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PubMed1978

Glyceroglucolipids of the human saliva.

Seven individual glycolipids (I--VII) have been isolated from the lipid extract of human saliva. All glycolipids contained glucose, glyceryl ethers and fatty acids, and differed from each other primarily with respect to the number of glucose residues. In addition, glycolipid V contained also the sulfate ester group. The structures of these glycolipids were identified by partial acid and alkaline hydrolysis, oxidation with periodate and chromium trioxide and methylation studies, as: Glc(alpha1 leads to 3)-diglyceride (glycolipid I), Glc(alpha1 leads to 6)Glc(alpha1 leads to 3)-diglyceride (glycolipids II and III), Glc(alpha1 leads to 6)Glc(alpha1 leads to 6)Glc(alpha1 leads to 3)-diglyceride (glycolipid IV), SO3H-6Glc(alpha1 leads to 6)Glc(alpha1 leads to 3)-diglyceride (glycolipid V), Glc(alpha1 leads to 6)Glc(alpha1 leads to 6)Glc(alpha1 leads to 6)Glc(alpha1 leads to 6)Glc(alpha1 leads to 3)-diglyceride (glycolipid VI) and Glc(alpha1 leads to 6)Glc(alpha1 leads to 6)Glc(alpha1 leads to 6)Glc(alpha1 leads to 6)Glc(alpha1 leads to 6)Glc(alpha1 lead to 6)Glc(alpha1 leads to 6)Glc(alpha1 leads to 3)-diglyceride (glycolipid VII). Diglyceride portion of these compounds consists of 1-O-alkyl-2-O-acyl-glycerol with the docosanoate and glyceryl-monodocosyl being the predominant acyl and alkyl components.

Diglycerides↗
PubMed1975

Immunological properties of glycolipids from membranes of Acholeplasma laidlawii.

Glycolipids, the predominant class of lipids in the membranes of Acholeplasma laidlawii, are the haptenic determinants that react with anti-A. Laidlawii serum to fix complement. The predominant complement-fixing activity of the membrane glycolipids was associated with the monoglucoysyl diglyceride, diglucosyl diglyceride, glycerlphosphoryl diglucosyl diglyceride (GPDD), and an unknown lipid B, which did not react with ninhydrin but release glucose and glycerol and traces of phosphorus upon hydrolysis. The glycolipids monoglucosyl diglyceride and diglucosyl diglyceride or GPDD and unknown lipid B were paired as a result of their cross-reactions with selective antisera prepared with the aid of reconstituted membrane complexes containing membrane lipids. Reconstituted membrane complexes assembled from [14C]monoglucosyl diglyceride and delipidated membrane proteins gave optimal complement fixation titers before saturation of the complexes with the ]14C]monoglucosyl diglyceride. The phosphoglycolipid of the membrane, GPDD, was anticomplementary as a pure lipid, a cholesterol liposome, and a reconstituted membrane complex. This anticomplementary activity, which was caused by 3 mug of pure GPDD, affected both human and guinea pig complement. Although human C1, C4, C3, and C5 were not inhibited by GPDD, C2 was inhibited 10-fold by reconstituted membrane complexes containing 150 mug of GPDD. A role for this phosphoglycolipid is discussed in the hypothetical mechanism of inhibition of C2 attachment to SAC1, 4 sites.

Acholeplasma laidlawii↗
PubMed1986

Sustained diacylglycerol formation from inositol phospholipids in angiotensin II-stimulated vascular smooth muscle cells.

Angiotensin II acts on cultured rat aortic vascular smooth muscle cells to stimulate phospholipase C-mediated hydrolysis of membrane phosphoinositides and subsequent formation of diacylglycerol and inositol phosphates. In intact cells, angiotensin II induces a dose-dependent increase in diglyceride which is detectable after 5 s and sustained for at least 20 min. Angiotensin II (100 nM)-stimulated diglyceride formation is biphasic, peaking at 15 s (227 +/- 19% control) and at 5 min (303 +/- 23% control). Simultaneous analysis of labeled inositol phospholipids shows that at 15 s phosphatidylinositol 4,5-bisphosphate (PIP2) and phosphatidylinositol 4-phosphate (PIP) decline to 52 +/- 6% control and 63 +/- 5% control, respectively, while phosphatidylinositol (PI) remains unchanged. In contrast, at 5 min, PIP2 and PIP have returned toward control levels (92 +/- 2 and 82 +/- 4% control, respectively), while PI has decreased substantially (81 +/- 2% control). The calcium ionophore ionomycin (15 microM) stimulates diglyceride accumulation but does not cause PI hydrolysis. 4 beta-Phorbol 12-myristate 13-acetate, an activator of protein kinase C, inhibits early PIP and PIP2 breakdown and diglyceride formation, without inhibiting late-phase diglyceride accumulation. Thus, angiotensin II induces rapid transient breakdown of PIP and PIP2 and delayed hydrolysis of PI. The rapid attenuation of polyphosphoinositide breakdown is likely caused by a protein kinase C-mediated inhibition of PIP and PIP2 hydrolysis. While in vascular smooth muscle stimulated with angiotensin II inositol 1,4,5-trisphosphate formation is transient, diglyceride production is biphasic, suggesting that initial and sustained diglyceride formation from the phosphoinositides results from different biochemical and/or cellular processes.

Angiotensin II↗
PubMed1981

Differential activation of platelet phospholipases by thrombin and ionophore A23187.

Although exposure of platelets to ionophore A23187 causes some activation of phospholipase C, ionophore is an inefficient stimulus for this enzyme. A23187 induces the formation of one-fourth to one-sixth as much diglyceride as does thrombin when comparable amounts of phosphatidylinositol are hydrolyzed. We have shown previously that in the presence of indomethacin thrombin-treated platelets accumulate significant quantitites of diglyceride via inhibition of diglyceride lipase. However, a similar accumulation of diglyceride does not occur when ionophore is used as a stimulus in the presence of indomethacin. Ionophore does not appear to be stimulating the catabolism of diglyceride, since the simultaneous addition of ionophore and thrombin does not impair the formation and metabolism of diglyceride which is promoted by thrombin alone. Further, whereas indomethacin exerts no inhibitory effects upon phospholipase C or the formation of diglyceride in platelets responding to either stimulus, indomethacin does inhibit 1) the loss of arachidonic acid from phosphatidylcholine in response to thrombin and 2) the loss of arachidonic acid from phosphatidylcholine and phosphatidylinositol in response to A23187. We conclude that in A23187-activated platelets, phosphatidylinositol is hydrolyzed primarily by an enzyme other than phospholipase C. This indomethacin-inhibitable enzyme is probably a phospholipase A. Therefore, the full expression of phospholipase C in platelets requires more than a general flux in intracellular calcium.

Anti-Bacterial Agents↗
PubMed1969

Polygalactolipids in spinach chloroplasts.

Two polygalactolipids, designated as components A and B, were isolated from spinach chloroplasts and were also obtained from glycolipid products synthesized with chloroplast enzymes using uridine diphosphate galactose as a galactose donor. These lipids were purified by column and thin layer chromatography. Chemical analysis of component A indicates that the lipid is trigalactosyl diglyceride, whereas component B behaves like tetragalactosyl diglyceride on a thin layer plate. The major fatty acid in trigalactosyl diglyceride was alpha-linolenic acid. Relative amount (molar ratio) of galactolipids in spinach chloroplasts was monogalactosyl diglyceride:digalactosyl diglyceride:trigalactosyl diglyceride:(tetragalactosyl diglyceride) = 60:30:5:1.

Chloroplasts↗
PubMed1991

Metabolism of oleic acid in differentiating BFC-1 preadipose cells.

Incorporation of [3H]oleate and [14C]glucose into cellular lipids was studied in the preadipose cell line BFC-1 to determine flux changes that accompany the adipose conversion process. Dilution of oleate by intracellular fatty acids (FA) was estimated from the 3H/14C incorporation ratios and from relating steady-state radioactivity in diglycerides to their measured cellular levels. The data indicated that exogenous FA mixed with less than 1% of endogenous FA on its pathway to esterification. Conversion of preadipocytes to adipocytes increased uptake of FA and glucose by approximately 3-fold and synthesis of diglycerides and triglycerides by 5- and 16-fold, respectively, with little if any increase of phospholipid synthesis. A 50% drop in 3H/14C incorporation ratio indicated a doubling of the rate at which endogenous FA mixed with the exogenous FA that had entered the cell. Adipocytes compared with preadipocytes exhibited a 50% greater cell diameter and a doubling of intracellular water volume and of protein and phospholipid levels, reflecting cellular enlargement consequent to the arrest of cell division that precedes adipose conversion. Diglyceride levels were also increased in adipocytes, however, since their turnover was fast, as indicated by rapid equilibration of diglyceride labeling; the increase reflected changes in their relative rates of synthesis and disposal. Diglyceride levels related to cell phospholipid, and other indexes of cell size remained constant. This indicated that the supply of diglycerides was tightly coupled to the synthesis of triglycerides and phospholipids, which suggested feedback regulation of diglyceride formation. The studies provide a methodological approach to measurement and interpretation of rates of lipid deposition in cultured cells.

Adipose Tissue↗
PubMed1994

Alpha-thrombin-induced nuclear sn-1,2-diacylglycerols are derived from phosphatidylcholine hydrolysis in cultured fibroblasts.

Diglycerides play an important role in a number of agonist-induced signal transduction pathways. We have recently demonstrated that alpha-thrombin induces a rapid increase in the level of diglyceride mass in the nucleus and a selective increase in nuclear PKC-alpha [Leach, K.L., Ruff, V.A., Jarpe, M.B., Fabbro, D., Adams, L.D., & Raben, D.M. (1992) J. Biol. Chem. 267, 21816-21822]. In the present report, we examined the potential source of the induced nuclear diglycerides by examining the molecular species profiles of both the induced diglycerides and nuclear phospholipids by capillary gas chromatography. The molecular species profiles of the nuclear diglycerides generated resemble the species profiles of PC, and not PI species, at all times. In addition, while our previous data indicated that the molecular species of whole-cell phospholipids did not change in response to alpha-thrombin, nuclear PE was altered in a dramatic and selective manner in response to this agonist. These results demonstrate that PC hydrolysis is the predominant, if not exclusive, source of the alpha-thrombin-induced nuclear diglycerides in these fibroblasts.

Cell Fractionation↗
PubMed1976

Synthesis of biologically active spin-labelled radioactive cytidine diphosphodiglyceride, a novel probe for biological membranes.

A versatile synthesis of spin-labelled radioactive cytidine diphospho-sn-1,2-diacylglycerol (CDP-diglyceride) has been developed based on the combination of the enzymatic acylation of radioactive sn-glycero-3-phosphate with 12-doxyl stearic acid and the chemical conversion of the thus obtained spin-labelled radioactive phosphatidic acid with cytidine monophosphomorpholi-date into spin-labelled radioactive CDP-diglyceride. The method for the isolation and purification of the latter compound was described. This obtained CDP-[2-3H]diglyceride contained 10% of fatty acids of paramagnetic nature, presumably present as a covalently bound 12-doxyl stearic acid esters. The biological activity was tested by using the synthesized compound as a substrate in the mitochondrial biosynthesis of phosphatidylglycerol. It was found that spin-labelled CDP-[2-3H]diglyceride prepared as described can be converted in the presence of sn-[2-14C]-glycero-3-phosphate into a spin-labelled [2-3H, 2'-14C]phosphatidylglycerol with isolated rat liver mitochondria, establishing therefore that the site of its utilization is identical with the site of phosphatidylglycerol synthesis in isolated mitochondria, i.e. inner mitochondrial membrane. Results described demonstrate that the synthesized spin-labelled CDP-diglyceride can be used as a specific probe for the spin- and radioactive covalent labelling of polyglycerophosphatides of mitochondrial membranes. Some implications and further possibilities in the study of biological membranes using the spin-labelled radioactive CDP-diglyceride are discussed.

Animals↗
PubMed1976

Acyl specificity in triglyceride synthesis by lactating rat mammary gland.

We have studied the specificity of the acyl-CoA:diglyceride acyltransferase reaction in lactating rat mammary gland to provide a rational explanation at the enzyme level for the nonrandom distribution of fatty acids in milk fat triglycerides. Acyl-CoA:diglyceride acyltransferase activity was measured using various diglyceride and radioactive acyl-CoA substrates; products were identified as triglycerides by thin-layer and gas-liquid chromatography. Most of the enzymatic activity was located in the microsomal fraction and showed a broad specificity for the acyl donors tested C10, C12, C14, C16, C18, and C18:1 CoA esters). The acyltransferase activity was highly specific for sn-1,2-diglyceride enantiomers; rac-1,3- and sn-2,3-diglycerides were relatively inactive. The acyl-CoA specificity was not affected by the type of 1,2-diglyceride acceptor offered, although dilaurin was the best acceptor and sn-1,2-dilaurin greater than sn-1,2-dimyristin greater than sn-1,2-dipalmitin greater than sn-1,2-distearin. We have previously shown that in the microsomal fraction from lactating rat mammary gland, the acyltransferase activities concerned with the conversion of sn-glycero-3-phosphate to diacylglycerophosphate show a very marked specificity for long chain acyl-CoA's. Therefore, we conclude that the predominant localization of long chain fatty acids in the 1 and 2 positions, and of shorter chain fatty acids in the 3 position of the glycerol backbone, results at least in part from the specificities of the mammary gland acyltransferases.

Acyltransferases↗
PubMed1989

On the biological occurrence and regulation of 1-acyl and 1-O-alkyl-diradylglycerols in human neutrophils. Selective destruction of diacyl species using Rhizopus lipase.

The occurrence and regulation of 1-ether-linked diradylglycerol in human neutrophils were investigated using a sensitive and practical analytical mass method which distinguishes 1-O-alkyl- (EAG) versus 1-acyl (DAG) diglycerides. After phosphorylation of diglycerides to the corresponding [32P]phosphatidic acids using [gamma-32P]ATP and diglyceride kinase (Preiss, J., Loomis, C. R., Bishop, W. R., Stein, R., Niedel, J. E., and Bell, R. M. (1986) J. Biol. Chem. 261, 8597-8600), lipase from Rhizopus arrhizus selectively degraded the 1-acyl-containing species (DAG), but the ether lipid (EAG) was resistant and was identified and quantified after thin layer chromatography separation. By using this method, unstimulated neutrophils were demonstrated to contain both DAG and EAG (100-180 and 40-95 pmol/10(7) cells, respectively). The chemoattractant formyl-methionyl-leucyl-phenylalanine (fMLP) caused a rapid (30 s) and transient increase (1.6-fold) in DAG, but no increase in EAG. Opsonized zymosan produced a 6-8-fold sustained increase in DAG peaking at 2 to 3 min, but only a small (1.7-fold) increase in EAG which was not seen until later times (10 min). Thus, under these stimulation conditions, the major diglyceride was DAG. However, in neutrophils "primed" with cytochalasin B or phorbol ester, formyl-methionyl-leucyl-phenylalanine caused a significant increase in EAG. Neutrophils pretreated with cytochalasin B and then stimulated by fMLP showed a rapid (15-60 s) increase (more than 3-fold) in total diglycerides which was sustained beyond 5 min. At the earliest time points (15-30 s), the increase was due almost entirely to DAG (3-fold), but at 1 min and beyond, EAG comprised as much as 40% of the total (up to a 5-fold increase in EAG). Neutrophils pretreated with phorbol ester prior to fMLP stimulation showed a rapid (around 30 s) more than 2-fold increase in both DAG and EAG. Thus, priming conditions (in particular cytochalasin B) may alter either the access of phospholipase(s) C and/or D to membrane phospholipids or may affect their activities, allowing hydrolysis of 1-O-alkyl-containing lipids to generate 1-O-alkyl-containing diglycerides.

Cytochalasin B↗
PubMed1990

Phospholipase C and diacylglycerol lipase in human gallbladder and hepatic bile.

A phospholipase C in bile, free of bacterial infection, has recently been identified from cholesterol gallstone patients. Because of the importance of phosphatidylcholine in solubilizing cholesterol in bile, this study further investigates the metabolism of phosphatidylcholine in delipidated gallbladder and common bile duct biles. Phospholipase C activity, as measured by the release of phosphoryl[3H]choline from the substrate 1,2-dipalmitoyl-sn-glycero-3-phospho [N-methyl-3H]choline, was identified in both hepatic and gallbladder biles. Similar levels of activity (nmol.h-1.mg-1 of delipidated protein) were found in common bile duct (11.25 +/- 14.23) and gallbladder bile (19.07 +/- 22.24), although per milliliter of bile, the mean gallbaldder levels were 6.4 times greater than those found in common duct bile. With the tow substrates, 1-palmitoyl-2[9,10-3H] palmitoyl-sn-glycero-3-phosphocholine and 1,2(1-14C) dipalmitoyl-sn-glycero-3-phosphocholine, the majority of organically extracted label, after thin-layer chromatography, was recovered as radiolabeled diglyceride, confirming the presence of phospholipase C. Diglyceride levels were found to be closely correlated with [3H]choline (slope, 0.9820; r = 0.9844). In addition to diglyceride, both radiolabeled free fatty acid and monoglyceride were identified in common bile duct and gallbladder biles, although their levels were an order of magnitude less than measurable phospholipase C activity. To determine whether the free fatty acid release was due to either a diacylglycerol-lipase or a phospholipase A2, the effect of adding unlabeled diglyceride on free fatty acid formation from the substrate [14C]DPPC was examined. As the concentration of unlabeled diglyceride was increased, the amount of free fatty acid and monoglyceride released were both reduced in parallel. Direct measurement of diacylglycerol-lipase activity by incubating the diglyceride, sn-2[3H]dipalmitoyl, resulted in release of both products in a ratio similar to that found with sn-2[3H]DPPC. Finally, no radiolabeled lysolecithin was identified with [3H]choline-DPPC or [14C]DPPC as substrate indicating the free fatty acid was the product of a diacylglycerol-lipase rather than a phospholipase A2. Phospholipase C and diacyl-glycerol-lipase activities were significantly correlated (P less than 0.01).(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed2003

Classification of edible oils by employing 31P and 1H NMR spectroscopy in combination with multivariate statistical analysis. A proposal for the detection of seed oil adulteration in virgin olive oils.

A combination of (1)H NMR and (31)P NMR spectroscopy and multivariate statistical analysis was used to classify 192 samples from 13 types of vegetable oils, namely, hazelnut, sunflower, corn, soybean, sesame, walnut, rapeseed, almond, palm, groundnut, safflower, coconut, and virgin olive oils from various regions of Greece. 1,2-Diglycerides, 1,3-diglycerides, the ratio of 1,2-diglycerides to total diglycerides, acidity, iodine value, and fatty acid composition determined upon analysis of the respective (1)H NMR and (31)P NMR spectra were selected as variables to establish a classification/prediction model by employing discriminant analysis. This model, obtained from the training set of 128 samples, resulted in a significant discrimination among the different classes of oils, whereas 100% of correct validated assignments for 64 samples were obtained. Different artificial mixtures of olive-hazelnut, olive-corn, olive-sunflower, and olive-soybean oils were prepared and analyzed by (1)H NMR and (31)P NMR spectroscopy. Subsequent discriminant analysis of the data allowed detection of adulteration as low as 5% w/w, provided that fresh virgin olive oil samples were used, as reflected by their high 1,2-diglycerides to total diglycerides ratio (D > or = 0.90).

Analysis of Variance↗
PubMedDate not supplied

Effect of liposomes on substrate uptake by isolated guinea-pig liver mitochondrial and microsomal membranes.

The effect of adding small unilamellar lecithin liposomes, prepared in the presence of cytidine-diphosphoryl-1,2-diglycerides (CDP-diglycerides) or cytochrome c, on microsomal biosynthesis of phosphatidylinositol and NADPH-cytochrome c reduction and on mitochondrial biosynthesis of polyglycerophosphatides and succinate-cytochrome c reduction was studied in isolated guinea-pig liver subcellular membranes. Both microsomal biosynthesis of phosphatidylinositol and mitochondrial biosynthesis of phosphatidylglycerol were significantly reduced when CDP-diglycerides associated with liposomes were used, suggesting that some CDP-diglycerides were entrapped by liposomal membranes and were not available to subcellular membranes as substrates. The degree of decrease in phospholipid biosynthesis depended on the membrane and the nature of fatty acids in CDP-diglycerides. The composition of mitochondrial polyglycerophosphatides synthesized in the presence of CDP-diglycerides-liposomes was also affected in respect to the amount of phosphatidylglycerol formed. The reduction of cytochrome c in both microsomal and mitochondrial membranes was also decreased when liposomes were present in the assay system, but to a lesser degree than the phospholipid biosynthesis. These results indicate that the cytochrome c liposome association did not provide efficient protection of this substrate from the subcellular reduction. When chlorpromazine was also present with liposomes in the assay system, the NADPH-cytochrome c reduction in microsomes was scarcely affected, while the succinate-cytochrome c reduction in mitochondria was dependent on the concentration of chlorpromazine and could be completely abolished. These results were interpreted in terms of liposomal interaction with substrates in competition with subcellular membranes for the same substrates.

Animals↗
PubMed1991

Epidermal growth factor-induced hydrolysis of phosphatidylcholine by phospholipase D and phospholipase C in human dermal fibroblasts.

The enzymatic pathways for formation of 1,2-diradylglyceride in response to epidermal growth factor in human dermal fibroblasts have been investigated. 1,2-Diradylglyceride mass was elevated 2-fold within one minute of addition of EGF. Maximal accumulation (4-fold) occurred at 5 minutes. Since both diacyl and ether-linked diglyceride species occur naturally and may accumulate following agonist activation, we developed a novel method to determine separately the alterations in diacyl and ether-linked diglycerides following stimulation of fibroblasts with EGF. Utilizing this method, it was found that approximately 80% of the total cellular 1,2-diradylglyceride was diacyl, the remaining 20% being ether-linked. Addition of EGF caused accumulation of 1,2-diacylglyceride without alteration in the level of ether-linked diglyceride. Thus, the observed induction of 1,2-diradylglyceride by EGF was due exclusively to increased formation of 1,2-diacylglyceride. In cells labelled with [3H]choline, the water soluble phosphatidylcholine hydrolysis products, phosphorylcholine and choline, were increased 2-fold within 5 minutes of addition of EGF. No hydrolysis of phosphatidylethanolamine, phosphatidylserine, or phosphatidylinositol was observed. Quantitation by radiolabel and mass revealed equivalent elevations in phosphorylcholine and choline, suggesting stimulation of both phospholipase C and phospholipase D activities. To identify the presence of EGF-induced phospholipase D activity, cells were labelled with exogenous [3H]1-0-hexadecyl, 2-acyl phosphatidylcholine and its conversion to phosphatidic acid in response to EGF determined. Radiolabelled phosphatidic acid was detectable in 15 seconds after addition of EGF and was maximal (3-fold) at 30 seconds. Consistent with the presence of EGF-induced phospholipase D activity, treatment of cells with EGF, in the presence of [14C]ethanol, resulted in the rapid formation of [14C]phosphatidylethanol, the product of phospholipase D-catalyzed transphosphatidylation. The formation of phosphatidylethanol, which competes for the formation of phosphatidic acid by phospholipase D, did not diminish the induction of 1,2-diglyceride by EGF. These data suggest that the phosphatidic acid formed by phospholipase D-catalyzed hydrolysis of phosphatidylcholine is not a major precursor of the observed increased 1,2-diglyceride. Thus, the induction of 1,2-diacylglycerol by EGF may occur primarily via phospholipase C-catalyzed hydrolysis of phosphatidylcholine.

Cells, Cultured↗
PubMed1993

Phospholipase D and exocytosis of the ram sperm acrosome.

We have investigated whether phospholipase D (PLD) is involved in events leading to acrosomal exocytosis. Ram spermatozoa pre-labelled with [3H]alkyl-lysophosphatidylcholine and stimulated with the ionophore A23187 (1 microM) and Ca2+ (3 mM) in the presence of ethanol, showed a slow time-dependent increase in [3H]phosphatidic acid and [3H]phosphatidylethanol (PEt), the latter being clear evidence of PLD activity. Unlabelled cells similarly treated underwent acrosomal exocytosis. However, [3H]PEt formation was inhibited by high Ca2+ concentrations, although such conditions result in maximal acrosomal exocytosis. Treatment with A23187/Ca2+ led to a fast generation of [3H]alkyl-diglyceride and an increase in 1,2-diacylglycerol mass, which preceded [3H]PEt formation. The rises in [3H]alkyl-diglyceride and 1,2-diacylglycerol mass took place regardless of the presence or absence of ethanol. Inclusion of propranolol, a phosphatidic acid phosphohydrolase inhibitor, did not affect the early rise of labelled or unlabelled 1,2-diglycerides either. Stimulation of spermatozoa with A23187/Ca2+ in the presence of either ethanol or propranolol did not affect the occurrence of acrosomal exocytosis. Taken together, these results indicate that although Ca2+ entry triggers a late activation of PLD, this enzyme is not involved in the early generation of diglycerides. Moreover, they suggest that PLD does not make a substantial contribution in events leading to exocytosis of the sperm acrosome. Therefore, generation of diglycerides may take place primarily via phospholipase C.

Acrosome↗
PubMed1991

Source and role of diacylglycerol formed during phagocytosis of opsonized yeast particles and associated respiratory burst in human neutrophils.

The results presented in this paper demonstrate that in human neutrophils phagocytosis of C3b/bi and IgG-opsonized yeast particles is associated with activation of phospholipase D and that this reaction is the main source of diglycerides. The demonstration is based upon the following findings: 1) the challenge of neutrophils with these opsonized particles was followed by a rapid formation of [3H]alkyl-phosphatidic acid [( 3H]alkyl-PA) and [3H]alkyl-diglyceride [( 3H]alkyl-DG) in cells labeled with [3H]alkyl-lyso-phosphatidylcholine; 2) in the presence of ethanol [3H]alkyl-phosphatidylethanol was formed, and accumulation of [3H]alkyl-PA and [3H]alkyl-DG was depressed; 3) propranolol, by inhibiting the dephosphorylation of [3H]alkyl-PA, completely inhibited the accumulation of [3H]alkyl-DG and depressed by about 75% the formation of diglyceride mass. Evidence is also presented that phagocytosis of C3b/bi and IgG-opsonized yeast particles and associated respiratory burst can take place independently of diglyceride formation and of the activity of this second messenger on protein kinase C. In fact: a) propranolol while completely inhibited the formation of diglyceride mass did not modify either the phagocytosis or respiratory burst; b) these two processes were insensitive to staurosporine.

Alkaloids↗
PubMed1990

Modulation by neuropeptides of bradykinin-stimulated second messenger release in dorsal root ganglion neurons.

Fetal rat dorsal root ganglion neurons (7-8 days in culture) were labeled with [3H]arachidonic acid for 24 h. Stimulation with 10 microM bradykinin (BK) for 30 s resulted in nearly 2-fold increases in levels of radioactive diglyceride and arachidonic acid. A similar result was obtained in the absence of receptor stimulation using the Ca2+ channel agonist BAY K 8644 (10 microM, in the presence of 100 mM potassium chloride) or the Ca2+ ionophore, ionomycin (2.5 microM). If Ca2+ influx was inhibited by adding 3 mM Co2+, a blocker of voltage-sensitive calcium channels, or 2.5 mM EDTA, then BK-stimulated accumulation of both arachidonate and diglyceride was inhibited. These data suggest Ca2+ influx is required for ligand-stimulated accumulation of both arachidonate (a product of diglyceride-lipase or phospholipase A2) and diglyceride (a product of phospholipase C). Two distinct populations of channels may be involved in these reactions since pretreatment with 10 microM nifedipine or 50 microM verapamil (agents which block a subset of voltage-sensitive Ca2+ channels) inhibited BK-stimulated accumulation of arachidonic acid, but did not inhibit diglyceride accumulation. Such functional discrimination appears to have physiological importance; the inhibitory effect of nifedipine and verapamil on BK-stimulated arachidonate release was mimicked by pretreatment with peptides which decrease Ca2+ channel conductance in dorsal root ganglion neurons. The three peptides used were 1 microM neuropeptide Y, 10 microM somatostatin, and 10 microM [N-MePhe3,D-Pro4]-morphiceptin. The effect of neuropeptide Y was blocked by pretreatment with pertussis toxin.(ABSTRACT TRUNCATED AT 250 WORDS)

Analgesics↗
PubMed1983

Neutral lipids of frog and rat rod outer segments.

Neutral lipids of rod outer segments (ROS) from frog and rat comprise roughly 10 mol% of the total lipids and consist of free sterol, free fatty acids, and 1,2-diglycerides, but contain no detectable sterol esters or triglycerides. Expressed as nmol per mg ROS protein, the levels of both free fatty acids and free sterol are higher in the rat than in the frog, whereas the diglycerides in frogs are about four times higher than in rats. The level of 22:6 omega 3 in the free fatty acids fraction of the frog is twice that of the rat, although the level of 22:6 omega 3 in both the frog and rat free fatty acids is lower than in any of the glycerolipids. The diglyceride fraction from both animals consists almost entirely of two molecular species: in the frog, the C-38 and C-40 type predominate in a molar distribution of 52 and 42% respectively, whereas in the rat, the C-36 and C-38 types are most abundant in a molar distribution of 28 and 60%, respectively. Comparison of the diglyceride fatty acid and molecular species compositions with those of phosphatidylinositol and phosphatidic acid led to the suggestion that ROS diglycerides are derived from phosphatidylinositol.

Animals↗