Showing papers on "Diacylglycerol kinase published in 1980"

Enzymes of glycerolipid synthesis in eukaryotes.

Abstract: INTRODUCfION AND PERSPECfIVES ... ... 460 FATTY ACID ACTIVATION . . . . ..... . .. . . . . . . . . . . .. . .. . . . . . . . .. . .. .. . .. . 463 BIOSYNTHESIS OF PHOSPHATIDIC ACID .... ......... 464 Acylation of Glycerol-P • 464 Acylation of Lysophosphatidic Acid 465 Dihydroxyacetone-P Pathway 466 Diacylglycerol Kinase 467 BIOSYNTHESIS OF DIACYLGLYCEROL 468 BIOSYNTHESIS OF TRIACYLGL YCEROL ......... 469 BIOSYNTHESIS OF PHOSPHATIDYLCHOLINE AND . PHOSPHATIDYLETHANOLAMINE.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470 Choline and Ethanolamine Kinases 470 Choline-P and Ethanolamine-P Cytidyltransferases 470 Cholineand Ethanoiaminephosphotransferases 471 Phosphatidylethanolamine N-methyltransferases 472 BIOSYNTHESIS OF CDP-DIACYLGL YCEROL AND THE ANIONIC PHOSPHOGLYCERIDES .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . .. . .. ... . . . . . . 473 Biosynthesis of Phosphatidylglycerol and Cardiolipin 474 Biosynthesis of Phosphatidylinositol 474 Biosynthesis of bis-Monoacylglyc erol-P 474 PHOSPHOGLYCERIDE MODIFICATION REACfIONS 475 Base Exchange Reactions 475 Reacyiation Reactions 475

Membrane lipids in the pathogenesis of brain edema: phospholipids and arachidonic acid, the earliest membrane components changed at the onset of ischemia.

Abstract: This chapter reviews studies concerning cellular membranes in the pathogenesis of cerebral edema. The main topics discussed are membrane lipids and the observation that the concentration of endogenous free fatty acids increases rapidly and reversibly in the brain after a single electroconvulsive shock. This change suggests that an active deacylation takes place. In addition, brief periods of ischemia trigger a strikingly high production of free fatty acids not from triacylglycerol breakdown but likely arising from membrane lipids. Since cellular membrane damage takes place during the early stages of edema either in neural or endothelial cells, the described changes may be involved in the pathogenesis of brain edema. The free fatty acid production is a unique property of the mature brains of rat, mouse, and monkey. It predominates in gray matter as compared to white matter. The rate of production during early ischemia is comparable to that observed in adipose tissue under maximal hormonal stimulation. In newborn mammalians, as in brains of mature poikilotherms, rates of production during early ischemia are low. The involvement of inositol lipids in the process is suggested since stearic and arachidonic acid are not only produced as free fatty acids but are also acylated in diacylglycerol during the first few minutes of rat and mouse brain ischemia. Prostaglandins and their metabolites of free arachidonic acid, at least during the first 4 to 5 min of ischemia when the rate of production is linear. Harmful membrane effects of lipid peroxides are also discussed.

Stimulus–secretion coupling in rabbit neutrophils is not mediated by phosphatidylinositol breakdown

Abstract: In common with other cells which use intracellular Ca2+ to mediate specific cell function, when rabbit neutrophils are stimulated with specific agonists the rate of metabolism of phosphatidylinositol (PI) increases. This is normally measured as the incorporation of radioactive phosphate or inositol into PI, but these reactions are presumed to be secondary processes following the initial breakdown of pre-existing PI to diacylglycerol. The radioactive labels are incorporated during the stepwise resynthesis of PI via phosphatidic acid (PA). It has been suggested that in the sequence of biochemical events, starting with the binding of the ligand to a receptor, and finally resulting in the expression of cellular activity, the breakdown of PI is an early event immediately directed by activation of the receptor. This could then control the increase in cytoplasmic Ca2+ and other processes dependent on this. Here we report an analysis of the temporal relationship between these phospholipid changes and cell stimulation. Our evidence suggests that in neutrophils, PI breakdown and PA labelling are both consequences and not causes of a rise in intracellular Ca2+.

The inhibition and activation of Ca2+-dependent phosphatidylinositol phosphodiesterase by phospholipids and blood plasma.

Abstract: 1. Phosphatidylinositol-phosphodiesterase (EC 3.1.4.10) was strongly inhibited when ovophosphatidylcholine and saturated phosphatidylcholines with acyl chain lengths of more than eight carbon atoms were mixed with its substrate. In contrast, dihexanoylglycerophosphocholine produces a marked activation attended by a breakdown of the bilayer structure of the substrate. 2. C12, C14, and C16 lysophosphatidylcholines gave a progressive inhibition of the enzyme with increasing chain length; C10 lysophosphatidylcholine activated the reaction. 3. The enzyme was strongly inhibited by blood plasma and serum and by blood lipoproteins. 4. Phosphatidic acid, and certain lysophosphatidic acids (oleoyl and palmitoylglycerophosphates) activated the hydrolysis at a physiological pH, whereas decanoylglycerophosphate had little effect. 5. Phosphatidic acid at a concentration of 1% molar total lipid P produced an enhancement of the hydrolysis of the phosphatidylinositol substrate contained in a lipid environment which approximated to the inner (cytoplasmic) lamella of the plasma membrane bilayer of the liver sinusoidal cell surface. 6. The possible role of phospholipid molecules adjacent to phosphatidylinositol in controlling the hydrolysis of the latter in the proximity of a cell surface receptor is discussed. It is suggested that phosphatidic acid formed by the action of diacylglycerol kinase could amplify any increased hydrolysis of phosphatidylinositol which results from stimulation of the cell by an agonist.

Possible involvement of Ca2+-activated, phospholipid-dependent protein kinase in platelet activation.

Abstract: Ca2+-activated, phospholipid-dependent protein kinase recently found in rat brain (Takai, Y., Kishimoto, A., Iwasa, Y., Kawahara, Y., Mori, T., & Nishizuka, Y. (1979) J. Biol. Chem. 254, 3692-3695) is present in large quantities in human platelets. The activation of this enzyme appears to be initiated by unsaturated diacylglycerol and intimately related to phosphatidylinositol hydrolysis which is induced by thrombin. The enzyme is selectively and profoundly inhibited by several phospholipid-interacting compounds such as imipramine, verapamil, and tetracaine, which concomitantly inhibit aggregation and release reaction in parallel manners. It is suggestive that this protein kinase may be involved in the transmembrane control of intracellular events eventually leading to platelet activation.

Comparisons of monoacylglycerols and diacylglycerols of varying fatty acid composition as substrates for the acylglycerol kinase(s) of rat brain.

Abstract: The properties of diacylglycerol and monoacylglycerol kinase activities present in 90,000 x g pellet and 90,000 × g supernatant fractions from rat brain were examined and compared. Of the properties examined, time course (linear for 10 min), enzyme concentration, pH optimum (7.4–7.5), varying ATP (5 mM) and Mg2+ (10 mM) concentrations all showed similar optima for both activities. The optima for acylglycerol (5 mM for diacylglycerols; 3 mM for monoacylglycerols) and deoxycholate concentrations (0.1% for diacylglycerol kinase; 0.03% for monoacylglycerol kinase) differed slightly. Examination of the subcellular distribution for these activities also showed a similar pattern. All fractions showed significant activities, but the most was in the supernatant fraction. The similarities in properties and localization of the 2 kinase activities suggest a single enzyme may function. On this assumption, an extensive study using mono- and diacylglycerols of varying fatty acid composition gave the following results: (a) acylglycerols with the same fatty acid present showed increasing activity in the order: 1-monoacylglycerol, 2-monoacylglycerol and 1,2-diacylglycerols; (b) when saturated fatty acids were present the order of decreasing activity varied directly with increasing chain length for C10→C20; (c) when one or more unsaturated fatty acids were present good activities resulted, but no clear pattern emerged, although acylglycerols with18∶1 and18∶3 fatty acids were more active than those with18∶2 and20∶4 fatty acids. These patterns do not support a role for this kinase in producing phosphatidic acids or lyso phosphatidic acids of the correct composition to act as precursors for the de novo synthesis of the predominant 1-stearoyl, 2-arachidonoyl molecular species of phosphatidylinositol.

Partial purification of diphosphatidylglycerol synthetase from liver mitochondrial membranes

Abstract: The enzyme responsible for the conversion of phosphatidylglycerol to diphosphatidylglycerol (cardiolipin) in the presence of cytidine diphosphate diacylglycerol is firmly associated with mitochondr...

1,2-diacylglycerol kinase of human erythrocyte membranes. Assay with endogenously generated substrate.

Abstract: 1,2-Diacylglycerol kinase activity was measured in human erythrocyte membranes using an assay procedure in which the substrate was generated endogenously, either by treatment with a bacterial phospholipase C or by incubation with Ca24, which activates a membrane-bound polyphosphoinositide phosphodiesterase. The properties of 1,2-diacylglycerol kinase were broadly similar to those described previously, except that in the present work maximum activities were higher and there was evidence for a double pH optimum.

Docosahexaenoyl Chains are Introduced in Phosphatidic Acid During De Novo Synthesis in Retinal Microsomes

Abstract: Phosphatidic acid from microsomal membranes of bovine retina contains 21% of docosahexaenoate. If entire retinas are incubated during short-periods of time with dl-propranolol about a fourfold increase takes place in the content of microsomal phosphatidic acid. Moreover docosahexaenoate as well as other acyl chains are increased. It is suggested that a significative proportion of docosahexaenoyl groups of other phospholipids is introduced into the glycerolipids during the de novo biosynthesis of phospatidic acid in the endoplasmic reticulum. Diacylglycerol of the toad retina is highly enriched in docosahexaenoate and has been implicated to have a biosynthetic origin, Howeverm bovine retina diacylglycerols contain relatively low proportions of this fatty acid. This may indicate either that there is a mixture of several diacylglycerols with different fatty acid profiles or that the docosahexaenoate enriched phospatidic acid is metabolized without conversion into diacylglycerols. The alternative pathway investigated at present is docosahexaenoate containing phsophatidylserine synthesis from phosphatidic acid without involving base exchange reaction. When using 2-3H-glycerol as a marker of the de novo synthesis we obtained evidence of a rapid phosphatidic acid formation. A route introducing docosahexaenoate during phosphatidic acid synthesis may actively participate in controlling membrane function by changing membrane fluidity.

Interactions of chlorophyll a and terpenoid alcohols with chloroplast acyl lipids in monomolecular films

Abstract: Surface pressure-area measurements of purified chlorophyll a and monogalactosyl diacylglycerol in mixed monolayers were performed at 20°C with an automatic recording surface film balance at a constant compression rate. In addition structural parts of the chlorophyll and the monogalactosyl diacylglycerol as phytol and geranylgeraniol on one hand and different fatty acids on the other were studied pure and in mixed films. All components studied formed stable monomolecular films. Chlorophyll a and monogalactosyl diacylglycerol showed miscibility. Phytol was immiscible with synthetized monogalactosyl diacylglycerol containing only stearic acid. Mixed monolayers of phytol and monogalactosyl diacylglycerol isolated from barley containing 83 mol % a-linolenic acid showed a strong interaction. An increased miscibility and association were found between phytol and fatty acids with increasing unsaturation. The results are discussed as a model for the localization of part of chlorophyll a in the thylakoid membrane.

Phosphatidylinositol as a Source of Diacylglycerol to Promote Membrane Fusion in Exocytosis

Abstract: Twenty years ago an enzyme hydrolyzing phosphatidylinositol by the phospholipase C route was first reported (Kemp et al., 1959) and shown to be activated by calcium ions. The products of the reaction are diacylglycerol and inositol phosphate. Subsequent work has shown that the enzyme is widely distributed in mammalian tissues and that it is the key enzyme in what has been called the ‘phosphatidylinositol effect’ (Hokin & Hokin, 1953). This is the increased turnover of phosphatidylinositol, often measured by 32P incorporation, in response to activation of various types of plasma membrane receptors. For recent reviews, see Michell (1975) and Hawthorne and Pickard (1979). The physiological significance of the effect remains uncertain, though Michell and others believe that it is associated with calcium gating (Michell et al., 1977 Berridge & Fain, 1979). A conference volume presents other points of view (Wells & Eisenberg, 1978). Our purpose here is not to discuss why the effect is there. Instead we shall consider what part the phospholipase C might play, since it is reasonable to assume that phosphatidylinositol effect always begins with this enzyme.