Protein-phospholipid complex

Apo A-I is the main structural apolipoprotein on HDL particles it is synthesized in hepatic and enteric cells. Bound phosphatidylcholine and sphingomyelin participate in the creation of protein-phospholipid complexes. 

In support of the possibility to manipulate foam stability by changing the nature of protein assembly in the presence of surfactant, Table 6.3 shows a correlation between molecular parameters of protein-phospholipid complexes and the visual appearance of foams stabilized by them in solutions of different pH. The data indicate that the foams stabilized by complexes of phospholipid liposomes with sodium caseinate exhibit a dramatic increase in stability as compared to the corresponding pure protein foams. (The phospholipid sample by itself did not make fine stable foams at any of the concentrations investigated). 

During cell fractionation, nearly all the cyclopenase activity was found in a fraction containing the cell wall together with the cytoplasmic membrane (83,84). From this fraction, the enzyme could be partially solubilized by detergents (e.g., Triton X-100) to yield a protein-phospholipid complex. By treatment with M-butanol, the solubilized enzyme preparation was split into the lipid fraction and the enzyme protein which retained a considerable part of the total enzyme activity. Compared with that of the membrane-bound enzyme, the substrate affinity of the solubilized protein-lipid complex was decreased, whereas... 

Granda (1964) has studied the sterol binding capacity of the protein phospholipid complex obtained after ether degradation of the low-density serum lipoproteins. In these experiments the water-soluble cholesterol-free lipoproteins were equilibrated with sterols dissolved in heptane. A rapid uptake of cholesterol was noted when human sera were examined this was not observed in chicken sera. 

A contribution to the understanding of lipoprotein metabolism would be the definition of the metabolic role of the lysolecithin-rich d 1.21 lipoprotein. This protein-phospholipid complex may simply represent a degradation product of the high-density lipoprotein after removal of the other lipid moieties. On the other hand, it could be considered as a newly synthesized product from the liver on its way to further lipidation to form a more complete class of lipoproteins. Its possible identity with the apolipoprotein described by Roheim and Eder (1961 Roheim et al., 1964) remains to be established. 

Any calcium chelating agent, e.g. citrate or EDTA, added to blood or plasma will prevent clotting as it prevents the formation of the necessary protein-phospholipid complexes. Such... 

The fatty acids could be carried by proteins by a process similar to the way in which serum albumin binds fatty acid in the bloodstream of mammals. Other types of lipid might be formed into complexes analogous to low-density lipoproteins of the type found in animal tissues, where the lipid core of the lipoprotein is surrounded by a hydrophilic cortex made up of protein, phospholipid, and cholesterol (87). This allows the lipid to be moved in an aqueous environment. The protein of the lipoprotein shell could also act as possible ligands for particular receptors at the membrane of the cell at which the export occurs. The lipoproteins, if they are present, would probably be formed within the endomembrane lumen and would receive the proteins at the endoplasmic reticulum. 

Lipids have several important functions in animal cells, which include serving as structural components of membranes and as a stored source of metabolic fuel (Griner et al., 1993). Eukaryotic cell membranes are composed of a complex array of proteins, phospholipids, sphingolipids, and cholesterol. The relative proportions and fatty acid composition of these components dictate the physical properties of membranes, such as fluidity, surface potential, microdomain structure, and permeability. This in turn regulates the localization and activity of membrane-associated proteins. Assembly of membranes necessitates the coordinate synthesis and catabolism of phospholipids, sterols, and sphingolipids to create the unique properties of a given cellular membrane. This must be an extremely complex process that requires coordination of multiple biosynthetic and degradative enzymes and lipid transport activities. 

Free fatty acids are transported as complexes with serum albumin. Cholesterol, triacylglycerols, and phospholipids are transported as protein-lipid complexes called lipoproteins. Lipoproteins are spherical, with varying amounts and kinds of proteins at their surfaces. The protein components, of which at least ten exist, are called apolipoproteins. Lipoproteins are classified in terms of their density. 

Similarly, supersaturation of saliva with respect to calcium phosphate salts is the driving force of calculus (i.e., mineralized dental plaque) and sialolith (i.e., salivary duct stones ) formation. In these cases, negatively charged phospholipids play a crucial role Ca + ions bind to the negative charges of such lipids, and inorganic phosphate associates with the bound calcium that forms a Ca-phosphate-phospholipid complex, which is an excellent nucleus of calcium-phosphate deposition. Salivary proteins may also play a role in this process because such complex formation occurs predominantly on lipids that are protein associated. The increase of pH facilitates these processes (13). 

D3g-dodecylphosphocholine (DPC) micelles were used to provide a lipid environment. This molecule, which possesses a phosphocholine head group and a single Ci2 hydrocarbon chain, mimics the phospholipid component of lipoprotein surface monolayers. About 40 DPC molecules form a micelle which has molecular weight of about 16 kDa. Thus, the apoLp-IH/DPC (1 1 protein/micelle) complex... 

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