Membranes active life

Giuliani A, Pirri G, Bozzi A, Di Giulio A, Aschi M, Rinaldi AC (2008) Antimicrobial peptides natural templates for synthetic membrane-active compounds. Cell Mol Life Sci 65 2450-2460... 

Toniolo C, Crisma M, Formaggio F, Peggion C, Epand RF, Epand RM. Lipopeptaibols, a novel family of membrane active, antimicrobial peptides. Cell. Mol. Life Sci. 2001 58 1179-1188. 

The cellular membrane is a hydrophobic barrier that surrounds the cytoplasm of every cell and is involved in complex cellular processes, such as signaling and transport, which are essential to maintain the normal life cycle of a cell major components of this cellular membrane are lipids, proteins, peptides, and carbohydrates. Peptides that interact with cellular membranes are referred to as membrane-active peptides and can be broadly divided into three major classes antimicrobial, cell-penetrating, and fusogenic peptides. Any of these may have variable lengths, hydrophobicities, and secondary structures, but they often exhibit similar effects on membranes. For example, some antimicrobial peptides have cell-penetrating properties, and vice versa [23,24] these peptides usually cause some degree of membrane destabilization. 

Antibiotic-resistant bacteria cause life-threatening infections in hospitals and society in general. There is a vital requirement to develop new antimicrobial agents, but this task involves extensive scientific trials. This chapter reviewed broad-spectrum polymeric antimicrobials, which are not susceptible to current resistance, and mechanisms of bacteria to mimic the antimicrobial action of natural HDP, which exert their effect by permeabilising the bacterial cytoplasmic membrane. Most cationic antimicrobial polymers appear to work in a manner similar to membrane-active AMP, such as magainin. The design and synthesis of different polymers, such as methacrylate-based copolymers, PPE, polynorbornene by-products, amphiphilc arylamide polymers and large polymers, have been studied as biomimetic polymers in different applications. 

The key component of a membrane cell is the ion-exchange membrane, which determines the performance characteristics of the ceU, reckoned in terms of cell voltage, current efficiency, product purity, and the active life of the cell. The ion-exchange membrane operates best if it maintains its dimensional and structural integrity in the cell during startup, shutdown, and operation. It is essential that the membrane is fully stretched in the cell without any folds or wrinkles and is not subjected to physical wear or fluttering. Furthermore, the entire surface of the membrane should be exposed to a constant flux of sodium ions and water molecules during operation. 

The active life of a membrane is determined by the economic balance between membrane cost and energy cost in use [149]. 

Cross-flow filtration normally employs a surface filtration medium, since any solids moving into the thickness of the medium would not improve the efficiency of the process, and would reduce the active life of the filter medium. This medium is usually (but not always) a membrane, which is why the two topics are covered in this one chapter. (There is also considerable coverage of the membrane and related filters in Section 2F.)... 

Bopindolol is a long-acting, nonselective P-adrenoceptor blocker. It has mild membrane stabilizing activity and ISA. In vivo, the compound is hydrolyzed to its active metabohte. Because of this prodmg feature the onset of action is slower than other available P-adrenoceptor blockers. Preliminary pharmacokinetic studies indicate that the compound is weU absorbed, is 70% bioavailable, and peak plasma levels are achieved in about 2 h. Whereas its elimination half-life is 4—8 h, P-adrenoceptor blocking action (- 40%) is stiU apparent after 48 h. The dmg is being studied in hypertension, angina, and arrhythmias (43). 

The processes of electron transport and oxidative phosphorylation are membrane-associated. Bacteria are the simplest life form, and bacterial cells typically consist of a single cellular compartment surrounded by a plasma membrane and a more rigid cell wall. In such a system, the conversion of energy from NADH and [FADHg] to the energy of ATP via electron transport and oxidative phosphorylation is carried out at (and across) the plasma membrane. In eukaryotic cells, electron transport and oxidative phosphorylation are localized in mitochondria, which are also the sites of TCA cycle activity and (as we shall see in Chapter 24) fatty acid oxidation. Mammalian cells contain from 800 to 2500 mitochondria other types of cells may have as few as one or two or as many as half a million mitochondria. Human erythrocytes, whose purpose is simply to transport oxygen to tissues, contain no mitochondria at all. The typical mitochondrion is about 0.5 0.3 microns in diameter and from 0.5 micron to several microns long its overall shape is sensitive to metabolic conditions in the cell. 

The cell wall is a more rigid structure and is responsible for the form of the bacterial body. It behaves as a selectively permeable membrane and apparendy plays a fundamental role in the life activities of the cell. 

In addition, the authors suggest that all such systems must have a semi-permeable active boundary (membrane), an energy transduction apparatus and (at least) two types of functionally interdependent macromolecular components (catalysts and records). Thus, the phenomenon of life requires not only individual self-replication and self-sustaining systems, but it also requires of such individual systems the ability to develop a characteristic, evolutionary dynamic and a historical collectivist organisation. 

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