Lipid phosphate groups

Probing Ca++—Phosphate Binding. Although this question has been at the center of the current investigations, little experimentation was reported on direct evidence which could be furnished by IR spectroscopy. In a brief mention of IR absorption of DPL-uranyl nitrate in nujol paste, it was concluded that indeed Ca++ interacts with the lipid phosphate group (7). Subsequently, after thermodynamic analysis of calorimetric studies with DPL dispersions in aqueous electrolyte, the same laboratory suggested the absence of direct Ca++-phosphate interaction (8). Strangely, the authors of the second work (8) failed to provide explanations for the discrepancy between this and a previous report (7). The particular predicament implies that either one of the two experiments had to be... 

Longer incubation of the GUV-peptide mixture results in the higher-order membrane cluster products shown in Figure 30.3(B) and (C). One possible explanation of this effect is complementary charge saturation of charged lysines and the lipid phosphate groups. The helical structure of the peptide results in a stacked order of the lysines (Figure 30.3(D)) which would mediate membrane-membrane adhesion. 

The intracellular and plasma membranes have a complex structure. The main components of a membrane are lipids (or phospholipids) and different proteins. Lipids are fatlike substances representing the esters of one di- or trivalent alcohol and two aliphatic fatty acid molecules (with 14 to 24 carbon atoms). In phospholipids, phosphoric acid residues, -0-P0(0 )-O-, are located close to the ester links, -C0-0-. The lipid or phospholipid molecules have the form of a compact polar head (the ester and phosphate groups) and two parallel, long nonpolar tails (the hydrocarbon chains of the fatty acids). The polar head is hydrophihc and readily interacts with water the hydrocarbon tails to the... 

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... 

Acidic Lipids (negatively charged—remember the negative charge on the phosphate group) ... 

Figure 13. The overall density (volume fraction) profile for DMPC bilayers is shown here. Apart from the distribution of the overall DMPC molecules, the density distribution of the head-group units (including the choline group, the phosphate group and the oxygens of the glycerol unit), and the end groups of the lipid tails are also indicated. In addition, the free-volume profile and the water profile are depicted...

Figure 14. Volume-fraction profiles of parts of the DMPC molecules for lipids that have the head group at positive coordinates (continuous lines) and at negative coordinates (dashed lines). The centre of the bilayer is positioned at z — 0. The phosphate group, the nitrogen of the choline group and the CH3 groups of the tail ends, as well as the other hydrocarbon units, are indicated...

Figure 21. The area per molecule (left ordinate) and the distance between the phosphate groups on opposite sides of the bilayer of the PC and PS lipids as indicated (right ordinate) as a function of the fraction of PS molecules in equilibrated bilayers composed of mixtures of C PC and C PS lipids. Reproduced from ref (85) with permission from the American Chemical Society...

Fig. 2.—Chemical structure of lipid A of the Escherichia coli Re mutant strain F515. The hydroxyl group at position 6 constitutes the attachment site of Kdo. The numbers in circles indicate the number of carbon atoms present in the fatty acyl chains. The 14 0(3-OH) residues possess the (Reconfiguration. The glycosylic phosphate group may be substituted by a phosphate group (see Table I) (46,65,69).

As these results and Fig. 2 show, three structural components may be defined in lipid A (/) the lipid A backbone consisting of a pyranosidic HexN disaccharide and phosphate groups, (ii) substituents of the backbone phosphate residues (polar head groups), and (iii) fatty acids. Therefore, lipid A of different bacteria may be classified according to the nature of the backbone constituents (GlcpN or GlcpN3N), the type and nature of the polar head groups, and features of the acylation pattern. In a few instances, other backbone substituents have been encountered. These will be described later in conjunction with individual lipid A forms. 

Fig. 3.—Chemical structure of the major component of Campylobacter jejuni lipid A. For details see the text. See also the legend to Fig. 2. For substituents of the phosphate groups see Table I. The a-anomeric phosphate has been tentatively assigned (97).

---