Polyfunctional membranes

The modem era of biochemistry and molecular biology has been shaped not least by the isolation and characterization of individual molecules. Recently, however, more and more polyfunctional macromolecular complexes are being discovered, including nonrandomly codistributed membrane-bound proteins [41], These are made up of several individual proteins, which can assemble spontaneously, possibly in the presence of a lipid membrane or an element of the cytoskeleton [42] which are themselves supramolecular complexes. Some of these complexes, e.g. snail haemocyanin [4o], are merely assembled from a very large number of identical subunits vimses are much larger and more elaborate and we are still some way from understanding the processes controlling the assembly of the wonderfully intricate and beautiful stmctures responsible for the iridescent colours of butterflies and moths [44]. 

In conclusion, it should be noted that PolyPs are polyfunctional compounds. Their most important functions are as follows phosphate and energy reservation, sequestration and storage of cations, formation of membrane channels, participation in phosphate transport, involvement in cell-envelope formation and function, gene activity control, regulation of enzyme activities, and, as a result, an important role in stress response and stationary-phase adaptation. 

In addition to multivalent interactions, the term polyvalency is used, especially if polyfunctional ligands bind to receptors on interfaces like cell membranes, which offer a large number (n 10) of two-dimensionally distributed binding sites, such as extended biological surfaces (e.g., bacteria, cells, viruses) [7,8]. 

In all animal and yeast systems, fatty acid synthesis is catalyzed by a polyfunctional hetero- (yeast) or homodimer (animal) which is localized in the cytosol of the cell (Stoops and Wakil, 1980). The introduction of the single A9 double bond with a cis configuration occurs on the preformed hydrocarbon chain, and is catalyzed by a membrane-bound stearoyl-CoA desaturase that requires in addition a reductant (two electrons) and molecular oxygen ... 

Owing to observations on certain competitive and reciprocal antiport relations between sugar and amino acid transport, Alvarado and Crane and Alvarado have recently postulated a new polyfunctional, mobile carrier system. involved in the uphill transport of sugars, neutral amino acids and basic amino acids in the small intestine that consists of a mosaic of fixed, specific membrane sites which acquire mobility as a result of deformations of the mobile membrane resulting in local, transient engagements of the two protein surfaces, thus allowing bound substrates to be alternately exposed to the extra- and intercellular fluids. ... 

In prokaryotic cells fatty acid synthesis occurs in the cytosolic compartment. However, it has been observed that ACP in E. coli appears to be somewhat loosely associated with the inner face of the plasma membrane of the cell (van den Bosch et al., 1970). Nevertheless, all the activities associated with the synthesis of palmitic acid from acetyl-CoA can be readily separated and assigned to individual proteins which have been purified and their molecular and kinetic characteristics examined in considerable detail (Vagelos, 1974). In yeast and animal cells, the fatty acid synthetase responsible for the formation of palmitic acid is always associated with the cytosolic compartment as a dimer of a polyfunctional polypeptide (ibid.). 

Identification of the functions of proteins and other polymeric complexes or cell proteomes, in which the achievements of proteomics contributes greatly, is the subject of intensive research [1], Modem technology now allows us to investigate not only individual protein molecules in living cell, but also to understand their interaction with other macromolecules and reveal their previously unknown functions. Several facts are determined participation of polyfunctional macromolecular protein complexes in the biosynthesis of fatty acids, involvement of erythrocyte membrane proteins macromolecular complexes in exchange of COJO, biological effects of some growth factors (polyfunctional proteins), which sometimes is achieved by interactions of other protein complexes, etc. [2-4],... 

Commercial interest in polyol surfactants derived from glucose exists for several reasons (1) glucose is an inexpensive agriculture-based (and therefore renewable) raw material (2) surfactants derived from glucose have a green environmental image (and are, in fact, readily degraded in the environment [1]), and (3) their polyfunctional (yet readily accessible) molecular structures offer the possibility of distinctive performance and properties relative to presently used surfactants [2], Short-chain polyol surfactants readily solubilize membrane polar lipids, and facilitate the isolation and study of membrane-bound proteins [3,4]. 

To improve proton transport of PFSA membranes at high temperatures and in order to operate PFSA membranes at temperatures above 100°C, inorganic compounds such as Si02 and Ti02 were employed as additives to retain water in the Naflon membranes for an acceptable proton conductivity. Proton conductors such as zirconium phosphate, heteropolyacid/ and heterocycle compounds including imidazole,benzimidazole, triazole, and polyfunctional phosphonic acid were also added in the Naflon membrane. In addition, ionic liquids were applied to fabricate composite Naflon membranes due to their anhydrous high conductivity and good thermal stability. Besides, Naflon/Naflon-functionalized multiwalled carbon nanotube composite membrane exhibits a remarkable improvement in proton conductivity compared to the pristine Naflon membrane. ... 

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