Lipids functional groups

Covalent attachment of proteins to the surface of liposomal bilayers is done through reactive sites created on the head groups of phospholipids with the intermediary use of a crosslinker or other activating agent. The lipid functional groups described in Section 1 of this chapter are modified according to the methods discussed in Section 2 to be reactive toward specific target... 

The following sections present suggested protocols for creating protein-bearing liposomes. Each method utilizes specific lipid functional groups and targets amines, sulfhydryls, aldehydes, or carboxylates on the protein molecules. 

Fig. 5.—Proposed Structure of the Lipid Functional Group of the Group C Meningococcal Polysaccharide. 

The only piece of experimental evidence for the orientation of apoA-I helices on DMPC discoidal complexes has come from the use of polarized attenuated total reflection infrared (ATR-IR) spectroscopy (Brasseur et al. (1990 Wald et al., 1990). Although internal reflection spectroscopy is not new (Harrick, 1967), its combination with polarized IR measurements of oriented biological membranes is a more recent application, which allows the spectrum to be taken in the presence of water. The technique has been used most frequently to study the orientation of lipid functional groups relative to the membrane plane in pure lipid bilayers (Fringeli and Gunthard, 1981 Holmgre et al., 1987 Okamura et al., 1990 Hubner and Mantsch, 1991), but has also been applied to studies of... 

We ll see numerous instances in future chapters where the chemistry of a given functional group is strongly affected by being in a ring rather than an open chain. Because cyclic molecules are so commonly encountered in all classes of bioniolecules, including proteins, lipids, carbohydrates, and nucleic acids, it s important that the effects of their cyclic structures be understood. 

Fig. 3-12 Lipids consist of a triglyceride, three fatty acids such as those in (a) joined to glycerol (b). Other lipids include other functional groups such as phosphate derivatives (c). (Reprinted with permission from W. K. Purves and G. H. Orians, "Life The Science of Biology," pp. 63-81, Copyright 1987 by Sinauer Associates, Inc., Simderland, MA.)...

Comprehensive Organic Chemistry , Pergamon, Elmsford, NY, 1979, is a six-volume treatise on the synthesis and reactions of organic compounds. The first three volumes cover the various functional groups, vol. 4, heterocyclic compounds, and vol. 5, biological compounds such as proteins, carbohydrates, and lipids. Probably the most useful volume is vol. 6, which contains formula, subject, and author indexes, as well as indexes of reactions and... 

The reagent used for the deteetion may be speeifie to a special functional group or specific lipids or may be a nonspecific reagent that makes all hpids visible. The most commonly used reagent that is nonspecific for any lipid group is 0.1% (w/v) 2, 7 -dichlorofuorescein in 95% methanol. This is mainly useful when the plates have been developed in acidic solvents. The lipid spots or bands can be visualized as yellow spots or bands under UV light. After the plates are developed in alkaline solvents, an aqueous solution of Rhodamine 6G (0.01%) can be used, and lipid spots can be seen as pink spots under UV. Because both these methods are nondestructive, they can be effectively used in PTLC so that the separated sample bands can be scraped off and used for further analysis. 

In contrast to MDA and hydroxynonenai, other aldehyde products of lipid peroxidation are hydrophobic and remain closely associated with LDL to accumulate to mil-limolar concentrations. Aldehydes at these elevated levels react with the protein portion of the LDL molecule, apolipoprotein B (apoB). Accumulated aldehydes bind the free amino groups from lysine residues in addition to other functional groups (-OH, -SH) on the apoB polypeptide. Consequently, the protein takes on a net negative charge and complete structural rearrangement results in the formation of ox-LDL. ox-LDL is no longer recognized by the LDL receptor, and has several pro-inflammatory properties (discussed below). 

Biosorption is a rather complex process affected by several factors that include different binding mechanisms (Figure 10.4). Most of the functional groups responsible for metal binding are found in cell walls and include carboxyl, hydroxyl, sulfate, sulfhydryl, phosphate, amino, amide, imine, and imidazol moieties.4 90 The cell wall of plant biomass has proteins, lipids, carbohydrate polymers (cellulose, xylane, mannan, etc.), and inorganic ions of Ca(II), Mg(II), and so on. The carboxylic and phosphate groups in the cell wall are the main acidic functional groups that affect directly the adsorption capacity of the biomass.101... 

Fig. 11 Methods for the construction of PEGylated liposomes, (a) Liposomes possessing reactive groups, such as amino and carboxyl groups, can be prepared by incorporating lipophilic components containing these functional groups into a bilayer membrane. Functionalized liposomes can be PEGylated by reaction with activated PEG derivatives, (b) Preparation of PEGylated liposomes using PEG derivatives possessing lipid moieties...

Figure 22.9 The major functional groups of lipids that may participate in bioconjugate techniques include amines, carboxylates, and hydroxyls.

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