Difference Between Sphingomyelin And Phosphatidylcholine By Chemical Test

FIGURE 10-24 Determination of the structure of a fatty acid by mass spectrometry. The fatty acid is first converted to a derivative that minimizes migration of the double bonds when the molecule is fragmented by electron bombardment. The derivative shown here is a picolinyl ester of linoleic acid—18:2(A9,12) (Mr 371)—in which the alcohol is picolinol (red). When bombarded with a stream of electrons, this molecule is volatilized and converted to a parent ion (M+; Mr 371), in which the N atom bears the positive charge, and a series of smaller fragments produced by breakage of C—C bonds in the fatty acid. The mass spectrometer separates these charged fragments according to their mass/charge ratio (m/z). (To review the principles of mass spectrometry, see Box 3-2.)

The prominent ions at m/z = 92, 108, 151, and 164 contain the pyridine ring of the picolinol and various fragments of the carboxyl group, showing that the compound is indeed a picolinyl ester. The molecular ion (m/z = 371) confirms the presence of a C-18 fatty acid with two double bonds. The uniform series of ions 14 atomic mass units (amu) apart represents loss of each successive methyl and methylene group from the right end of the molecule (C-18 of the fatty acid), until the ion at m/z = 300 is reached. This is followed by a gap of 26 amu for the carbons of the terminal double bond, at m/z = 274; a further gap of 14 amu for the C-11 methylene group, at m/z = 260, and so forth. By this means the entire structure is determined, although these data alone do not reveal the configuration (cis or trans) of the double bonds.

SUMMARY 10.4 Working with Lipids

■ In the determination of lipid composition, the lipids are first extracted from tissues with organic solvents and separated by thin-layer, gas-liquid, or high-performance liquid chromatography.

■ Phospholipases specific for one of the bonds in a phospholipid can be used to generate simpler compounds for subsequent analysis.

■ Individual lipids are identified by their chromatographic behavior, their susceptibility to hydrolysis by specific enzymes, or mass spectrometry.

Key Terms

Terms in bold are defined in the glossary.

fatty acid 343 triacylglycerol 345 lipases 346 phospholipid 348 glycolipid 348 glycerophospholipid 349

ether lipid 349

plasmalogen 349

galactolipid 351 sphingolipid 352

ceramide 352 sphingomyelin 352 glycosphingolipid 352 cerebroside 352

globoside 352

neutral glycolipids 352 gangliosides 352 sterols 354 cholesterol 355 prostaglandins 359 thromboxanes 359 leukotrienes 359 vitamin 360

vitamin D3 361 cholecalciferol 361 vitamin A (retinol) 361 vitamin E 362 tocopherols 362 vitamin K 363 dolichol 363

Chapter 10 Problems 367

General

Gurr, M.I. & Harwood, J.L. (1991) Lipid Biochemistry: An Introduction, 4th edn, Chapman & Hall, London.

A good general resource on lipid structure and metabolism, at the intermediate level.

Vance, D.E. & Vance, J.E. (eds) (2002) Biochemistry of Lipids, Lipoproteins, and Membranes, New Comprehensive Biochemistry, Vol. 36, Elsevier Science Publishing Co., Inc., New York.

An excellent collection of reviews on various aspects of lipid structure, biosynthesis, and function.

Structural Lipids in Membranes

Bogdanov, M. & Dowhan, W. (1999) Lipid-assisted protein folding. J. Biol. Chem. 274, 36,827-36,830.

A minireview of the role of membrane lipids in the folding of membrane proteins.

De Rosa, M. & Gambacorta, A. (1988) The lipids of archaebac-teria. Prog. Lipid Res. 27, 153-175.

Dowhan, W. (1997) Molecular basis for membrane phospholipid diversity: why are there so many lipids? Annu. Rev. Biochem. 66, 199-232.

Gravel, R.A., Kaback, M.M., Proia, R., Sandhoff, K., Suzuki, K., & Suzuki, K. (2001) The GM2 gangliosidoses. In The Metabolic and Molecular Bases of Inherited Disease, 8th edn (Scriver, C.R., Sly, W.S., Childs, B., Beaudet, A.L., Valle, D., Kinzler, K.W., & Vogelstein, B., eds), pp. 3827-3876, McGraw-Hill, Inc., New York. This article is one of many in a four-volume set that contains definitive descriptions of the clinical, biochemical, and genetic aspects of hundreds of human metabolic diseases—an authoritative source and fascinating reading.

Hoekstra, D. (ed.) (1994) Cell Lipids, Current Topics in Membranes, Vol. 4, Academic Press, Inc., San Diego.

Lipids as Signals, Cofactors, and Pigments

Bell, R.M., Exton, J.H., & Prescott, S.M. (eds) (1996) Lipid Second Messengers, Handbook of Lipid Research, Vol. 8, Plenum Press, New York.

Binkley, N.C. & Suttie, J.W. (1995) Vitamin K nutrition and osteoporosis. J. Nutr. 125, 1812-1821.

Brigelius-Flohe, R. & Traber, M.G. (1999) Vitamin E: function and metabolism. FASEB J. 13, 1145-1155.

Chojnacki, T. & Dallner, G. (1988) The biological role of dolichol. Biochem. J. 251, 1-9.

Clouse, S.D. (2002) Brassinosteroid signal transduction: clarifying the pathway from ligand perception to gene expression. Mol. Cell 10, 973-982.

Lemmon, M.A. & Ferguson, K.M. (2000) Signal-dependent membrane targeting by pleckstrin homology (PH) domains. Biochem. J. 350, 1-18.

Prescott, S.M., Zimmerman, G.A., Stafforini, D.M., & McIntyre, T.M. (2000) Platelet-activating factor and related lipid mediators. Annu. Rev. Biochem. 69, 419-445.

Schneiter, R. (1999) Brave little yeast, please guide us to Thebes: sphingolipid function in S. cerevisiae. BioEssays 21, 1004-1010.

Suttie, J.W. (1993) Synthesis of vitamin K-dependent proteins. FASEB J. 7, 445-452.

Vermeer, C. (1990) y-Carboxyglutamate-containing proteins and the vitamin K-dependent carboxylase. Biochem. J. 266, 625-636. Describes the biochemical basis for the requirement of vitamin K in blood clotting and the importance of carboxylation in the synthesis of the blood-clotting protein thrombin.

Viitala, J. & Jarnefelt, J. (1985) The red cell surface revisited. Trends Biochem. Sci. 10, 392-395.

Includes discussion of the human A, B, and O blood type determinants.

Weber, H. (2002) Fatty acid-derived signals in plants. Trends Plant Sci. 7, 217-224.

Zittermann, A. (2001) Effects of vitamin K on calcium and bone metabolism. Curr. Opin. Clin. Nutr Metab. Care 4, 483-487.

Working with Lipids

Christie, W.W. (1998) Gas chromatography-mass spectrometry methods for structural analysis of fatty acids. Lipids 33, 343-353. A detailed description of the methods used to obtain data such as those presented in Figure 10-24.

Christie, W.W. (2003) Lipid Analysis, 3rd edn, The Oily Press, Bridgwater, England.

Hamilton, R.J. & Hamilton, S. (eds) (1992) Lipid Analysis: A Practical Approach, IRL Press at Oxford University Press, New York.

This text, though out of print, is available as part of the IRL Press Practical Approach Series on CD-ROM, from Oxford University Press (www.oup-usa/acadsci/pasbooks.html).

Matsubara, T. & Hagashi, A. (1991) FAB/mass spectrometry of lipids. Prog. Lipid Res. 30, 301-322.

An advanced discussion of the identification of lipids by fast atom bombardment (FAB) mass spectrometry, a powerful technique for structure determination.

Problems

1. Operational Definition of Lipids How is the definition of "lipid" different from the types of definitions used for other biomolecules that we have considered, such as amino acids, nucleic acids, and proteins?

2. Melting Points of Lipids The melting points of a series of 18-carbon fatty acids are: stearic acid, 69.6 °C; oleic acid, 13.4 °C; linoleic acid, —5 °C; and linolenic acid, —11 °C. (a) What structural aspect of these 18-carbon fatty acids can be correlated with the melting point? Provide a molecular explanation for the trend in melting points.

(b) Draw all the possible triacylglycerols that can be constructed from glycerol, palmitic acid, and oleic acid. Rank them in order of increasing melting point.

(c) Branched-chain fatty acids are found in some bacterial membrane lipids. Would their presence increase or decrease the fluidity of the membranes (that is, give them a lower or higher melting point)? Why?

3. Preparation of Béarnaise Sauce During the preparation of béarnaise sauce, egg yolks are incorporated into melted butter to stabilize the sauce and avoid separation. The stabilizing agent in the egg yolks is lecithin (phosphatidylcholine). Suggest why this works.

4. Hydrophobic and Hydrophilic Components of Membrane Lipids A common structural feature of membrane lipids is their amphipathic nature. For example, in phosphatidylcholine, the two fatty acid chains are hydrophobic and the phosphocholine head group is hydrophilic. For each of the following membrane lipids, name the components that serve as the hydrophobic and hydrophilic units: (a) phosphatidyl thanolamine; (b) sphingomyelin; (c) galactosyl-cerebroside; (d) ganglioside; (e) cholesterol.

5. Alkali Lability of Triacylglycerols A common procedure for cleaning the grease trap in a sink is to add a product that contains sodium hydroxide. Explain why this works.

T6. The Action of Phospholipases The venom of the Eastern diamondback rattler and the Indian cobra contains phospholipase A2, which catalyzes the hydrolysis of fatty acids at the C-2 position of glycerophospholipids. The phospholipid breakdown product of this reaction is lysolecithin (lecithin is phosphatidylcholine). At high concentrations, this and other lysophospholipids act as detergents, dissolving the membranes of erythrocytes and lysing the cells. Extensive hemolysis may be life-threatening.

(a) Detergents are amphipathic. What are the hy-drophilic and hydrophobic portions of lysolecithin?

(b) The pain and inflammation caused by a snake bite can be treated with certain steroids. What is the basis of this treatment?

(c) Though high levels of phospholipase A2 can be deadly, this enzyme is necessary for a variety of normal metabolic processes. What are these processes?

7. Intracellular Messengers from Phosphatidylinosi-tols When the hormone vasopressin stimulates cleavage of phosphatidylinositol 4,5-bisphosphate by hormone-sensitive phospholipase C, two products are formed. What are they? Compare their properties and their solubilities in water, and predict whether either would diffuse readily through the cytosol.

8. Storage of Fat-Soluble Vitamins In contrast to water-soluble vitamins, which must be a part of our daily diet, fat-soluble vitamins can be stored in the body in amounts sufficient for many months. Suggest an explanation for this difference, based on solubilities.

9. Hydrolysis of Lipids Name the products of mild hydrolysis with dilute NaOH of (a) 1-stearoyl-2,3-dipalmitoyl-glycerol; (b) l-palmitoyl-2-oleoylphosphatidylcholine.

10. Effect of Polarity on Solubility Rank the following in order of increasing solubility in water: a triacylglycerol, a diacylglycerol, and a monoacylglycerol, all containing only palmitic acid.

11. Chromatographic Separation of Lipids A mixture of lipids is applied to a silica gel column, and the column is then washed with increasingly polar solvents. The mixture consists of phosphatidylserine, phosphatidylethanolamine, phosphatidylcholine, cholesteryl palmitate (a sterol ester), sphingomyelin, palmitate, «-tetradecanol, triacylglycerol, and cholesterol. In what order do you expect the lipids to elute from the column? Explain your reasoning.

12. Identification of Unknown Lipids Johann Thu-dichum, who practiced medicine in London about 100 years ago, also dabbled in lipid chemistry in his spare time. He isolated a variety of lipids from neural tissue, and characterized and named many of them. His carefully sealed and labeled vials of isolated lipids were rediscovered many years later.

(a) How would you confirm, using techniques not available to Thudichum, that the vials labeled "sphingomyelin" and "cerebroside" actually contain these compounds?

(b) How would you distinguish sphingomyelin from phosphatidylcholine by chemical, physical, or enzymatic tests?

13. Ninhydrin to Detect Lipids on TLC Plates Ninhy-drin reacts specifically with primary amines to form a purplish-blue product. A thin-layer chromatogram of rat liver phospholipids is sprayed with ninhydrin, and the color is allowed to develop. Which phospholipids can be detected in this way?

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Responses

  • Prudenzia Napolitani
    How would you distinguish sphingomyelin from phosphatidylcholine by chemical test?
    2 years ago
  • jeremy
    How can we distinguish sphingonyelin from phosphatidylcholine by chemical or an enzymatic test?
    2 years ago
  • Jonne Tuimala
    How can we distinguish sphingomyelin from phosphatidylcholine by chemical or an enzymatic test?
    2 years ago
  • LORI
    How to distimguish the physical test of sphingomyelin and phosphatidylcholine?
    2 years ago
  • jan anderson
    How would you distinguish sphingomyelin from phospha tidylcholine by physical?
    2 years ago
  • Melissa
    How would u distinguish sphingomyelin from phosphatidylcholine through physical test?
    2 years ago
  • robinia
    How would you distinguish from phosphatidyl choline using chemical test?
    2 years ago
  • Nerea
    How would you differentiate between sphingomyelin from phosphatidyl choline by enzymatic test?
    2 years ago
  • ayla
    What are difference between sphingomyelin and phosphatidylcholine?
    2 years ago
  • gerontius
    What are the possible structures of triaglycerol that could be construct from glycerol, plamitic?
    2 years ago
  • Teodros
    What is the difference between sphingomyelin from phosphatidylcholine by chemical test?
    2 years ago
  • fiori
    How to distiguish sphingomyelin from phosphatidyl by chemical process?
    2 years ago
  • nora
    How to distinquish sphingomyelin from phosphatidylcholine by chemical test?
    2 years ago
  • kristian
    How to distinquish sphingomyelin from phosphatidylcholine by physical test?
    2 years ago
  • azzeza
    How will you distinguish sphinogomyelin from phosphatidyl choline by chemical?
    2 years ago
  • senja
    How would yhu distinguish sphingomyelin from phosphatidtylcholine by chemical test?
    2 years ago
  • ERMIAS
    How would yo distinguish sphinogomyelin from phosphatidyl choline by chemical process?
    2 years ago
  • anu ukkonen
    What are the chemical difference between sphingomyelin and phosphotidycholine?
    2 years ago
  • frank
    How do u distinguish sphingomyelin from phosphatdylcholine by chemical test?
    2 years ago
  • andreas keller
    How would you describe sphingomyelin from phosphatidylcholine by chemical test?
    2 years ago
  • AARNE
    How would u distinguish sphingomyelin from phosphatidylcholine by chemical physical or enzymic test?
    2 years ago
  • mohamed
    How would you distinguish sphingomyelin from phosphadylcholine by chemical test?
    2 years ago
  • Teija
    How would you distinguish sphingomyelin from phosphatidyl choline by chemical, physical or enzymatic?
    2 years ago
  • KIBRA
    How would you distinguish sphingomyelin from phosphatdylcholin by chemical, physical,enzymatic test?
    2 years ago
  • THORSTEN
    How would you dinstoguish sphimhomyelin from phosphatylcholine?
    2 years ago
  • Basso
    Why lecithin phosphatidycholine is used as a stabilising agent betwwen egg nd butter?
    2 years ago

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