Membrane lipid biosynthesis

Substituted pyridazinone herbicides directly inhibit photosystem II, chloroplast pigment biosynthesis, and membrane lipid biosynthesis. Depending on the substitution, pyridazinones can specifically inhibit the synthesis of linolenic acid in galacto-lipids and phospholipids preferentially alter the fatty acid composition of monogalactosyl diglycerides compared with digalactosyl diglycerides and cause a build-up of saturated fatty acids in the chloroplast membranes. 

The following is a partial list of the uses of ATP or an energetically equivalent NTP (1) to produce the macromolecules nucleic acids, proteins, and polysaccharides (2) to produce the organelles and membranes (lipid biosynthesis) ... 

CDP-chollna cytidine diphosphate choline. See Membrane lipids (biosynthesis). 

Cytidine diphosphocholine, CDP-choline, active choline the activated form of choline, which is biosynthesized from phosphocholine and CTP. See Membrane lipids (biosynthesis). 

Henry S.A. (1982) Membrane lipids of yeast biochemical mid genetic studies. In The Molecular Biology of the Yeast Saccharomyces, vol. 2. Metabolism and Biosynthesis (eds J.N. Strathem, E.W. Jones J.R. Broach), pp. 101-158. Cold Spring Harbor, NY Cold Spring Harbor Laboratory. 

The levels of PAF synthesis and release are also modulated by levels of extracellular albumin. In the absence of albumin, neutrophils (stimulated with fMet-Leu-Phe) synthesise only low levels of PAF within 1-2 min of stimulation. In the presence of 0.25% albumin, PAF synthesis is increased, and up to half of this may be released with 5% albumin, rates of synthesis and release are increased further and sustained over a 30-min period. Newly-synthesised PAF is reincorporated by neutrophils into membrane lipids and is therefore poorly soluble in aqueous media. Thus, extracellularly added albumin will bind to cell-associated PAF and effectively solubilise it at concentrations below its critical micellar concentration (CMC). This will effectively enhance the PAF release rate, which will decrease the concentration of cell-associated PAF thus, the rate of biosynthesis will be sustained. 

Once synthesized several factors influence the particular leaflet of the membrane lipid bilayer where the lipids reside. One is static interactions with intrinsic and extrinsic membrane proteins which, by virtue of their mechanism of biosynthesis, are also asymmetric with respect to the membrane. The interaction of the cytoplasmic protein, spectrin with the erythrocye membrane has been the subject of a number of studies. Coupling of spectrin to the transmembrane proteins, band 3 and glycophorin 3 via ankyrin and protein 4.1, respectively, has been well documented (van Doit et al, 1998). Interaction of spectrin with membrane lipids is still somewhat conjectural but recent studies have characterized such interactions more precisely. O Toole et al. (2000) have used a fluorescine derivative of phosphatidylethanolamine to investigate the binding affinity of specttin to lipid bilayers comprised of phosphatidylcholine or a binary mixture of phosphatidylcholine and phosphatidylserine. They concluded on the basis... 

Enzymatic catalysis of reactions. Important enzymes are located in membranes at the interface between the lipid and aqueous phases. This is where reactions with apolar substrates occur. Examples include lipid biosynthesis (see p. 170) and the metabolism of apolar xenobiotics (see p. 316). The most important reactions in energy conversion—i.e., oxidative phosphorylation (see... 

Kakinuma, K. Yamagishi, M. Fujimoto, Y. Ikckawa, N. Oshima, T. (1988) Stereochemistry of the biosynthesis of sn-2,3-0-diphytanyl glycerol, membrane lipid of Archaebacteria Halobacterium halobium. J. Am. Chem. Soc., 110,4861-3. 

Kates, M. (1993) Biology of halophilic bacteria, II. Membrane lipids of extreme halr hiles biosynthesis, function and evolutionary significance. Experientia, 49, 1027-36. 

Pereto, Y., Lopez-Garcia, R, and Moreira, D. (2004). Ancestral lipid biosynthesis and early membrane evolution. Trends Biochem. Sci., 29,469-77. 

This three-step process for transferring fatty acids into the mitochondrion—esterification to CoA, transesterification to carnitine followed by transport, and transesterification back to CoA—links two separate pools of coenzyme A and of fatty acyl-CoA, one in the cytosol, the other in mitochondria These pools have different functions. Coenzyme A in the mitochondrial matrix is largely used in oxidative degradation of pyruvate, fatty acids, and some amino acids, whereas cytosolic coenzyme A is used in the biosynthesis of fatty acids (see Fig. 21-10). Fatty acyl-CoA in the cytosolic pool can be used for membrane lipid synthesis or can be moved into the mitochondrial matrix for oxidation and ATP production. Conversion to the carnitine ester commits the fatty acyl moiety to the oxidative fate. 

Structure and Functions of Biological Membranes 381 Metabolism of Fatty Acids 411 Biosynthesis of Membrane Lipids 436 Metabolism of Cholesterol 459... 

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