗
PubMed1976

A versatile, flexible synthesis of 1,3-diglycerides and tryglycerides.

A flexible method for synthesising 1,30diflycerides and triglycerides is described. Glycidol esters, prepared by a known route from epichlorohydrin and the sodium salt of a fatty acid, were heated with another or with the same fatty acid and a quaternary ammonium salt. This resulted in a fast, mild reaction and higher yields and greater purity of the diglycerides than hitherto obtained in this synthesis. The mixture of 1,3- and 1,2-diglycerides obtained was isomerised by heating while still in the solid phase to 1,3-diglycerides. Triglycerides were prepared from the diglycerides by acylation using a fatty acid chloride and pyridine in hexane.

Chemical Phenomena↗
PubMed2001

A novel class of oxylipins, sn1-O-(12-oxophytodienoyl)-sn2-O-(hexadecatrienoyl)-monogalactosyl Diglyceride, from Arabidopsis thaliana.

The cyclic derivative of 13(S)-hydroperoxolinolenic acid, 12-oxophytodienoic acid, serves as a signal transducer in higher plants, mediating mechanotransductory processes and plant defenses against a variety of pathogens, and also serves as a precursor for the biosynthesis of jasmonic acid, a mediator of plant herbivore defense. Biosynthesis of 12-oxophytodienoic acid from alpha-linolenic acid occurs in plastids, mainly in chloroplasts, and is thought to start with free linolenic acid liberated from membrane lipids by lipase action. In Arabidopsis thaliana, the glycerolipid fraction contains esterified 12-oxophytodienoic acid, which can be released enzymatically by sn1-specific, but not by sn2-specific, lipases. The 12-oxophytodienoyl glycerolipid fraction was isolated, purified, and characterized. Enzymatic, mass spectrometric, and NMR spectroscopic data allowed us to establish the structure of the novel oxylipin as sn1-O-(12-oxophytodienoyl)-sn2-O-(hexadecatrienoyl)-monogalactosyl diglyceride. The novel class of lipids is localized in plastids. Purified monogalactosyl diglyceride was not converted to the sn1-(12-oxophytodienoyl) derivative by the combined action of (soybean) lipoxygenase and (A. thaliana) allene oxide synthase, an enzyme ensemble that converts free alpha-linolenic acid to free 12-oxophytodienoic acid. When leaves were wounded, a significant and transient increase in the level of (12-oxophytodienoyl)-monogalactosyl diglyceride was observed. In A. thaliana, the major fraction of 12-oxophytodienoic acid occurs esterified at the sn1 position of the plastid-specific glycerolipid, monogalactosyl diglyceride.

Arabidopsis↗
PubMed1976

Diglyceride kinase activity of microtubules. Characterization and comparison with the protein kinase and ATPase activities associated with vinblastine-isolated tubulin of chick embryonic muscles.

Vinblastine-isolated microtubule protein from chick embryonic muscles has an enzymatic activity which catalyzes the formation of phosphatidic acid from diglycerides and ATP. The pH optimum (6.4), sedimentation on sucrose gradients (Mr = 85 000), and sensitivity to ions of this diglyceride kinase activity are different to those of a similar enzymatic activity present in 150 000 X g supernatants of chick embryonic muscle homogenates, suggesting that it is a different species which is associated specifically with the microtubules. The reaction requires a divalent ion (e.g. 0.4 mM Mg2+ gives half-maximal stimulation), and GTP can replace ATP rather effectively, especially at nucleotide concentrations lower than 50 muM. The sedimentation of the diglyceride kinase on sucrose gradients coincides with that of the microtubules-associated protein kinase (Mr = 75 000); the heat-stability and sensivitity to proteolysis of both activities are also very similar. Stimulation of one reaction by the addition of the corresponding exogenous substrate does not impair the phosphorylation of the other, and no radioactivity is lost from phosphatidic acid or the protein moiety upon incubation of pre-labelled microtubules with a large excess of unlabelled ATP or GTP. In addition to diglyceride and protein kinase activities (0.2 and 0.3 nmol 32P-transferred X min-1 X mg-1 microtubular protein, respectively), microtubules also contain an associated ATPase (2.8 nmol X min-1 X mg-1), which requires either Mg2+ or Ca2+, can hydrolyze GTP quite effectively, and sediments with a molecular weight of 95000. The results obtained are discussed in connection with the possible relationships existing among these enzymatic activities, as well as their probable role in microtubular functions.

Adenosine Triphosphatases↗
PubMed1980

Synthesis of molecular species of glycerophospholipids from diglyceride-labeled brain microsomes.

Selectivity of CDP-choline:diacylglycerol choline phosphotransferase and CDP-ethanolamine:diacylglycerol ethanolamine phosphotransferase for molecular species of diglyceride has been studied in rat brain microsomes in vitro. Diglyceride-labeled microsomes were prepared by incubation with labeled sn-glycerol-3-phosphate; the microsomes were then incubated with CDP-choline or CDP-ethanolamine for different time intervals. Experimental data extrapolated to zero-time incubation were taken into account for evaluating species specificity. A small selectivity for diglyceride species has been demonstrated for the choline phosphotransferase, but the ethanolamine phosphotransferase was found to convert hexaenoic diglyceride into phospholipid at the highest rate.

Animals↗
PubMed1982

The formation of diarachidonyl diglyceride by rat neutrophils.

Neutrophils isolated from the pleural cavity of rats 3 hr after the intrapleural injection of carrageenan metabolize exogenously added arachidonic acid via cyclooxygenase and lipoxygenase. In addition, these cells esterify arachidonic acid to produce diarachidonyl diglyceride. The structure of the diglyceride was determined with the use of various chemical and enzymatic digestions, gas chromatography-mass spectrometry, and 252Cf plasma-desorption mass spectrometry. The formation of this unique diglyceride is stimulated by the presence of nonsteroidal anti-inflammatory drugs. Some of the possible consequences of diarachidonyl diglyceride production are discussed.

Animals↗
PubMedDate not supplied

Gas chromatographic determination of mono- and diglycerides in fats and oils: summary of collaborative study.

A collaborative study was conducted on a capillary gas chromatographic method for the determination of mono- and diglycerides in fats and oils. Other components of fats and oils such as glycerol, fatty acids, and sterols may be analyzed by this method. Six materials used in the study consisted of 2 commercial mono- and diglyceride emulsifiers, 2 synthetic compositions with known amounts of mono- and diglycerides in the presence of an excess of triglycerides, and 2 refined sunflower oils spiked with mono- and diglycerides. Eight laboratories participated in the study. On the basis of the collaborative study results, the method has been adopted first action by AOAC INTERNATIONAL as an IU-PAC/AOCS/AOAC method.

Chromatography, Gas↗
PubMed1987

Effects of RHC 80267, a diglyceride lipase inhibitor, on prolactin secretion and calcium uptake in GH3 pituitary cells.

The effect of the diglyceride lipase inhibitor RHC 80267 on the prolactin secretory process was examined in clonal anterior pituitary GH3 cells. This compound reduced basal prolactin secretion as well as secretion induced by TRH and phospholipase C but not that induced by phorbol myristate acetate. Although exogenous phospholipase C increased diglyceride, no increase in the products of diglyceride lipase was detected. Moreover, low doses of RHC 80267 were observed to effectively block potassium-stimulated 45calcium influx. It is unlikely that RHC 80267 inhibits prolactin release solely by inhibiting diglyceride lipase. These data suggest blockade of plasma membrane calcium channels as an alternate mechanism for the inhibitory actions of RHC 80267 on intact GH3 cells. These observations may have implications for RHC 80267 action in other cell types.

Animals↗
PubMed1969

The isolation and characterization of trigalactosyl diglyceride from potato tubers.

Trigalactosyl diglyceride has been isolated from tubers of potato (Solanum tuberosum) by a combination of chromatographic methods. This galactolipid, which constitutes approximately 1% by weight of the total lipids, was characterized by analysis of the intact lipid and its deacylation product. The fatty acids:glycerol:galactose molar proportions were shown to be close to 2:1:3. Evidence was obtained that suggests that trigalactosyl diglyceride is a higher homologue of mono- and di-galactosyl diglycerides and contains an additional d-galactopyranosyl moiety that is linked alpha-(1-->6) to the terminal galactose unit of digalactosyl diglyceride.

Chromatography↗
PubMed1987

Renal phospholipase C and diglyceride lipase activity in spontaneously hypertensive rats.

Phospholipase C activity and diglyceride lipase activity were studied in the renal cortex and medulla of 10- and 40-week-old stroke-prone spontaneously hypertensive rats (SHRSP) and age-matched normotensive Wistar-Kyoto rats (WKY). Enhanced phospholipase C activity was found in the cortical and medullary cytosol of kidney from SHRSP, and microsomal diglyceride lipase in SHRSP also increased. In SHRSP, phospholipase C and diglyceride lipase activities increased with age, but this increase was not evident in WKY. Phospholipase C had high substrate specificity for phosphatidylinositol in renal cytosol of both WKY and SHRSP. The increased activities were accompanied by prostaglandin E2 synthesis in renal medullary microsomes of 10-week-old SHRSP and were also present in the kidney of 40-week-old SHRSP. Total phospholipid and arachidonic acid contents in kidney were markedly high in the medulla of 10-week-old SHRSP, but these lipids were decreased in 40-week-old SHRSP. These results suggest that phospholipids and arachidonic acid in SHRSP may be genetically high and that the activated phospholipase C and diglyceride lipase hydrolyze phospholipids, providing arachidonic acid for prostaglandin synthesis, which results in a decrease of phospholipids and arachidonic acid in the kidney of 40-week-old SHRSP. These studies demonstrate that a phosphatidylinositol-specific phospholipase C-prostaglandin synthetic system may play an important role in the course of hypertension in SHRSP.

Animals↗
PubMed1966

Enzymatic synthesis of cytidine diphosphate diglyceride.

Evidence is presented for the enzymatic formation of cytidine diphosphate diglyceride in microsomal preparations from guinea pig liver according to the reaction: CTP + phosphatidic acid right harpoon over left harpoon CDP-diglyceride + p-O-P. Conditions have been found in which the incorporation of labeled CTP into CDP-diglyceride is almost entirely dependent upon added phosphatidic acid. The incorporation of CMP into lipid is very slight. A substantial net synthesis of CDP-diglyceride takes place under these conditions. Some properties of the enzyme system are described.

Animals↗