Transmembrane transport solutes

Many experimental variations are possible when performing uptake studies [246]. In a simple experiment for which the cells are initially free of internalised compound, the initial rates of transmembrane transport may be determined as a function of the bulk solution concentrations. In such an experiment, hydrophilic compounds, such as sugars, amino acids, nucleotides, organic bases and trace metals including Cd, Cu, Fe, Mn, and Zn [260-262] have been observed to follow a saturable uptake kinetics that is consistent with a transport process mediated by the formation and translocation of a membrane imbedded complex (cf. Pb uptake, Figure 6 Mn uptake, Figure 7a). Saturable kinetics is in contrast to what would be expected for a simple diffusion-mediated process (Section 6.1.1). Note, however, that although such observations are consistent... 

An example of a channel- or pore-forming antibiotic is gramicidin A (9.57), a peptide consisting of 15 amino acids. It induces the transmembrane transport of protons, alkali-metal ions, and thallium ions at concentrations as low as 10 ° M, even though it is unable to complex these ions in solution. Gramicidin also forms several dimers with itself. 

Kutchai HC. Cellular membranes and transmembrane transport of solutes and water. In Berne RM, Levy MN, eds. Principles of Physiology. 3rd ed. St Louis, MO CV Mosby 2000. 

Manufacture of bacterial cellulose with desired shape Development of Kedem-Katchalsky equations of the transmembrane transport for binary nonhomogeneous non-electrolyte solutions Honeycomb patterned bacterial cellulose... 

Many transmembrane transporter proteins, termed secondary transporters, use the discharge of an ionic gradient to power the uphill translocation of a solute molecule across membranes. Couphng solute movement to ion transport enables these secondary transporters to concentrate solutes by a factor of 10 with a solute flux 10 faster than by simple diffusion. We have already encountered the co-transport of leucine and Na+ by LeuT, but there are many other examples. Sugars and amino acids can be transported into cells by Na+-dependent symports. Dietary glucose is concentrated in the epithelial cells of the small intestine by a Na -dependent symport, and is then... 

Transport Properties. Important transmembrane transport parameters of the fibers are Lp, the hydraulic conductivity Pm, the diffusive permeability for a given solute o, the solute reflection coefficient and R, the solute rejection. These coefficients appear in the following equations, which are assumed to be valid at the steady state at each position Z along the fiber wall ... 

A countercurrent plate-and-frame dialyzer is to be sized to process 1.0 m3/h of an aqueous solution containing 25 wt% H2S04 and smaller amounts of copper and nickel sulfates. A wash water rate of 1000 kg/h is to be used, and it is desired to recover 60% of the acid at 298 K. From laboratory experiments with an acid-resistant vinyl membrane, a permeance of 0.03 cm/min for the acid and a water-transport number of +0.8 were reported. Transmembrane transport of copper and nickel sulfates is negligible. For these operating conditions, it has been estimated that the combined external mass-transfer coefficients will be 0.02 cm/min. Estimate the membrane area required. 

Facilitated transport proteins, such as the glucose transporter, are present in the cell membrane in limited number. As the concentration of the solute increases at the external membrane surface, the transporter binding sites become saturated, and the net rate of solute transport across the membrane approaches a maximal value (Figure 5.11). The rate of transport via the facilitated transport mechanism can be analyzed by considering binding of the transported solute (S) to the transmembrane carrier protein (Cp) to form a carrier-solute complex (S-Cp) ... 

Research of synthetic transporters selective for anions is less developed than that devoted to cation transporters. Nevertheless, in the last few years this area has received much attention. Chloride is the most abundant anion in physiological solutions and hence chloride transporters are the most studied. The transmembrane transport of other physiologically relevant anions such as bicarbonate was characterized more recently and there are examples of systems promoting phosphate and carboxylate transport. ... 

PIMs share many characteristics with polymer ion-selective electrode (ISE) membranes which have been known for many years and are often referred to as plasticized membranes (Nghiem et al, 2006). PIMs are designed for fast transport of the target chemical species across the membrane. They often completely extract a particular species from a solution, as is common with separation techniques for hydrometallurgical or remedial environmental applications (Cox, 2004 Lo et al, 1983). These properties of PIMs are in sharp contrast with those of the plasticized membranes used in ISEs where the transmembrane transport is negligible. 

Pillararenes (PA), a new kind of paracyclophane, were first synthesized in 2008 as pillar[5]arene (PA[5]) and were recognized as a new generation of supramolecular host because of their unique pillar structural feature, nanometer-sized (<1.0nm) cavity, and multiple fiinctionalizable sites. In the last few years, these new types of compound have shown biomedical applications in the construction of artificial channels for transmembrane transport of physiologically active solutes and vesicles for drug delivery, which will be reviewed in this chapter. 

The theoretical description of the kinetics of transmembrane transport through a liquid membrane should be based on the principles of solvent extraction kinetics. It should be determined by the processes at both water/membrane interphases and should also involve the intermediate step of diffusion in the membrane. Thus the existence of all these three steps makes the membrane system and its description much more complicated than the relatively simple water/organic phase. However, even the kinetics mechanism in simpler extraction systems is often based on the models dealing only with some limiting situations. As it was pointed out in the beginning of this paper, the kinetics of transmembrane transport is a fimction both of the kinetics of various chemical reactions occurring in the system and of diffusion of various species that participate in the process. The problem is that the system is not homogeneous, and concentrations of the substances at any point of the system depend on the distance from the membrane surface and are determined by both diffusion and reactions. The solution of a system of differential equations in this case can be a serious problem. 

Analysis of the first term in the equation 22 demonstrates that transmembrane transport could be induced by the diference of either or concentrations in the two solutions, i.e. concentration gradient of one ion can be used to provide an uphill transport of another ion. In biology, this type of process is well-known as secondary active transport. At equilibrium, where F=0, we have... 

Biological membranes, it should be noted, are far from homogeneous. They are usually a mixture of a variety of lipids and some smaller molecules, e.g., cholesterol, the exact composition of which is adjusted by the organism in response to environmental changes. In this context, proteins that perform membrane-based functions should truly be considered a part of the membrane, as many preserve neither their structure nor function outside of the membrane environment. Furthermore, although the biological functions performed at membranes are seemingly diverse, at some point in their action all make use of the relative impermeability of membranes. Thus, many of the proteins involved perform transmembrane transport of one type of solute or another. 

Biosorption is a process where metal ions (or metalloid species), compoimds and particulate substances are removed from solution by biological material through adsorption of the contaminant on a surface site of the biomass. It can be by physical forces (e.g. van der Waals, electrostatic interaction) and/or involving a chemical reaction. It is believed that biosorption using dead biomass is based on the physical sorption phenomenon, whereas sorption using live biomass occurs through both physical and chemical processes as well as transmembrane transport and accumulation of heavy metals in the algal cell. ... 

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