Transporter molecular properties

Scheiner-Bobis G (2002) The sodium pump. Its molecular properties and mechanics of ion transport. Eur J Biochem. 269 2424—2433... 

The distribution of the ionic species is determined by the molecular properties of the compound, but also by the nature and the concentration of the counterions present in the media [78]. For example, the influence of [Na ] on the transport kinehcs of warfarin through an octanol membrane has been reported [79]. 

The intent of this chapter is to establish a comprehensive framework in which the physicochemical properties of permeant molecules, hydrodynamic factors, and mass transport barrier properties of the transcellular and paracellular routes comprising the cell monolayer and the microporous filter support are quantitatively and mechanistically interrelated. We specifically define and quantify the biophysical properties of the paracellular route with the aid of selective hydrophilic permeants that vary in molecular size and charge (neutral, cationic, anionic, and zwitterionic). Further, the quantitative interrelationships of pH, pKa, partition... 

There are two pathways by which a drug molecule can cross the epithelial cell the transcellular pathway, which requires the drug to permeate the cell membranes, and the paracellular pathway, in which diffusion occurs through water-filled pores of the tight junctions between the cells. Both the passive and the active transport processes may contribute to the permeability of drugs via the transcellular pathway. These transport pathways are distinctly different, and the molecular properties that influence drug transport by these routes are also different (Fig. 

The thermodynamic solubility of a drug is the concentration of the compound that is dissolved in aqueous solution in equilibrium with the undissolved amount, when measured at 25°C after an appropriate time period. Aqueous solubility has long been recognized as a key molecular property in pharmaceutical science. Drug delivery, transport and distribution phenomena depend on solubility thus, it is of considerable value to possess information of the solubility value of a drug candidate, to be able to predict the solubility for unknown compounds and, finally, to be able to modify the structure of a compound in order to modulate its solubility value in an appropriate manner. 

Kinesins mediate anterograde transport in a variety of organisms and tissues. Since its discovery, much has been learned about the biochemical, pharmacological and molecular properties of kinesin [44, 45], Kinesin is the most abundant member of the kinesin family in vertebrates and is widely distributed in neuronal and nonneuronal cells. The holoenzyme is a heterotetramer comprising two heavy chains (115-130 kDa) and two light... 

The last term on the right-hand side is unclosed and represents scalar transport due to velocity fluctuations. The turbulent scalar flux ( , varies on length scales on the order of the turbulence integral scales Lu, and hence is independent of molecular properties (i.e., v and T).17 In a CFD calculation, this implies that the grid size needed to resolve (4.70) must be proportional to the integral scale, and not the Batchelor scale as required in DNS. In this section, we look at two types of models for the scalar flux. The first is an extension of turbulent-viscosity-based models to describe the scalar field, while the second is a second-order model that is used in conjunction with Reynolds-stress models. 

It is tempting to speculate that the next comprehensive examination of hemopexin-mediated heme transport will have exciting new sections devoted to the molecular properties of MHBP and the hemopexin receptor, to the mechanism of heme release from hemopexin, to new intracellular heme transport partners, and to the links provided by the hemopexin system among heme, iron, and copper at the cellular level. 

The storage of information in the ligand may allow control over the stability, selectivity, reactivity, and transport (carrier) properties of the complex. The following molecular and environmental features may serve for storing chemical information. 

The present approach to the prediction of thermal transport in turbulent flow neglects the effect of thermal flux and temperature distribution upon the relationship of thermal to momentum transport. The influence of the temperature variation upon the important molecular properties of the fluid in both momentum and thermal transport may be taken into account without difficulty if such refinement is necessary. 

Such expressions can be extended to permit the evaluation of the distribution of concentration throughout laminar flows. Variations in concentration at constant temperature often result in significant variation in viscosity as a function of position in the stream. Thus it is necessary to solve the basic expressions for viscous flow (LI) and to determine the velocity as a function of the spatial coordinates of the system. In the case of small variation in concentration throughout the system it is often convenient and satisfactory to neglect the effect of material transport upon the molecular properties of the phase. Under these circumstances the analysis of boundary layer as reviewed by Schlichting (S4) can be used to evaluate the velocity as a function of position in nonuniform boundary flows. Such analyses permit the determination of material transport from spheres, cylinders, and other objects where the local flow is nonuniform. In such situations it is not practical at the present state of knowledge to take into account the influence of variation in the level of turbulence in the main stream. 

This chapter deals with macro-, meso-, and molecular-level thermodynamic and transport hydrate properties of natural gas and condensate components, with and without solute. The feasibility of using these tools to measure the kinetics of hydrate formation and decomposition are also briefly discussed, while the results of these measurements have been discussed in Chapter 3. The results for insoluble substances such as porous media are discussed in Chapter 7. 

In most sensing situations, the analyte molecules are transported to and from the sensor by diffusion. This is particularly true for sensors in which the analyte is chemically transformed, such as sensors that rely on catalysis or in amperometric sensors. Diffusion is another activated (see (B.5)) process in which time and temperature have to be considered. It is driven by the gradient of chemical potential (A. 19). Two kinds of diffusion are most relevant. These are the Fickian diffusion, which depends on molecular properties of both the diffusing medium and of the diffusing species, and the Knudsen diffusion which depends on the size of the vessel. 

Schmitt KC, Zhen J, Kharkar P, Mishra M, Chen N, DuttaAK, Reith MEA (2008) Interactions of cocaine-, benztropine-, and GBR 12909-like compounds with wild-type and mutant human dopamine transporters molecular features that differentially determine antagonist-binding properties. JNeurochem 107 928-940... 

Frelin, C., Vigne, P., Barbry, P Lazdunski, M. (1987). Molecular properties of amiloride action and of its Na+ transporting targets. Kidney Int. 32,785-793. 

It is evident from the above discussion that the threshold voltage, current density, power efficiency, luminous efficiency and, to some extent, device lifetime of OLEDs using organic low-molar-mass compounds, oligomers and polymers depends on intrinsic molecular properties, such as HOMO and LUMO energy levels, efficiency of hole and electron injection and subsequent transport, efficiency of singlet formation and fluorescence efficiency. The... 

NADH dehydrogenase and, 189 ubiquinone reductase and, 178,182,183 Cholesterol, side chain cleavage, 83, 84-85 Choline, oxidation to betaine, 260 Choline dehydrogenase electron transport system and, 261-263 properties, 260-201 Chromatium sulfate reduction by, 281 transhydrogenase of, 54 function of, 80 molecular properties, 58, 69 purification, 55, 56 Chromium... 

Molecules are complex entities that can be numerically described in many different ways. The molecular interaction fields (MIF) represent a very particular molecular property the ability of a molecule to establish energetically favorable interactions with other molecules. For this reason, MIF have been widely used in the field of drug discovery and development, since most biological properties of a compound depend on its ability to bind different kinds of biomolecules, such as transporters, receptors and enzymes. 

Absorption of a photon by the purple iill-trans retinal chro-mophore (with a single broad absorption band with a maximum at 568 nm) initiates the reaction sequence BR-/zv K L Ml M2 N -o- N - O BR (7, 8), where each state and substate is well defined by spectroscopic and crystallographic means. Although a kinetic scheme that rigorously fits all data into a linear sequence has not yet been produced, the proton transport mechanism can be understood by the molecular properties of the intermediate states and by their interconversions. 

This description is particularly useful because the diffusion (6) coefficient is reasonably well defined in aqueous solutions, it is related to molecular properties in aqueous solutions, and it can be predicted. However, in biologic systems, the observed length X—for a single transport step—will be widely unchanged. Preferably, steady state and sink conditions are studied, which simplifies the Pick law and focuses on permeability as stated above. 

---