Fatty acid modification

Some proteins can be posttranslationally modified by the addition of prenyl groups. Prenyl groups are long-chain, unsaturated hydrocarbons that are intermediates in isoprenoid synthesis. The farnesyl group has 15 carbons, and the geranylgeranyl has 20 carbons. They are attached to a cysteine residue near the end of the protein as a thiol ether (Protein-S-R). Other proteins can have a long-chain fatty acid (C14=myristoyl, C16=palmitoyl) attached to the amino terminus as an amide. These fatty acid modifications can increase the association of proteins with the membrane. 

As mentioned earlier in this chapter, the choice of collector is very much dependent on the type of copper minerals, as well as the type of gangue minerals present in the natural ore. If the ore contains siliceous gangue minerals, then various fatty acid modifications can be used as the principal collector in plant practice. Ores containing carbonaceous and dolo-mitic gangue minerals, where sulphidization method is used, xanthate collector is used as... 

The fatty acid modification was used in operating plants at Kolwezi, Koumbore and Kakanda. The fatty acid used was hydrolysed palm oil prepared as a mixture consisting of 75% hydrolysed palm oil/21% gas oil/4% Unitol. 

A number of studies have been conducted [1,2] in which different fatty acid modifications were examined. High selectivity and high calcite-dolomite recoveries were obtained with emulsified fatty acid with soda ash and sodium silicate. Table 22.2 shows the results from calcite/dolomite flotation using different fatty acid type collectors and various modifications. 

Lipid biochemical features are changed by fatty acid modification... 

Fatty acid modification has no effect on tumor growth... 

However, similar changes in hpid conposition are possible using a variety of other cell types (Bums and Wagner, 1993) such as an adenocarcinoma (Awad and Specter, 1976), and hepatoma (Wood et al, 1975). The dietary fatty acid modification is not limited to tumor cells, since many tissues of the host are affected (Bums et al., 1983). However, different tissues are modified to varying extents, and because of this it will likely be possible to develop protocols that provide therapeuhc selechvity by producing greater or lesser enrichment of the neoplashc cells with a particular type of fatty acid as compared to normal tissues. We have also demonstrated that L1210 leukemia cells that were fatty acid modified in vivo and then placed into tissue culture maintain their experimentally-induced fatty acid composition for up to 4 days (Bums et al, 1980). Therefore, this is a versahle model. 

Fatty acid modification changes oxidative susceptibility... 

Bums, C. P., and Spector, A. A, 1987, Membrane fatty acid modification in tumor cells a potential therapeutic adjunct, Lipids 22 178-184. 

Justin Stege (Diversa Corporation) discussed the molecular evolution of enzymes for particular pathways, with a focus on the modification of oil composition. Oleochemical applications for such enzymes include applications as biocatalysts for fatty acid modifications. In a program to integrate production and processing, such enzymes can be used to modify the fatty acid content of vegetable oils in planta. Results show that expressing such new enzymes in oilseed crops has resulted in altered oil composition, and that the features may be used to better design plant-based oils for use as biofuels and as improved renewable feedstocks. 

Polymerized fatty acid modification of resins and/or curing agents (e.g., polyamides, amidoamines)... 

The changes in physical properties such as membrane order brought about by fatty acid modification are important. However, for the purposes of studying oxidative events, the change in number of double bonds is central to the strategy since the degree of unsaturation is the major determinant of susceptibility to peroxidation. Most importantly, the degree of unsaturation can be manipulated incrementally in our model. 

There are variations to the above structure such as fatty acid modification but these tend to increase the viscosity significantly thus limiting use in inkjet ink formulations. 

He L, Byun H-S, Smit J, Wilschut J, Bittman RJ. Enantioselective synthesis of a novel trans double bond ceramide analogue via catalytic asymmetric dihydroxylation of an enyne. The role of the trans double bond of ceramide in the fusion of Semliki Forest virus with target membranes. J. Am. Chem. Soc. 1999 121 3897-3903. Broun P, Shanklin J, Whittle E, Somerville C. Catalyic plasticity of fatty acid modification enzymes underlying chemical diversity of plant lipids. Science 1998 282 1315-1317. 

Fusion protein of AKT with an amino-terminal myristoylation signal sequence. This fatty acid modification promotes persistent plasma membrane association and signaling activity. 

The degree of rumen-mediated fatty acid modification varies from species to species. For example, the biohydrogenation of dietary unsaturates is greater in sheep than in cattle, and thus mutton tallow contains 5% to 10% more stearic acid, and a correspondingly lower amount of oleic acid, than beef tallow. Table 1 illustrates this trend, although it is somewhat obscured by the necessarily wide ranges of values reported. 

Mathur, S.N., Simon, L, Lokesh, B.R., Specter, AA. Phospholipid fatty acid modification of rat liver microsomes affects acylcoenzyme A cholesterol acyltransferase activity. Biochem. Biophys. Acta 1983 751 401-411... 

Fatty Acid Modification Elongation of Fatty Acids... 

Jenski LJ, Sturdevant LK, Ehringer WD, Stillwell W. Omega-3 fatty acid modification of membrane structure and function 1. Dietary manipulation of tumor cell susceptibility to cell and complement-mediated lysis. Nutr Cancer 1993 19 135-146. 

Ikemoto A, Kobayashi T, Watanabe S, Okuyama H. Membrane fatty acid modifications of PC12 cells by arachidonate or docosahexaenoate affect neurite outgrowth but not norepinephrine release. Neurochem Res 1997 22(6) 671-678. 

---