Polarity vesicular

Addition of cholesterol leads to two counteracting effects on the rate constants. The first is a smaller counterion binding, reducing the rate constants. The other is a rate enhancing effect resulting from the less polar vesicular binding sides. The overall effect depends on the exact reaction conditions. ... 

VESICULAR AGGREGATES AS NOVEL MEDIA FOR THE ISOLATION OF POLAR AND NON-POLAR ORGANIC COMPOUNDS PRIOR TO LIQUID CHROMATOGRAPHY... 

How the Golgi apparatus maintains its polarized structure while molecules move from one compartment to another is still a matter of debate. Two models were originally proposed based on different experimental evidence (Fig. 9-5) the vesicular transport model and the cisternal maturation model. A third model known as the dual transport model combines elements from both vesicular transport and cisternal maturation models and can better explain intra-Golgi transport. 

Liposomes, as carriers for diagnostic or therapeutic drugs, have been the focus of extensive studies over the past decades. Liposomes are vesicular particles that are composed of a membrane formed out of lipids with a polar head group and one or preferentially two long non-polar side-chains (Figs. 3,4). Typical lipids... 

Most of the characteristics invoked to explain rate accelerations and rate retardations by micelles are valid for vesicles as well. For example, the alkaline hydrolysis of A-methyl-A-nitroso-p-toluenesulfonamide is accelerated by cationic vesicles (dioctade-cyldimethylammonium chloride). This rate acceleration is the result of a higher local OH concentration which more than compensates for the decreased polarity of the vesicular pseudophase (compared to both water and micelles) resulting in a lower local second-order rate constant. Similar to effects found for micelles, the partial dehydration of OH and the lower local polarity are considered to contribute significantly to the catalysis of the Kemp elimination " by DODAB vesicles. Even the different... 

It is tempting to speculate about the reasons for the observation that surfactant aggregates often do not appear to be as effective as hoped. In the author s opinion, the reasons for this could well be (1) the choice of reactions and (2) the way in which reaction rates are compared. Starting with the first point, it appears as if micellar and vesicular catalysis is often studied for reactions for which water is intrinsically a good solvent, that is, a better solvent than less polar organic solvents. By using the less polar pseudophase formed by surfactant aggregates as a base for catalysis, part of... 

At low MEGA-n concentration, the II1/1 ratio is low (= 0.84) and almost constant suggesting that pyrene molecules reside in a rather polar environment, which is however not so polar as in an aqueous phase (III/I = 0.63). It may be considered that the very cohesive nature of the vesicular bilayer does not allow pyrene molecules to penetrate deep into the hydrophobic part, and they stay in peripheral solubilization sites. 

The process of development of a mosaic texture was observed by Taylor (2) first in thermally metamorphosed coals and then in partially carbonized vitrinite. He noted the appearance of spherical bodies in the plastic vitrinite, their growth, and the final development of the mosaic texture which is characteristic of the walls of the vesicular coke structure. From their appearance and behavior in polarized light it was deduced that the spherical bodies probably had a single plane of preferred orientation—i.e., a lamellar structure. 

Large viruses of 80 -100 nm diameter bearing 8-10 spikes at the vertices of the icosahedra cause influen-za 509,510 mumps, measles, and related diseases. The internal structure must be complex. Only 1% of the virus is RNA, and that consists of several relatively small pieces. These are negative strand viruses whose RNA is of the opposite polarity to the mRNA. The latter must be formed by transcription from the negative strand. The viruses carry their own RNA polymerase for this purpose. Of even more complex structure are the bullet-shaped rhabdoviruses which cause rabies and vesicular stomatitis.511 The diameter of these viruses is 65-90 nm and the length 120-500... 

Muday GK, Peer WA, Murphy AS. 2003. Vesicular cycling mechanisms that control auxin transport polarity. Trends Plant Sci 8 301-304. 

Figure 7 Plot of the change in the product of the coupling and maximum saturation factors as a function of macromolecular structure. At lower pH values, the spin-labelled lipids are present as vesicles and vesicular aggregates, while at higher pH values, micelles are formed. The higher psmax values for the micelles imply greater water accessibility to the radical site. The solid circles represent 16-DS (16-doxyl stearic acid, spin-labelled at the end of the lipid tail) while the open circles represent 5-DS (5-doxyl stearic acid, spin-labelled near the polar head group). Reproduced with permission from Ref. [70].

Neuropathology of Alzheimer s is also defined by accumulation of another form of insoluble protein, the neurofibrillary tangles (NFTs). NFTs are fibrillar structures largely composed of tau, a microtubule-binding protein that stabilises the microtubule tracts necessary for vesicular trafficking, endo- and exocytosis and axonal polarity. No tau mutations have yet been identified... 

As a single-cell organism, a yeast cell is not polar in an organ sense, apical versus basolateral, for example, as is the case of intestinal epithelial cells. As a free-living organism, yeast accumulates nutrients for future use in times of nutrient depletion. Thus, little copper or iron is secreted from the yeast cell. On the other hand, yeast must have a mechanism to mobilize and use stored nutrients. Iron is stored in Sa. cerevisiae in a vesicular compartment, perhaps a (the) vacuole, most likely as an Fe(III) polyphosphate (Raguzzi et al., 1988). This iron phosphate is probably not significandy different... 

In addition to the equilibrium phase structures mentioned above, non-equilibrium surfactant phase structures exist thatare also finding applications in drug delivery. Vesicular forms of surfactants are generally formed by dispersing lamellar phases in an excess of water (or non-aqueous polar solvents such as ethylene glycol or dimethylformamide) or, in the case of reversed vesicles, in an excess of oil. With most surfactants, vesicles are non-equilibrium structures that will eventually re-equilibrate back into the lamellar phases from which they originated. Vesicles are structural analogs of liposomes (discussed later) they are approximately spherical structures and have the ability... 

In the MLM and BLM vesicles, the cmc is small (< 10 M). In MLMs, the solubility of the individual monomers may be relatively large, if they contain charged head groups. Once the bolaamphiphiles are entrapped in a vesicular assembly they cannot escape, as the polar head group would have to pass through an apolar membrane, which is an unlikely process. At pH = 9, for example, the diacetic acid la dissolves reasonably well as the dianion in water. 

Figure 4,13 Aqueous dispersions of vesicles embrace one large bulk volume of water (region 1) and 8 vesicular regions with different spatial relationships to region 1 and different polarities. See text.

Spherical micelles and vesicles are formed from amphiphiles and bolaamphi-philes by the solvophobic effect and are protected against crystallization by head group repulsion. What happens if the head groups carry secondary amide groups which have an inborn and irresistible drive to form linear hydrogen bond chains in polar and apolar environments (see section 5.4) Chains will be formed, of course. The usual result will be vesicular tubules, as in the case of amphiphiles with a low cmc (typically < 10 M) and thinner micellar rods in the case of amphiphiles with a relatively high cmc (typically 10 -10" M). 

Such direct basolateral-apical sorting has been investigated in cultured Madin-Darby canine kidney (MDCK) cells, a line of cultured polarized epithelial cells (see Figure 6-6). In MDCK cells infected with the influenza virus, progeny viruses bud only from the apical membrane, whereas in cells infected with vesicular stomatitis virus (VSV), progeny viruses bud only from the basolateral membrane. This difference occurs because the HA glycoprotein of influenza... 

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