The Integration And Control Of Animal Acylglycerol Metabolism
The major function of TAG in animals is as a source of fatty acids to be used as metabolic fuel. A full description of the overall fuel economy of the body requires an understanding of the metabolism storage, transport, synthesis, oxidation of the fatty acids as well as of the integration of fat and carbohydrate metabolism. interconversion of different types of fuels is hormonally regulated to maintain blood glucose concentration within the normal range and ensure storage of excess dietary...
Some plants use lipids as a fuel stored as minute globules in the seed
There are many hundred varieties of plants known to have oil-bearing seeds, but only a few are significant commercially. These are listed in Table 3.2 with their fatty acid compositions. Most are important sources of edible oils for human foods or animal feeds, but some are used for other industrial purposes such as paints, varnishes and lubricants. Although the seed is the most important organ for the storage of triacylglycerols, some species store large quantities of oil in the mesocarp or...
Prostaglandins and other eicosanoids are rapidly catabolized
We have already mentioned that thromboxane A2 and prostacyclin have very short half-lives in vivo. In addition, it was shown by Vane and Piper in the late 1960s that prostaglandins like PGE2 or PGF2a were rapidly catabolized and did not survive a Fig. 2.43 Interaction of thromboxanes and prostacyclins in regulating platelet cAMP levels. Fig. 2.43 Interaction of thromboxanes and prostacyclins in regulating platelet cAMP levels. single pass through the circulation. The lung plays a major role in...
material for terpenoid as well as fatty acid synthesis
The biosynthesis of cholesterol is well covered in standard biochemistry textbooks and only the more important features will be outlined here. However, it should be added that a great deal of work has gone into solving the pathway of cholesterol formation with those concerned receiving no less than 13 Nobel prizes between them The precursor pool in mammalian cells is the cytosolic acetyl-CoA. This acetyl-CoA may be derived, for example, from 3-oxidation of fatty acids by mitochondria or...
Ii
10-methytene stearate 10-methy stearate Fig. 2.14 Production of tuberculostearic acid in Mycobacterium phlei. chain. However, mid-chain hydroxylations are also found - a good example being the formation of ricinoleic acid D-12-hydroxyoleic acid Table 2.4 . This acid accounts for about 90 of the triacylgly-cerol fatty acids of castor oil and about 40 of those of ergot oil, the lipid produced by the parasitic fungus, Claviceps purpurea. In developing castor seed, ricinoleic acid is synthesized by...
Diseases Involving Changes Or Defects In Lipid Metabolism
Defects in a variety of lipid metabolic pathways can give rise to inappropriately high or sometimes low concentrations of lipoproteins in the blood. This in turn may Fig. 5.16 The acylation stimulating protein ASP system in adipose tissue. Arrival of a chylomicron particle in the capillary sends a signal to the adipocyte probably by transfer of a protein carried by the chylomicron to a specific receptor on the adipocyte surface , which increases secretion of the three proteins D, B and C3,...
Lipids and Membrane Structure
Carruthers, A. amp Melchior, D.L. 1986 How bilayer lipids affect membrane protein activity. Trends in Biochemical Sciences, 11, 331-335. Dai, J. amp Sheetz, M.P. 1998 Cell membrane mechanics. Methods in Cell Biology, 55, 157-171. de Kruiff, B., et al. 1984 Lipid polymorphism and membrane function. In Enzymes of Biological Membranes ed. A. Martinosi , pp. 131-204. Plenum Press, New York. Edidin, M. 1997 Lipid microdomains in cell surface membranes. Current Opinion in Structural Biology, 7,...
Mycobacteria contain specialized cellwall lipids
The mycobacterial cell wall contains three components. First, there is a skeleton consisting of arabi-nogalactan mycolate covalently linked through a phosphodiester bond to peptidoglycan. In addition, peptides that can be removed by proteolysis and free lipids are important components. The skeleton is a branched polymer of D-arabi-nose and D-galactose in a 5 2 ratio. Every tenth arabinose has a mycolic acid esterified to the 5-hydroxyl. These mycolic acids are 60C-90C fatty acids that are...
Lipopolysaccharide forms a major part of the cell envelope of Gramnegative
In Gram-negative bacteria, the wall is far more complex than for Gram positives and contains glycopeptide, lipopolysaccharide, phospholipid and protein. Also, there is not such a clear distinction between the wall and the membrane as in Gram positives. Up to 20 of the wall contents may be lipids, but only a proportion of these are readily extractable by conventional solvent methods. This is because of the covalent nature of the lipopoly-saccharide linkages. The cytosol of Gram-negative bacteria...
A novel cofactor for phospholipid synthesis was found by accident
After the problem of phosphatidic acid biosynthesis had been solved, interest then grew in the pathways to more complex lipids. What was the origin of the group 'X' attached to the phosphate The first significant finding in connection with phosphati-dylcholine biosynthesis was made when Kornberg and Pricer demonstrated that the molecule phos-phorylcholine was incorporated intact into the lipid. This they did by incubating phosphorylcho- line, labelled both with 32P and 14C in a known...
Triacylglycerols In Animals And Plants
Both animals and plants can store TAG in specialized tissues as long-term fuel reserves. 3.3.1 Adipose tissue depots are the sites of TAG storage in animals As discussed in more detail in Section 4.2.1, TAG provide a concentrated form of metabolic energy, having a metabolizable energy value of 38kjg_1. When the energy supply from the diet exceeds the energy demands of the body, TAG molecules are deposited in adipose tissue. They have the advantage that they can be stored in anhydrous form and...
Essential Fatty Acids And The Biosynthesis Of Eicosanoids
Some types of polyunsaturated fatty acids, the so-called essential fatty acids, are converted into oxygenated fatty acids with potent physiological effects. These include effects on muscle contraction, cell adhesion, immune function and vascular tone. In Section 2.2.5 we described the biosynthesis of the polyunsaturated fatty acids and indicated that mammals lack the A12 and A15-desaturases. They cannot, therefore, synthesize linoleic or a-linolenic acids. It turns out, however, that these...
Structural Chemistry And Nomenclature
Naming systems are complex and have to be learned. The naming of lipids often poses problems. When the subject was in its infancy, research workers gave names to substances that they had newly discovered. Often, these substances would turn out to be impure mixtures and as the chemical structures of individual lipids became established, rather more systematic naming systems came into being. Later, these were further formalized under naming conventions laid down by the International Union of Pure...
Lipids and proteins interact to determine membrane structure and shape
Dowhan, W. 1997 Molecular basis for membrane phospholipid diversity why are there so many lipids Annual Review of Biochemistry, 66, 199-232. Eisenberg, D. 1984 Three-dimensional structure of membrane and surface proteins. Annual Review of Biochemistry, 53, 595-623. Israelachvili, J.N. 1978 The packing of lipids and proteins in membranes. In Light Transducing Membranes Structure, Function and Evolution ed. D.W. Deamer , pp. 91-107. Academic Press, New York. op den Kamp, J.A.F., Roelofsen, B. amp...
Paps
CMP-NeuAc CMP-N-acetyl neuraminic acid PAPS cytidine derivatives used in phospholipid biosynthesis. The gangliosides are made by transfer of the neuraminic acid residue to the growing sugar chain at various stages and four series of gangliosides result from these reactions Fig. 7.15 . The picture of ganglioside synthesis was built up largely by the work of Roseman, Brady and their colleagues in the USA. The way in which they worked out the sequence of sugar additions was by testing the...
membranes reveals their fluid properties
Fluidity in membranes is an easily visualized phenomenon and is a term that is widely used. However, it can be misleading. For example, it is commonly assumed and stated that making membrane lipids more saturated or adding cholesterol makes a membrane less fluid. The assumption is that such alteration will reduce the speed of movement of lipids. However, introduction of cholesterol into phosphatidylcholine model membranes has no effect on lateral movement and may actually increase rotational...
Degradation Of Fatty Acids
The main pathways of fatty acid breakdown involve oxidation at various points on the acyl chain or lipox-idation at certain double bonds of specific unsaturated fatty acids. The main forms of fatty acid oxidation are termed a, p and m. They are named depending on which carbon on the acyl chain is attacked Of the oxidations, P-oxidation is the most general and prevalent. 2.3.1 p-Oxidation is the most common type of biological oxidation of fatty acids Long-chain fatty acids, combined as...
Info Ebh
b Castor oil contains 90 of ricinoleic acid see Table 2.4 . c Evening primrose oil contains about 10 of y-linolenic acid see Table 2.3 . b Castor oil contains 90 of ricinoleic acid see Table 2.4 . c Evening primrose oil contains about 10 of y-linolenic acid see Table 2.3 . The vegetable oils are listed according to whether their main commercial use is in A foods, B chemicals. Some crops mainly used in foods also contribute to the chemical industry e.g. use of palm oil in making 'biodiesel', a...
Sterols
Sterols are common in the membranes of eukaryotic organisms, where they are important in providing stability, but are rare in prokaryotes. In the membranes of higher animals cholesterol is the almost exclusive sterol constituent whereas in plants, other sterols, such as fi-sitosterol, predominate. Cholesterol and the functionally related sterols of fungi and plants are significant components of many organisms, especially of their external cellular membranes. However, they are not needed by all...
Membrane lipids are modified to maintain fluidity at low temperatures
We have already seen that membrane lipids can exist in the gel - or liquid - crystalline phases, depending on the prevailing temperature. Whereas isolated lipid samples show a sharp gel-liquid phase transition, naturally occurring lipids show broad non-cooperative transitions due to the heterogeneity of the acyl chains. For a series of molecular species of, say, phosphatidylcholine, the temperature Tc for the gel-liquid phase transition depends on the fatty acid composition with cis-unsaturated...
Pulmonary Surfactant
A unique lipoprofein, comprising almosf entirely dipal-mifoylphosphafidylcholine as ifs lipid componenf, acfs as a lung surfacfanf. Ifs function is fo lower alveolar surface fension and prevenf lung collapse. Every time we breathe out, our lungs are prevented from collapsing by a unique lipoprotein mixture termed the 'pulmonary surfactant'. Pulmonary surfactant is adsorbed at the alveolar airliquid interface where it lowers the surface tension and, therefore, reduces the contractile force at...
Transbilayer lipid asymmetry is an essential feature of all known biological
The first natural membrane to be examined for asymmetry was that from erythrocytes. Such cells are very convenient for membrane studies since erythrocytes can be easily purified in large quantities and contain only a single membrane. In order to study the two leaflets of such membranes, intact cells were probed or labelled in order to establish those components that were in the outer leaflet i.e. that were accessible . In a second experiment, the erythrocytes were broken by a suitable method...
phosphoglycerides can be made using CDPbases
As can be seen in Fig. 7.1, diacylglycerol generated by phosphatidate phosphohydrolase can have several fates, one of which is to be used for generation of the zwitterionic phosphoglycerides, phosphatidylcholine and phosphatidylethanola-mine. In animals and plants the CDP-base pathway is the main pathway for production of phosphati-dylcholine, which represents 40-50 of the total lipids in most of their membranes. Three enzymic steps are used Fig. 7.2 . First, the base either choline or...
phosphoglyceride synthesis in different organisms
A major difference between phosphoglyceride formation in yeasts and bacteria compared to animals is in the production of phosphatidylserine. In the simpler organisms, phosphatidylserine plays a major role as an intermediate in the production of phosphatidylethanolamine and phosphatidylcho-line and is made from CDP-diacylglycerol Figs 7.4 and 7.5 . However, in animals it is made via an exchange reaction in which the head group of an existing phospholipid usually phosphatidyletha-nolamine or...
Lipid Storage Diseases Lipidoses
If tissues lack a key breakdown enzyme, lipids accumulate. The resulting pathologies are usually fatal. However, enzyme replacement therapies can be effective. Several inborn errors of metabolism exist in which the missing enzyme is one that is involved in the breakdown of a specific lipid molecule. Since the biosynthesis of these lipids is not impaired, the result of the enzyme deficiency is the gradual accumulation of lipids in the tissues. Most of the important diseases of this type are ones...
Phospholipase D In Cell Signalling
After years of uncertainty about a role for phospholipase D, it was discovered that the enzyme can generate a wide range of compounds involved, inter alia, in vesicular trafficking, secretion, tumour promotion, membrane deterioration and senescence and as plant hormones. Phospholipase D was first discovered in plants some 50 years ago. The enzyme is widespread and often very active in such organisms but is also present in mammals, fungi and bacteria. For a long time the presence of an active...
Dag
Fig. 7.1 The basic Kennedy pathway for glycerolipid biosynthesis in animals and plants. acyl specificities. Thus, in animals and for the extra-chloroplastic endoplasmic reticulum acyl-transferases in plants, saturated fatty acids e.g. palmitate are preferred for esterification at position 1, whereas unsaturated fatty acids e.g. oleate are attached to the 2-hydroxyl. In chloroplasts, by contrast, the acyltransferases that utilize acyl-ACP typically place a saturated or unsaturated acid at...
The Phosphatidylinositol Cycle In Cell Signalling
The discovery of this cycle indicated that inositol phospholipids were important in hormone action. As far back as 1953, the husband and wife team, the Hokins, observed that stimulation of pancreatic secretion with acetylcholine led to a markedly increased incorporation of 32P into phospholipids. Further investigation showed that much of this incorporation was localized in phosphatidylinosi-tol. This led to the concept that the head group of phosphatidylinositol could be released through...
galactosylglycerides takes place in chloroplast envelopes
Since the galactosylglycerides are confined almost exclusively to chloroplasts, it would seem natural to seek an active enzyme preparation from these organelles. First, it was shown that carefully prepared isolated chloroplasts could incorporate 14C-galactose into the lipids. The nature of the substrates involved was not clear until Ongun and Mudd in California showed that an acetone powder of spinach chloroplasts would catalyse the incorporation of galactose from UDP-galactose into...
Lipids and membrane fusion
Membrane fusion is a very common process in cells. In eukaryotic organisms, many different fusion events can occur at any given time, participating in such diverse functions as secretion, endocytosis, intracellular digestion in lysosomes, cell division and the adjustment of mitochondrial numbers to a cell's energy requirements. Just a short consideration of the overall events of fusion will make it obvious that, during the process, the normal lipid bilayer structure must disappear. First of...
Cholesterol biosynthesis 1
Britton, G., Liaaen-Jensen, S. amp Pfander, H., eds. 1998 Carotenoids, Vol. 3, Biosynthesis and Metabolism. Bir-khauser, Basel. Discusses the early steps of isoprene metabolism including the non-mevalonate pathway , which are common to sterol formation. Brown, M.S. amp Goldstein, J.L. 1986 A receptor-mediated pathway for cholesterol homeostasis. Science, 232, 34-47. Mercer, E.I. 1993 Inhibitors of sterol biosynthesis and their applications. Progress in Lipid Research, 32,357-416. Ridgway, N.D.,...
Further Reading Gts
British Nutrition Foundation Task Force 1992 Report on Unsaturated Fatty Acids Nutritional and Physiological Significance. Chapman amp Hall, London. Calder, P.C., et al. 1998 Symposium of The Nutrition Society comprising twelve reviews on 'Lipids and the Immune System'. Proceedings of the Nutrition Society, 57, 487-585. Chow, C.K., ed. 1992 Fatty Acids in Foods and Their Health Implications. Marcel Dekker, New York. Forsyth, J.S. 1998 Lipids and infant formulas. Nutrition Research Reviews, 11,...
Aroma Compound In Food Ppt
warfarin, inhibit the y-carboxylation reaction, so preventing clotting. It was only in 1975 that it was discovered that bone tissue contains a y-carboxyglutamyl protein, osteocalcin, which accounts for up to 15 of non-collagenous proteins in bone. Fully carboxylated osteocalcin is able to form a strong complex with hydroxyapatite, the calcium phosphate mineral component of bone. Much circumstantial evidence suggests a key role for vitamin K in bone health. For example, treatment of pregnant...
Glycerolipids 1
Ansell, G.B. amp Hawthorne, J.N., eds. 1982 Phospholipids. Elsevier, Amsterdam. Cevc, G., ed. 1993 Phospholipids Handbook. Marcel Dekker, Basel. Dembitsky, V.M. 1996 Betaine ether-linked glycerolipids chemistry and biology. Progress in Lipid Research, 35, 1-52. Kates, M., ed. 1990 Glycolipids, Phosphoglycolipids and Sulphoglycolipids. Plenum Press, New York. Kaya, K. 1992 Chemistry and biochemistry of taurolipids. Progress in Lipid Research, 31, 87-108. See also specific chapters in multiauthor...
Chromatographic Techniques For Separating Lipids
The principles of chromatography are based on distribution between two phases, one moving, the other stationary. 1.7.1 The two phases can be arranged in a variety of ways A chromatogram so-named by its Polish inventor, Tswett, because he used the technique to separate plant pigments consists of two immiscible phases. One phase is kept stationary by either being held on an inert microporous support or being itself a microporous or particulate adsorbent solid the other phase is percolated...
Digestion and utilization of wax esters is poorly understood
The wax esters of fish and of jojoba seed oils are poorly hydrolysed by the pancreatic lipases of the human digestive system so that these lipids have poor nutritive value for man. Fish, such as salmon and herring grow rapidly when feeding on zooplankton rich in wax esters, yet do not contain these lipids themselves. Their digestive systems are adapted to the efficient hydrolysis of wax esters, most of the products being absorbed and resyn-thesized into TAG. Tissue breakdown of wax esters so...
Nadp
of palmitoyl-CoA with serine using a pyridoxal phosphate-requiring enzyme. The selectivity of the serine palmitoyltransferase accounts for the prevalence of 18C bases in most sphingolipids. Some very potent inhibitors of the reaction have been recently developed including a myriocin that is at least ten times better as an immunosuppressant than cyclosporin A. 3-Ketosphinganine is then reduced to sphinga-nine using NADPH. The desaturation of the hydrocarbon chain of sphinganine to yield...
Acp
Fig. 2.11 Arrangement of the partial reactions of one monomer of the animal fatty acid synthase. Information taken from Smith 1994 . The key active-site residues for each domain are indicated. condensing enzyme on the other half of the dimer Fig. 2.12 . Other experimental evidence demonstrated that translocation of acetyl and malonyl moieties from CoA esters to the 4'-phospho-pantetheine of the ACP domain also needs the dimeric form of the enzyme. However, Smith and colleagues have produced a...
Catabolism of glycosylglycerides
Enzymes are present in higher plant tissues that rapidly degrade glycosylglycerides. The initial attack is by an acyl hydrolase Section 7.2.5 , which removes acyl groups from both positions and has very high activity in some tissues such as runner bean leaves or potato tubers. Indeed, homogeniza-tion of the latter at a suitable pH in aqueous media results in the complete breakdown of all membrane lipids within a minute The activity of acyl hydro-lases and other lipid degradative enzymes in many...
Phosphoglyceride synthesis
Carman, G.M. amp Henry, S.A. 1999 Phospholipid biosynthesis in the yeast Saccharomyces cerevisiae and interrelationship with other metabolic processes. Progress in Lipid Research, 38, 361-399. Chao, W. amp Olson, M.S. 1993 Platelet activating factor receptors and signal transduction. Biochemical journal, 292, 617-629. Dircks, L. amp Sul, H.S. 1999 Acyltransferases of de novo glycerophospholipid biosynthesis. Progress in Lipid Research, 38, 461-479. Hanahan, D.J. 1986 Platelet activating factor...
Fa
Fig. 5.6 The HDL pathway. Lipid-poor apoAI or pre-pi HDL acquires phospholipids PL and free cholesterol FC by interaction with cell membranes, forming discoidal HDL in the circulation. Through the action of lecithin-cholesterol acyltransferase LCAT , and the acquisition of further lipids arising during the action of lipoprotein lipase LPL on triacylglycerol-rich particles TRL phospholipid transfer protein, PLTP, is involved in this transfer , these particles swell and become spherical 'mature...
The Catabolism Of Acylglycerols
This section is concerned entirely with the hydrolysis of fatty acids from one or more positions on the glycerol backbone of acylglycerols, catalysed by enzymes termed lipases, which act mainly at the surfaces of large fat particles. Catabolism refers to the metabolic breakdown of complex biological molecules. One of the main themes running through this book is that, with very few exceptions, lipids in biological tissues are in a dynamic state they are continually being synthesized and broken...
Summary Lut
Glycerolipids are based on the trihydric alcohol glycerol. Phosphoglycerides are synthesized in one of three basic pathways. Either a CDP-base derivative reacts with diacylglycerol to produce the phospholipid or CDP-diacylglycerol can be used as an intermediate. The third type of pathway involves the conversion of one phospholipid into another. As a generalization, phosphatidylcholine and phosphatidylethanolamine are made by the CDP-base pathway in eukaryotes while the CDP-diacylglycerol...
The monoacylglycerol pathway is important mainly in rebuilding TAG from
The main function of the monoacylglycerol pathway Fig. 3.6 is to resynthesize TAG from the monoacylglycerols formed during the digestion of fats in the small intestine. Therefore, this mechanism is one by which existing TAG are modified rather than one by which new fat is formed Section 5.1.3 . During the hydrolysis of dietary TAG in the intestinal lumen by pancreatic lipase, the fatty acids in positions 1 and 3 are preferentially removed. The remaining 2-monoacylglycerols are relatively...
Ch I
ACC is a Type I biotin-containing enzyme. Such enzymes catalyse carboxylation reactions in two main steps 1. ATP HCO BCCP. biotin - ADP Pi BCCP-COO Net ATP HCO3 acetyl-CoA ADP Pi malonyl-CoA Actually, each of the main reactions takes place in steps and these are described in Knowles7 1989 review see Further Reading. The carboxylate group is attached to a nitrogen on the biotin moiety, which aids in its transfer to acetyl-CoA. ACCs can have a multienzyme structure or exist as multifunctional...
A few dietary lipids may be toxic
Much of the discussion in this chapier is concerned with the positive contributions made by dietary lipids, especially fatty acids, to nutrition and health. It is equally important to consider whether dietary lipids can also have adverse or toxic effects. Of the fatty acids, those containing a cyclopropene ring Section 2.1.4 have been considered toxic as a result of their ability to inhibit the A9-desaturase. One result of this is to alter membrane permeability as seen in 'pink-white disease'....
Lipid Biochemistry
School of Biosciences, Cardiff University, Cardiff Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Oxford 1971, 1975, 1980 Michael I. Gurr and A.T. James 1991 Michael I. Gurr and John L. Harwood 2002 Michael I. Gurr, John L. Harwood and Keith N. Frayn Blackwell Science Ltd, a Blackwell Publishing Company Editorial Offices Tel 44 0 1865 206206 Blackwell Science, Inc., 350 Main Street, Malden, MA 02148-5018, USA Tel 1 781 388 8250 Iowa State Press, a Blackwell...
Biohydrogenation of unsaturated fatty acids takes place in rumen microorganisms
Desaturation of an acyl chain is a reaction widespread in Nature. The reverse process, namely the hydrogenation of double bonds, is found in only a few organisms. These organisms are commonly found in the rumens of cows, sheep and other ruminant animals. Linoleic acid, for example, can be hydrogenated by rumen flora anaerobic bacteria and protozoa to stearic acid by a series of reactions shown in Fig. 2.22. First of all the substrate fatty acids must be released from leaf complex lipids by the...
B
Fig. 3.5 A proposed scheme for the formation of oil bodies. Oil bodies probably bud off from the ER as small TAG droplets of 60-100 nm diameter. Such small oil droplets are unstable in aqueous media and would tend to coalesce, rapidly at first and then more slowly until reaching a stable size. A In the absence of oleosins and in non-desiccating tissues like palm mesocarp, the final oil body size is about 10-25 p.m. B Directly after their synthesis, oleosins are inserted into the ER membrane,...