Membranes bilayer

There has been a surge of research activity in the physical chemistry of membranes, bilayers, and vesicles. In addition to the fundamental interest in cell membranes and phospholipid bilayers, there is tremendous motivation for the design of supported membrane biosensors for medical and pharmaceutical applications (see the recent review by Sackmann [64]). This subject, in particular its biochemical aspects, is too vast for full development here we will only briefly discuss some of the more physical aspects of these systems. The reader is referred to the general references and some additional reviews [65-69]. 

Evans E A 1974 Bending resistanoe and ohemioally induoed moments in membrane bilayers Biophys. J. 14 923... 

Certain proteins are found to be covalently linked to lipid molecules. For many of these proteins, covalent attachment of lipid is required for association with a membrane. The lipid moieties can insert into the membrane bilayer, effectively anchoring their linked proteins to the membrane. Some proteins with covalently linked lipid normally behave as soluble proteins others are integral... 

Membranes are composed of phospholipids and proteins. The fatty acid composition of the phospholipids in a membrane influences how it is affected by the cold. In general, as the temperature of a cell is lowered the lipids in the membrane bilayer undergo a phase transition from a liquid crystalline (fluid) state to a gel (more solid) state. The temperature at which this transition takes place is very narrow for phospholipids composed of a simple mixture of fatty acids, but is quite broad for the phospholipids in cellular membranes. It is usually implied from various methods... 

As described above, some solutes such as gases can enter the cell by diffusing down an electrochemical gradient across the membrane and do not require metabolic energy. The simple passive diffusion of a solute across the membrane is limited by the thermal agitation of that specific molecule, by the concentration gradient across the membrane, and by the solubility of that solute (the permeability coefficient. Figure 41—6) in the hydrophobic core of the membrane bilayer. Solubility is... 

Secretory proteins and proteins destined for membranes distal to the ER completely traverse the membrane bilayer and are discharged into the lumen of the ER. 7V-Glycan chains, if present, are added (Chapter 47) as these proteins traverse the irmer part of the ER membrane—a process called cotranslational glycosyla-tion. Subsequently, the proteins are found in the... 

The procedure for purification of Na,K-ATPase in membrane-bound form from the outer renal medulla of mammalian kidney offers the opportunity of exploring the structure of the Na,K-pump proteins in their native membrane environment. The protein remains embedded in the membrane bilayer throughout the purification procedure thus maintaining the asymmetric orientation of the protein in the baso-lateral membrane of the kidney cell in the purified preparation. This preparation has been particularly useful in studies of ultrastructure, protein conformation and for... 

It might be unexpected for cationic groups, e.g., protonated amino groups, to be important in translocation of cations across the membrane bilayer. Indeed, Grin-stein et al. [19] found that amino reagents (pyridoxal phosphate, trinitrobenzene sulfonate and diisothiocyanostilbene disulfonate) did not affect the Na /H ex-... 

A further partihon system based on the use of liposomes, and commercialized under the name Transil [110, 111], has shown its utiUty as a UpophiUcity measure in PBPK modeling [112]. Fluorescent-labeled liposomes, called fluorosomes, are another means of measuring the rate of penetration of small molecules into membrane bilayers [113, 120]. Similarly, a colorimetric assay amenable to HTS for evaluating membrane interactions and penetrahon has been presented [116]. The platform comprises vesicles of phospholipids and the chromahc Upid-mimehc polydiacetylene. The polymer undergoes visible concentrahon-dependent red-blue transformahons induced through interactions of the vesicles with the studied molecules. 

Melchior, D. L. A rapid emprirical method for measuring membrane bilayer entry equilibration of molecules. 

Steroids have long been used in the treatment of neurological injury. These highly lipophilic compounds have a high aflSnity for membrane bilayers. This property is key to their role in inhibition of lipid peroxidation. 

Makriyannis A, Banijamali A, Van der Schyf C, Jarrell H. The role of cannabinoid stereochemistry and absolute configuration and the orientation of A9-THC in the membrane bilayer. Structure-activity relationships of cannabinoids. In Rapaka RS, Makriyannis A, eds. Interactions of Cannabinoids with Membranes. National Institute on Drug Abuse Research Monograph 79. Rockville, MD US Department of Health and Human Services, 1987. 

JS Patton. Is the intestinal membrane bilayer freely permeable to lipophilic molecules In F Alvarado, CH van Os, eds. Ion Gradient-Coupled Transport. INSERM Symposium No. 26. Amsterdam Elsevier Science, 1986, pp 33-36. 

Glycolipids are carbohydrate-containing molecules, usually of sphingosine derivation, possessing a hydrophobic, fatty acid tail that embeds them into membrane bilayers. The hydrophilic... 

The advantage of this approach to liposome conjugation is that the linkage between the lectin complex and the membrane bilayer is noncovalent and reversible. The addition of a saccharide containing the proper sequence or sugar type recognized by the lectin breaks the binding... 

Liposomes are membrane-based supramolecular particles that consist of a number of concentric lipid membrane bilayers separated by aqueous compartments (Figure 13.15). They were developed initially as carriers for therapeutic drugs. Initially, the bilayers were almost exclusively phospholipid based. More recently, non-phospholipid-based liposomes have been developed. 

Alkyl chain heterogeneities cause cell membrane bilayers to remain in the fluid state over a broad temperature range. This permits rapid lateral diffusion of membrane lipids and proteins within the plane of the bilayer. The lateral diffusion rate for an unconstrained phospholipid in a bilayer is of the order of 1 mm2 s 1 an integral membrane protein such as rhodopsin would diffuse 40nm2 s 1. 

The fluidity of lipid bilayers permits dynamic interactions among membrane proteins. For example, the interactions of a neurotransmitter or hormone with its receptor can dissociate a transducer protein, which in turn will diffuse to interact with other effector proteins (Ch. 19). A given effector protein, such as adenylyl cyclase, may respond differently to different receptors because of mediation by different transducers. These dynamic interactions require rapid protein diffusion within the plane of the membrane bilayer. Receptor occupation can initiate extensive redistribution of membrane proteins, as exemplified by the clustering of membrane antigens consequent to binding bivalent antibodies [8]. In contrast to these examples of lateral mobility, the surface distribution of integral membrane proteins can be fixed by interactions with other proteins. Membranes may also be partitioned into local spatial domains consisting of networks... 

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