Fatty acid specific

A variety of cellular and viral proteins contain fatty acids covalently bound via ester linkages to the side chains of cysteine and sometimes to serine or threonine residues within a polypeptide chain (Figure 9.18). This type of fatty acyl chain linkage has a broader fatty acid specificity than A myristoylation. Myristate, palmitate, stearate, and oleate can all be esterified in this way, with the Cjg and Cjg chain lengths being most commonly found. Proteins anchored to membranes via fatty acyl thioesters include G-protein-coupled receptors, the surface glycoproteins of several viruses, and the transferrin receptor protein. 

The unit can perform the neutralization of most organic acids, including natural and synthetic fatty acids, specifically those resulting from the sulf-(on)ation of alkylates, alcohols, ethoxylated alcohols, and so forth, to obtain natural product at high concentration. 

Also Enterobacteria are able to synthesize unsaturated fatty acids and to incorporate these into the lipid A component. Thus, when grown at low temperature (10- 15°C) E. coli (143), Salmonella spp. (142), P. mirabilis (37), and Y. enterocolitica (145) are incorporated into the lipid A component unsaturated fatty acids that are not present in LPS of bacteria grown at 370 C. For E. coli and Salmonella strains grown at low temperatures, it was found that (Z)-A9-hexadecenoic acid (A9-16 1) was incorporated at the expense of 12 0 (142,143), however, not quantitatively. Further investigations of these lipid A by l.d.-m.s. revealed that the unsaturated fatty acid specifically replaced the 12 0 residue in 14 0[3-6>( 12 0)] that is bound to GlcN(II) (37). A similar effect of thermoadaptation, resulting in the formation of amide-bound 14 0[3-6>(A9-16 1)], was detected in P. mirabilis and Y. enterocolitica (145). 

Figure 2. Specific immunoabsorbents for Salmonella O and R form antibodies. Key PS, O-specific polysaccharide, core, core fragment and GlcNHr glucosamine and fatty acids. Specific immunoabsorbents for lipid A antibodies have also been prepared (C. Galanos and D. Nerkar, unpublished results Luderitz et a ., 1982).

Sugano, M., and Portman, O. W., Fatty acid specificities and rates of cholesterol esterification in vivo and in vitro. Arch. Biochem. Biofihys. 107, 341-351 (1964). 

The fats and oils standards aim to provide protection in terms of authenticity of the products covered and contain descriptions of each. They also recognize that the fatty acid composition is one of the main ways of identifying and distinguishing one oil/fat from another. Fatty acid specifications for each oil/fat are included as essential composition and quality factors and are reproduced in Tables 8.6 and 8.7. For vegetable oils, it is also recognized that other compositional factors may be used to assist in assessing authenticity—iodine... 

Table 8.6 Codex fatty acid specifications for animal fats (% total fatty acids)...

Cooper, S.M., Grigor, M.R. 1980. Fatty acid specificities of microsomal acyltransferases esterifying positions-1 and -2 of acylglycerols in mammary glands from lactating rats. Biochem. J. 187, 289-295. 

LPL exhibits no fatty acid specificity during hydrolysis of mixed triglycerides but does have strong positional specificity (Morley and Kuksis, 1977). It acts on primary ester bonds with some preference for the sn-1 over the sn-3 position of triglycerides (Somerharju et al., 1978) and can hydrolyze 2-monoglycerides only after their conversion to the sn-1 or sn-3 isomers (Nilsson-Ehle et al., 1973). It shows phospholipase Ai activity on phosphatidyl choline (i.e., it hydrolyzes the primary ester bond at the sn-1 position). This contrasts with most phospholipases A, which exhibit A2 activitiy. 

Penicillium roqueforti and P. camemberti produce very active extracellular lipases, which are the principal lipolytic agents in mold-ripened cheeses. They preferentially hydrolyze the short-chain fatty acids in milk fat. P. roqueforti produces two lipases, one with an alkaline pH optimum and the other most active at pH 6 6.5, with slightly differing fatty acid specificities (Menassa and Lamberet, 1982). P. camemberti secretes a single lipase with optimal activity at pH 9 (Lamberet and Lenoir, 1976). 

Baillargeon, M.W., McCarthy, S.G. 1991. Geotrichum candidum NRRL Y-553 lipase purification, characterization and fatty acid specificity. Lipids 26, 831-836. 

Morley, N., Kuksis, A. 1977. Lack of fatty acid specificity in the lipolysis of oligo- and polyunsaturated triacylglycerols by milk lipoprotein lipase. Biochim. Biophys. Acta 487, 332-342. 

Figure 25.3 shows the MS3 spectrum of [ROR + Li - RCOOH]+ at m/z 625.5. Regiospecific ions were derived from the loss of a,(3-unsaturated fatty acids specific at the sn-2 position (Hsu and Turk 1999) and were the two ions of [ROR + Li - RCOOH - 0 CH=CHC00H]+ at m/z 345.2 and [RRO and/or ORR + Li - RCOOH - R CH=CHCOOH]+ at m/z 329.3. The abundance of the latter ion was very low (Fig. 25.3). It seems that the oleoyl moiety of ROR (non-stereospecific) in castor oil was mostly at the sn-2 position according to the relative abundances of m/z 345.2 and 329.3. However, most of m/z 345.2 was [ROR + Li - RCOOH - R"CH=C=0]+, from the loss of ketene, not [ROR + Li - RCOOH - 0 CH=CHC00H]+. The ratio of these two ions at m/z 345.2 and identification of the ion resulting from the loss of ketene will be given in a latter section. The fragmentation pathway of the loss of a,(3-unsaturated fatty acids specific at sn-2 position has been proposed previously as shown in Figure 25.4A (Hsu and Turk, 1999).

From the relative abundances of the two ions derived from the loss of a,(S-unsaturated fatty acids specific at the sn-2 position for each of the other RRAc in castor oil, we estimated the content of the 1,3-diricinolcoyl-2-acyl-sn-glycerol species among the three isomers as follows RLR (95%), RLnR (96%), RSR (96%), RPR (78%), and RLsR (31%). These values fall consistently within +3% in repeated experiments. Both MS3 and CAD-MS2 were used to measure the content of each l,3-diricinoleoyl-2-acyl-5,n-glycerol among the three possible stereoisomers with equivalent results (data not shown). 

The temperature optimum for interesterification is 85°C or higher, and the half-life in continuous acidolysis of spy bean oil with lauric acid at 60°C is above 2500 h. The non-specificity makes the catalyst useful in random interesterification of different fats. The catalyst has some saturated fatty acid specificity. Two lipase components (A and B) were purified. Lipase A is important for interesterification, and Lipase B is important in ester synthesis. 

The fatty acid specificity in the acidolysis reaction has been examined (Table IV). 

The fatty acid specificity of the immobilized Lipase A has been compared with the specificity of the crude enzyme by the method described earlier (Table IX). 

Table IX. Fatty Acid Specificity of Lipase A and the Crude Enzyme...

This fatty acid specificity may lead to the assumption that the activity in acidolysis of polyunsaturated fatty acids would be negligible. We have tested the incorporation of polyunsaturated fatty acids isolated from menhaden oil into trilaurin, and found that both immobilized Lipase A and the immobilized crude enzyme are quite active, and more active than the immobilized Mucor miehei lipase (Lipozyme). 

It is important to note that animals are unable to effect the net synthesis of glucose from fatty acids. Specifically, acetyl CoA cannot be converted into pyruvate or oxaloacetate in animals. The two carbon atoms of the acetyl group of acetyl CoA enter the citric acid cycle, but two carbon atoms leave the cycle in the decarboxylations catalyzed by isocitrate dehydrogenase and a-ketoglutarate dehydrogenase. Consequently, oxaloacetate is regenerated, but it is not formed de novo when the acetyl unit of acetyl CoA is oxidized by the citric acid cycle. In contrast, plants have two additional enzymes enabling them to convert the carbon atoms of acetyl CoA into oxaloacetate (Section 17.4.). 

Specificity is one of the most striking properties of enzyme molecules. Enzyme specificity can be defined as a comparative difference in rates of catalysis of certain reactions. After an enzyme is identified as a hpase, several specificities within the class are identified or can be expected to occur. The main advantage of lipases, which differentiate enzymatic reactions from chemically-catalyzed reactions, is lipase specificity. Lipases have turned out to be very useful enzymes for catalyzing various types of reactions with a rather wide substrate specificity. The fatty acid specificity of lipases has been exploited to produce structured lipids and to enrich lipids with specific fatty acids to improve the nutritional characteristics of lipids (24). Certain lipases display positional specificity (regiospecificity) toward fatty acyl groups in a TAG molecule as well as fatty acid selectivity. 

Microbial lipases from Aspergillus niger (AN), Candida cylindracea (CC), Pseudomonas spp. (PS), Chromobacterium viscosum (CV), Rhizopus delemer (RD), and Rhizopus javanicus (RJ) have been widely used in modifying PUFA-rich oils (117). The fatty acid specificity of lipases (discrimination of PUFA over short-chain fatty acids) is a crucial factor when considering the application of enzymes to modify marine oils rich in PUFA (118-121). Lipases from Rhizopus spp are known to be 1,3-position specific (122). Wanasundara (79) and Wanasundara and Shahidi (123, 124) (seal blubber oil SBO and menhaden oil MHO) and Tanaka et al. (117)... 

Platelet phospholipid and fatty acid composition was first reported in some detail by two groups (11, 12). Subsequently, our laboratory fully characterized individual fatty acid specific molecular species in human platelet phospholipids (13), in addition to documenting the molar concentration of individual phospholipids (Table 1). This work... 

Most of the latest publications on NRPS substrate specificity are focused on A domain specificity because their substrate screening is straightforward in terms of biosynthetic substrate form (free amino acids/fatty acids/aryl acids) and T domain substrates (one T domain). Four studies focus on substrate specificity of NRPS loading modules of microcystin biosynthesis,97 mycosubtilin biosynthesis,51 daptomycin biosynthesis,108 and leinamycin biosynthesis.108 The A domains of microcystin, mycosubtilin, and daptomycin biosynthesis initiation showed fatty acid specificity. The initial domain from leinamycin biosynthesis has D-amino acid specificity. Another paper presents the elucidation of aryl acid-specific AsbC adenylation enzyme from petrobactin biosynthesis.104... 

The recent studies of Hansen et al51 and Wittmann et al,109 revealed a new mechanism for lipidation of lipopeptide biosynthesis such as mycosubtilin or daptomycin biosynthesis by application of ESI-FTMS. Both papers describe that fatty acid incorporation is catalyzed by an A domain with fatty acid specificity in the loading module of the mycosubtilin NRPS (Figure 15) or by a preassembly line A and T domain in daptomycin biosynthesis (Figure 16). 

We have reported that there exists an apparent fatty acid specificity for palmitate and oleate for the FAEEs present in the blood following ethanol intake and that FAEE synthesis increases with higher extracellular concentrations of their corresponding fatty acids for ethyl oleate, ethyl linoleate, and ethyl arachidonate—but not ethyl palmitate (Dan, 1997). Using HepG2 cells incubated with ethanol, we have also quantitated the actual mass of FAEE synthesized and demonstrated that the fatty acid used for FAEE synthesis is derived from a designated intracellular pool of fatty acids (Dan, 1998). 

In vitro assay systems can also be used to show that ACAT uses oleoyl-CoA and palmitoyl-CoA preferentially as substrates [15,16,22]. This specificity is in good agreement with the fatty acid composition typically found upon analysis of tissue CE. However, some tissues, such as the rat adrenal, ovary, and testis, are rich in polyunsaturated fatty acids, raising the possibility that these tissues may contain an ACAT enzyme with a different fatty acid specificity [23]. 

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