Lipid carrier molecule

The biosynthesis sequence can be divided into three stages synthesis of the precursors in the cytoplasm transfer of the precursors to a lipid carrier molecule which transports them across the membrane insertion into the... 

The most complete structural information about sulfate-dependent protein interactions is available from extensive studies on the many interactions of heparan sulfate proteoglycans (HSPGs). Via their covalently attached heparan sulfate chains, HSPGs bind to a large array of growth factors, cytokines, chemokines, extracellular matrix proteins, cell-cell adhesion molecules, viral attachment receptors, blood coagulation components, and lipid carrier molecules [18 21], Among the functions served by these interactions are ... 

It has been well established that the enzymes required for the biosynthesis of the polymers of the outer membrane are localized in the inner membrane. Most importantly, the lipid-carrier molecules (poly-isoprenoid-phosphates) are found in this membrane. These molecules transfer newly synthesized, activated precursor molecules from the hydrophilic cytoplasmic environment into the lipophilic environment of the membrane, where the assembly into polymeric structures takes place. This assembly process is used for lipopolysaccharides, peptidoglycans, and capsular polysaccharides. In a subsequent step, the membrane-carrier molecules transfer the assembled polymers from the inner to the outer membrane. ... 

The lipid bilayer arrangement of the plasma membrane renders it selectively permeable. Uncharged or nonpolar molecules, such as oxygen, carbon dioxide, and fatty acids, are lipid soluble and may permeate through the membrane quite readily. Charged or polar molecules, such as glucose, proteins, and ions, are water soluble and impermeable, unable to cross the membrane unassisted. These substances require protein channels or carrier molecules to enter or leave the cell. 

The phospholipids thus obtained are transported by lipid-carrier cytoplasmic proteins to the membranes (cellular or intracellular) to replace the used or impaired phospholipid molecules. 

Figure 3. Step 1 in the modified MacFarland bioactivity model Diffusion or carriage by plasma protein from the entry point to the anterior membrane surface (ams) transfer from the first aqueous phase (0 ) to the ams passage through the membrane by diffusion or by lipid soluble membrane carrier molecule bound to the posterior membrane surface (pms) transfer from the pms to the second aqueous phase (02).

As far as the overall dimensions of a membrane-active ion-carrier molecule are concerned, a compromise has to be made. Such molecules have to be large enough to assure lipid solubility and small enough to guarantee mobility. 

Bacitracin inhibits the dephosphorylation of this lipid carrier, a step essential to the carrier molecule s ability to accept cell wall constituents for transport. 

The discriminative uptake of alkali metal cations by biological systems, through their membranes, has been an area of much interest. In the membrane, the cations must pass through a lipid bilayer of low dielectric constant and this has led to the proposition that the cation could be selectively transferred via a carrier molecule, or through a suitably donor-lined pore.7-9 As a consequence of their selective properties, the polyethers and cryptands have been investigated as speculative models for the above process and selectivity sequences have been established. 

A third group of lipid-binding proteins have a four-helix bundle structure. They include the insect lipophorins, which transport diacylglycerols in the hemolymph (see main text), and nonspecific lipid carriers of green plants.q An 87-residue four-helix protein with a more open structure binds acyl-coenzyme A molecules in liver.r... 

Many larger lipid carrier proteins are known. The 476-residue plasma cholesteryl ester transfer protein is discussed briefly in Chapter 22. Plasma phospholipid transfer proteins are of similar size.t/U A 456-residue human phospholipid-binding protein interacts with the lipopolysaccharide of the surfaces of gram-negative bacteria (Fig. 8-30) and participates in the immune response to the bacteria. It has an elongated boomerang shape with two cavities, both of which bind a molecule of phosphatidylcholine. Other plasma lipid transfer proteins may have similar structures/... 

Phospholipids are found in all living cells and typically constitute about half of the mass of animal cell plasma membranes (Cevc, 1992). The reason forthe variety of membrane lipids might simply be that these amphiphilic structures have in common the ability to arrange as bilayers in an aqueous environment (Paltauf and Hermetter, 1990). Thus, the use of endogenous phospholipids to form vesicles as drug carriers may have much less adverse effects in patients compared to synthetic drui carrier molecules. 

Special carrier molecules exist for certain substances that are important for cell function and too large or too insoluble in lipid to diffuse passively through membranes, eg, peptides, amino acids, glucose. These carriers bring about movement by active transport or facilitated diffusion and, unlike passive diffusion, are saturable and inhibitable. Because many drugs are or resemble such naturally occurring peptides, amino acids, or sugars, they can use these carriers to cross membranes. 

Electrons from the FeS clusters of NADH dehydrogenase are passed on to ubiquinone (CoQ), a small lipid-soluble molecule in the inner mitochondrial membrane. This molecule can act as an electron carrier by accepting up to two electrons and two H+ ions. In so doing, ubiquinone (CoQ) is converted to ubiquinol (CoQH2). 

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