Phospholipid Metabolism

McMurray, W. C.; Magee, W L

doi:10.1146/annurev.bi.41.070172.001021

Cited by 197 publications

(59 citation statements)

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“…Whereas PtdEtn and PtdSer account for about 18.5% and 9.0%, respectively, of rat liver plasma membrane phospholipids [20], glycosyl-PtdIns accounts for only about 0.5% [4]. The purification procedure described under Materials and Methods was designed to purify amidinated glycosyl-PtdIns free from other amidinated lipid species.…”

Section: Identification Of Chemically Labelled Glycosyl-ptdinsmentioning

confidence: 99%

Asymmetric distribution of the phosphatidylinositol‐linked phospho‐oligosaccharide that mimics insulin action in the plasma membrane

Varela

Alvarez

Clemente

et al. 1990

European Journal of Biochemistry

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We have investigated the topography of a glycosyl-phosphatidylinositol implicated in insulin action by a combination of two complementary methods : (a) chemical labelling with a non-permeable (isethionyl acetimidate) and a permeable (ethyl acetimidate) probe; and (b) enzymatic modifications with P-galactosidase (EC 3.2.1.23) or phosphatidylinositol-specific phospholipase C (EC 3.1.4.3). Using the first approach the majority of the glycosyl-phosphatidylinositol is found in the outer surface of intact hepatocytes, adipocytes, fibroblasts and lymphocytes, but not in erythrocytes which presented only a 20% of the total labelled glycosyl-phosphatidylinositol to the exterior. Upon insulin addition ( 3 0 nM), about 60% of the total glycosyl-phosphatidylinositol was hydrolysed in both hepatocytes and adipocytes but not in erythrocytes. In agreement with the extracellular localization in hepatocytes and with the proposed role of this glycolipid in insulin action, treatment of rat hepatocytes with fl-galactosidase from Escherichia coli, an enzyme that hydrolyses the oligosaccharide moiety of the glycosylphosphatidylinositol, cleaved 65% of the total glycophospholipid and blocked the effect of insulin (but not of glucagon) on pyruvate kinase (EC 2.7.1.40). Similar treatment with phosphatidylinositol-specific phospholipase C from Bacillus cereus hydrolysed 62% of the total glycosyl-phosphatidylinositol. From the various approaches used it is concluded that the majority of this glycophospholipid is at the outer surface in a variety of insulinsensitive cells. In a variety of cells including murine myocytes BC3H1 [l], H35 hepatoma cells [2], T lymphocytes [3] and rat hepatocytes[4], insulin promotes the phosphodiesteratic hydrolysis of a glycosyl-phosphatidylinositol (glycosyl-PtdIns) and thus releases and increases the intracellular levels of the polar headgroup of this lipid. This polar headgroup, a phosphooligosaccharide containing inositol, glucosamine, galactose and phosphate [I, 2, 5, 61, mimics insulin-directed effects on protein phosphorylation/dephosphorylation [7], as well as a variety of the biological effects of this hormone, including lipolysis [8], lipogenesis [9] and the effects of the hormone on pyruvate kinase, glycogen phosphorylase and cyclic AMP levels [lo]. These studies suggest that this glycosyl-Ptdlns is implicated in insulin action. This glycosyl-PtdIns has features in common with the glycosyl-PtdIns anchor of a number of cell membrane proteins (for recent reviews see [I 1 -131). These similarities include : (a) the observation that the insulin-sensitive glycosyl-PtdIns is hydrolysed by the phosphatidyl-inositol-specific phospholipase C (PtdIns-specific phospholiCorrespondence to I. Varela, Metabolismo, Nutricion y Hormonas, Fundacion Jimenez Diaz and C.S.I.C

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Section: Identification Of Chemically Labelled Glycosyl-ptdinsmentioning

confidence: 99%

Asymmetric distribution of the phosphatidylinositol‐linked phospho‐oligosaccharide that mimics insulin action in the plasma membrane

Varela

Alvarez

Clemente

et al. 1990

European Journal of Biochemistry

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“…CDP-diacylglycerol is a central intermediate in the synthesis of phospholipids, serving as a precursor for phosphatidylglycerol (and thereby cardiolipin), phosphatidylinositol and, in some organisms, phosphatidylserine (6)(7)(8)10,12,15). It is a branchpoint product which exists at very low concentrations within the membranes (7,8,10,12,15).…”

mentioning

confidence: 99%

“…It is a branchpoint product which exists at very low concentrations within the membranes (7,8,10,12,15). The enzyme involved in this synthesis may, therefore, play a role in regulation ofphospholipid levels, and an understanding of the characteristics of the enzyme is critical toward understanding its role in phospholipid synthesis.…”

mentioning

confidence: 99%

Biosynthesis of Cytidine 5′-Diphosphate-diacylglycerol in Endoplasmic Reticulum and Mitochondria of Castor Bean Endosperm

Kleppinger-Sparace¹,

Moore²

1985

Plant Physiol.

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Cytidine 5'-triphosphate (CTP):phosphatidate cytidyltransferase from the endoplasmic reticulum and mitochondria of Ricinus communis L. var Hale was characterized. The endoplasmic reticulum enzyme has a pH optimum of 6.5 and a divalent cation is required, Mn2" being preferred and giving maximum activity at 2.5 millimolar. The estimated K,. for CTP is 16.7 micromolar, but that for phosphatidate could not be determined accurately. The activity was inhibited by both deoxycholate and Triton X-100 at concentrations as low as 0.01% (w/w).The mitochondrial enzyme has a pH optimum of 6.0 and a divalent cation requirement similar to that of the endoplasmic reticulum. Maximum stimulation of the reaction by substrates occurred with 1.5 miUimolar phosphatidate (from egg phosphatidylcholine) and about 400 micromolar CTP. The apparent K,. for phosphatidate could not be estimated accurately since activity was obtained in the absence of added lipid, apparently utilizing endogenous substrate. The K,. estimated for C1TP was altered by the presence of the detergent Triton X-100; in its absence the value was 33.3 micromolar, but in its presence the value was 66.7 micromolar. Inclusion of 0.6% (w/w) Triton X-100 in the assay mixture stimulated the activity about 2.5-fold.

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“…However, substantial evidence has accumulated regarding the ability of intact mitochondria to synthesize at least a portion of the total phospholipids constituting their membranes. Animal mitochondrial phospholipid synthesis has been studied extensively and is well reviewed (15,20,29,41), but plant mitochondria have received comparatively less attention (18,28). In spite of this, it has been suggested that plant mitochondria have the capacity to synthesize many of their membrane lipids.…”

mentioning

confidence: 99%