Phospholipids association properties

The transport behavior of Li+ across membranes has been the focus of numerous studies, the bulk of which have concentrated upon the human erythrocyte for which the Li+ transport pathways have been elucidated and are summarized below. The movement of Li+ across cell membranes is mediated by transport systems which normally transport other ions, therefore the normal intracellular and subcellular electrolyte balance is likely to be disturbed by this extra cation. Additionally, Li+ has been shown to increase membrane phospholipid unsaturation in rat brain, leading to enhanced fluidity in the membrane, which could have repercussions for membrane-associated proteins and for membrane transport properties. 

Natural biological membranes consist of lipid bilayers, which typically comprise a complex mixture of phospholipids and sterol, along with embedded or surface associated proteins. The sterol cholesterol is an important component of animal cell membranes, which may consist of up to 50 mol% cholesterol. As cholesterol can significantly modify the bilayer physical properties, such as acyl-chain orientational order, model membranes containing cholesterol have been studied extensively. Spectroscopic and diffraction experiments reveal that cholesterol in a lipid-crystalline bilayer increases the orientational order of the lipid acyl-chains without substantially restricting the mobility of the lipid molecules. Cholesterol thickens a liquid-crystalline bilayer and increases the packing density of lipid acyl-chains in the plane of the bilayer in a way that has been referred to as a condensing effect. 

PH domains bind phosphatidyl inositol derivatives and, due to this property, are able to mediate membrane association of signal proteins. The PH domain of PL-C61 binds to phospholipids such as Ptd(Ins)P2 with high affinity and specificity. The crystal structure of the PH domain of PL-C81 with bound Ptd(Ins)P2 surprisingly has a very similar folding topology to the PTB domain that specifically binds phosphotyrosine-containing peptides (see 8.2.3 review Lemmon et al, 1996). The importance of this similarity is not understood. 

Taken together, these results showed that EGb can prevent ischemia-induced Na,K-AIPase injury, and suppress hypoxia- and ECS-induced membrane phospholipid breakdown in the brain, and bilobalide might be associated with its protective action. In addition, EGb reduces AA-induced neuronal damage as a consequence of the increase in reincorporation of AA Therefore, these mechanisms might provide a possible explanation for neuroprotective properties of EGb and bilobalide against oxidative damage. 

Lipids and phospholipids too accumulate at the site of active mineralization. It has been proposed that phosphatidylserine can combine with hydrated metal ions and form a bi-or possibly a tridentate complex417. In forming such a complex, the hydrophilic properties of Ca2+ are decreased and ligands could associate with the... 

Since its discovery, isolation, and purification in the early twentieth century, insulin has been administered to diabetic patients exclusively by injection until the recent introduction of inhaled insulin. Insulin possesses certain physiochemical properties that contribute to its limited absorption from the gastrointestinal tract, and requires subcutaneous injection to achieve clinically relevant bioavailability. With a molecular size of 5.7 kDa, insulin is a moderately sized polypeptide composed of two distinct peptide chains designated the A chain (21 amino acid residues) and the B chain (30 amino acid residues) and joined by two disulfide bonds. Like all polypeptides, insulin is a charged molecule that cannot easily penetrate the phospholipid membrane of the epithelial cells that line the nasal cavity. Furthermore, insulin monomers self-associate into hexameric units with a molecular mass greater than 30 kDa, which can further limit its passive absorption. Despite these constraints, successful delivery of insulin via the nasal route has been reported in humans and animals when an absorption enhancer was added to the formulation. 

---