Macromolecular Transport

The structure of these gel-like systems of micelles is very different from that of conventional electrophoresis media made from chemically and physically cross-linked polymers of polyacrylamide and agarose [75], The absence of chemical or physical cross-links in the Pluronic gel-like phases may allow a larger degree of freedom for macromolecular transport around the obstacles that make up the medium than occurs in conventional electrophoresis media. 

Electric-field-driven transport in media made of hydrophilic polymers with nanometer-size pores is of much current interest for applications in separation processes. Recent advances in the synthesis of novel media, in experimental methods to study electrophoresis, and in theoretical methodology to study electrophoretic transport lead to the possibility for improvement of our understanding of the fundamentals of macromolecular transport in gels and gel-like media and to the development of new materials and applications for electric-field-driven macromolecular transport. Specific conclusions concerning electrodiffusive transport in polymer hydrogels include the following. 

Chapter 15 gives an extensive and detailed review of theoretical and practical aspects of macromolecular transport in nanostructured media. Chapter 16 examines the change in transport properties of electrolytes confmed in nanostructures, such as pores of membranes. The confinment effect is also analyzed by molecular dynamic simulation. 

There is growing evidence implicating Na+-dependent solute transporters and intracellular as well as extracellular Ca2+ in the physiological regulation of the paracellular pathway [81,203,204], Such modulation of paracellular permeability is especially important for drugs such as peptides and oligonucleotides that exhibit poor permeability characteristics across both the cornea and the conjunctiva [150,152,154,155], In addition, ion transporters such as Cl and Ca2+ channels have been implicated in macromolecular transport (see Sections IV.B.2 and IV.B.4). In the following discussion, some key ion transport processes and their possible roles in solute transport across epithelial tissues are summarized. 

PE Grimshaw, AJ Grodzinsky, ML Yarmush, DM Yarmush. Selective augmentation of macromolecular transport in gels by electrodiffusion and electrokinetics. Chem Eng Sci 45 2917-2929, 1990. 

The rate of sedimentation is defined by the sedimentation constant 5, which is directly proportional to the polymer mass m, solution density p, and specific volume of the polymer V, and inversely proportional to the square of the angular velocity of rotation o), the distance from the center of rotation to the point of observation in the cell r, and the fractional coefficient /, which is inversely related to the diffusion coefficient D extrapolated to infinite dilution. These relationships are shown in the following equations in which (1 — Vp) is called the buoyancy factor since it determines the direction of macromolecular transport in the cell. 

Macromolecular transport in transient polymeric networks and an introduction to the observation of rapid migration in such systems. 

Thum, A.L. (1982) Effects of endothelial injury on macromolecular transport in the arterial wall. Ph.D. Thesis. Columbia University, New York. 

D. J. Keljo, and J. R. Hamilton, Quantitative determination of macromolecular transport rate across intestinal Peyer s patches, Am. J. Physiol. 244 0631 (1983). 

Enfield CG, Bengtsson G. 1988. Macromolecular transport of hydrophobic contaminants in aqueous environments. Groundwater 26 64-70. 

It is clear that macromolecule-drug conjugates or, more accurately, macromolecular prodrugs may well alter the pharmacological and immunological activity of the parent compound. The macromolecular transport vector may vary considerably in size, electrical charges, hydrophobicity and hydrophilicity, and its ability to act as a substrate for transmembrane transport mechanisms. 

Wangensteen D. Microstmctural aspects of macromolecular transport across pulmonary epithelia. In Proceedings of the Second International Symposium on Respiratory Dmg Delivery (in press). 

Ions, small metabolites, and globular proteins up to 60 kDa can diffuse through a water-filled channel in the nuclear pore complex these channels behave as if they are -0.9 nm in diameter. However, large proteins and ribonucleoprotein complexes cannot diffuse in and out of the nucleus. Rather, these macromolecules are selectively transported in and out of the nucleus with the assistance of soluble transporter proteins that bind macromolecules and also Interact with certain nucleoporlns. The principles underlying macromolecular transport through nuclear pore complexes were first determined for the Import of individual proteins into the nucleus, which we discuss first before turning to the question of how fully processed mRNAs are transported into the c rt oplasm. 

The supply of cells with cholesterol via receptor-mediated endocytosis of LDL is one of the best characterized processes of macromolecular transport across the plasma membrane of eukaryotic cells. The following sections describe this process, provide an overview of the biochemical and physiological properties of the LDL receptor, and discuss the molecular basis for the genetic disease, familial hypercholesterolemia (FH). 

Akey, C. W. (1992). The nuclear pore complex. A macromolecular transporter. In Nuclear Trafficking (C. M. Feldherr, ed.), pp. 31-70. Academic Press, San Diego, CA. 

Research in macromolecular transport using Brownian dynamics is fundamental in that either a parameterized class of fluid flow conditions is considered or a particular experiment is modeled with well-known geometric and fluid conditions. 

Weinbaum, S., Tzeghai, G., Ganatos, P. et al. (1985) Effect of cell turnover and leaky junctions on arterial macromolecular transport. Am. J. Physiol., 248, H945-H960. 

Walker, W. A., 1979, Gastrointestinal host defense Importance of gut closure in control of macromolecular transport, in Development of Mammalian Absorptive Processes, Ciba Foundation Symposium No. 70, Excerpta Medica, Amsterdam, pp. 201-216. 

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