Lipid metabolism fatty-acid biosynthesis

Many aroma compounds in fruits and plant materials are derived from lipid metabolism. Fatty acid biosynthesis and degradation and their connections with glycolysis, gluconeogenesis, TCA cycle, glyoxylate cycle and terpene metabolism have been described by Lynen (2) and Stumpf ( ). During fatty acid biosynthesis in the cytoplasm acetyl-CoA is transformed into malonyl-CoA. The de novo synthesis of palmitic acid by palmitoyl-ACP synthetase involves the sequential addition of C2-units by a series of reactions which have been well characterized. Palmitoyl-ACP is transformed into stearoyl-ACP and oleoyl-CoA in chloroplasts and plastides. During B-oxi-dation in mitochondria and microsomes the fatty acids are bound to CoASH. The B-oxidation pathway shows a similar reaction sequence compared to that of de novo synthesis. B-Oxidation and de novo synthesis possess differences in activation, coenzymes, enzymes and the intermediates (SM+)-3-hydroxyacyl-S-CoA (B-oxidation) and (R)-(-)-3-hydroxyacyl-ACP (de novo synthesis). The key enzyme for de novo synthesis (acetyl-CoA carboxylase) is inhibited by palmitoyl-S-CoA and plays an important role in fatty acid metabolism. 

A natural question is "Why has this complex pathway evolved to do something that could have been done much more directly " One possibility is that the presence of too much malonyl-CoA, the product of the P oxidation pathway of propionate metabolism (Fig. 17-3, pathways a and c), would interfere with lipid metabolism. Malonyl-CoA is formed in the cytosol during fatty acid biosynthesis and retards mitochondrial P oxidation by inhibiting carnitine palmitoyltransferase i.46 70a 75 However, a relationship to mitochondrial propionate catabolism is not clear. 

Mutations in desatl affect HC, resulting in a very large decrease in 7-HC in males, and in 7- and 7,11-HC in females, with a parallel increase in saturated HC synthesis (Labeur el al., 2002 Ueyama el al., 2005 Marcillac et al., 2005a,b). Lipid metabolism is impaired too, with both quantitatively and qualitatively altered fatty acid biosynthesis the overall quantity of fatty acids was shown to be reduced by half and that of vaccenic acid, the common precursor to 7-HC in both sexes, reduced by a factor of six in a desatl mutant (Ueyama et al., 2005). 

Ohlrogge, J. B., J. G. Jaworski, and D. Post-Beittenmiller, De novo fatty acid biosynthesis, in Lipid Metabolism in Plants (T. S. Moore, Jr., ed.) 3-32, CRC Press, Boca Raton, FL, 1993. 

His work has been done in the Faculty of Ciencias Exactas at Buenos Aires University. I personally had the pleasure of working in his laboratory and there began in 1946 several studies on lipids. First we studied fish lipids and waxes. Then we started a series of research projects on polyunsaturated fatty acid biosynthesis in different species of the animal kingdom as well as on the lipid metabolism and the effect of diabetes on tumor cells. Our group, the oldest in continuous research in lipid biochemistry, developed in the Catedra de Bioquimica of the Institute de Fisiologia of the Faculty of Medicine of La Plata University. To this group belong... 

Many studies have revealed that thyroid hormones markedly affect lipid metabolism in man and in several species of animals. Concerning fatty acid biosynthesis it was demonstrated that the administration of thyroxine stimulates the incorporation of l-l c acetate into fatty acids in rats and mice (Dayton et al, I960) (Gompertz and Greenbaum, 1966) (March and Mayer, 1959). According to Gompertz and Greenbaum (1966) these observations appear to be associated with an increase of stearyl-CoA desaturase activity. Moreover Myant and Iliffe (1963) found that rats treated with thyroxine showed an inhibition of acetate incorporation, but not of malonate incorporation, into fatty acids by mitochondria free, subcellular liver preparations. Other authors have shown that the thyrotoxic state was accompanied by an increased incorporation of acetyl-CoA to fatty acid and a rise in the activity of fatty acid synthetase in rat livers (Diamant et al, 1972) (Roncari and Murthy, 1975). However, in vitro studies of fatty acid synthesis in which liver supernatant of 105,000 xg and microsomal preparations were incubated with the hormone showed that thyroxine inhibits de novo synthesis of palmitate and stimulates the desaturation reactions (Faas et al, 1972). 

Besides the inhibition of fatty acid biosynthesis the cyclohexane-1,3-dione derivates e.g. sethoxydim (Fig.3) also induce several other alterations of the plant composition and metabolism. Due to the herbicide-induced inhibition of fatty acid and biomembrane lipid formation, the development of functional chloroplasts, the formation of thylakoids and the chloroplast replication are also blocked (Lichtenthaler 1984, Lichtenthaler and Meier 1984) as well as the accumulation of chlorophylls and carotenoids (Lichtenthaler 1987, Lichtenthaler et al. 1987) but not their biosynthesis (Lichtenthaler 1987). This resulted in the formation of white leaf parts which are free of photosynthetic pigments. Furthermore, in herbicide-treated maize shoots the accumulation and biosynthesis of plastidic and cytoplasmic phospho- and glykolipids was blocked (Burgstahler and Lichtenthaler 1984 and Burgstahler 1985). The cyclohexane-1,3-dione derivatives block the... 

When nystatin was added to the growing mycelium in the intensive growing phase, the effect of the antibiotic on the lipid metabolism can better be seen. Sensitivity is followed by the relative decrease of linoleic and stearic acids and the relative increase of palmitic and linolenic acids. These changes and the Increased anrx)unt of the shorter fatty acids suggest that the Inhibition in the fatty acid biosynthesis is responsible for the sensitivity of the nrK)uids to saponin or polyene antibiotics. 

Thus, of the overall 20 metabolic pathways involved in Lipid and Fatty Acid Metabolism, there are 13 such pathways which are exclusively restricted to L. major, of which only 7 pathways had the enzymes and reactions unique to L. major. From the Table 1 it is found that the maximum number of the genes and the resultant gene products (enzymes), distinctive to the L. major are specifically engaged in the LPG and GIPL Biosynthesis Pathway followed by the fatty add metabolism... 

Ifl. A. R. Slabas, 3. Harding, A. Hellyer, C. Sidebottom, H. Gwynne, R. Kessell and M. P. Tombs, Enzymology of plant fatty acid biosynthesis, m "Structure, Function and Metabolism of Plant Lipids", P. A. Siegenthaler and W. Eichenberger, eds., Elsevier Science Publishers, Amsterdam (198 ). 

References. 1. B. Liedvogel, Acetyl coenzyme A and isopentenylpyro-phosphate as lipid precursors in plant cells - biosynthesis and compartmen-tation, J. Plant Physiol. 214 211 (1986). 2. P.K. Stumpf, Fatty acid biosynthesis in higher plants, "Fatty Acid Metabolism and Its Regulation",... 

In conclusion, C. antlqua is unique in lipid and fatty acid composition. Studies on chromophytan lipid metabolism will shed new light on the biosynthesis of molecular species of lipids especially those which contain C2Q unsaturated acids. 

We are Interested In the regulation of fatty acid biosynthesis and how the levels of proteins In this pathway are controlled. The central role of ACP In lipid metabolism and Its well characterized structure led us to choose this protein as a representative marker of the fatty acid biosynthetic pathway. Our approach has been to examine the structure and expression of ACP In detail with the expectation that this will reveal some of the general control mechanisms which regulate plant fatty acid biosynthesis. 

FATP5 KO mice have been characterized in two studies focusing on the role of FATP5 in hepatic lipid and bile metabolism. LCFA uptake in primary hepato-cytes isolated from FATP5 KO mice was reduced by 50% and hepatic lipid content in the KO mice was significantly reduced despite an increased fatty acid de novo biosynthesis. Detailed analysis of the hepatic lipidome of FATP5 KO mice revealed significant... 

Ketosis is a pathologic state produced by an excess of ketone bodies in the organism. However, ketosis may be regarded as a lipid metabolism pathology with a certain reserve, since excessive biosynthesis of ketone bodies in the liver is sequent upon an intensive hepatic oxidation not only of fatty acids, but also of keto-genic amino acids. The breakdown of the carbon frameworks of these amino acids leads to the formation of acetyl-CoA and acetoacetyl-CoA, which are used in... 

Cholesterol is present in all animal tissues, and particularly in neural tissue. It is a major constituent of cellular membranes, in which it regulates fluidity (see p. 216). The storage and transport forms of cholesterol are its esters with fatty acids. In lipoproteins, cholesterol and its fatty acid esters are associated with other lipids (see p.278). Cholesterol is a constituent of the bile and is therefore found in many gallstones. Its biosynthesis, metabolism, and transport are discussed elsewhere (see pp. 172, 312). 

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