Transfer vesicles

Figure 20-8 (A) Electron micrograph showing a transverse section through part of the Golgi apparatus of an early spermatid. Cistemae of the ER, Golgi stacks (S), and vesicles (V) can be seen. Curved arrows point to associated tubules. Magnification X45/000.276 Courtesy of Y. Clermont. (B) Scheme showing functions of endoplasmic reticulum, transfer vesicles, Golgi apparatus, and secretion vesicles in the metabolism of glycoproteins.

The permeability of small molecules other than water can be determined by simply transferring vesicles into a hyperosmotic solution containing the test solute. Preliminary studies transferred a vesicle (200 mOsm sucrose inside) from a glucose solution (200 mOsm) into a urea solution (240 mOsm). As shown in Figure 9.16, the vesicle volume first reduced then increased. 

The Golgi apparatus consists of a stack of membrane sacs and associated vesicles. It is an extension of the ER. Transfer vesicles transport the proteins issued from the ER to the sacs of the Golgi apparatus. The Golgi apparatus has a dual function. It is responsible for the glycosylation of protein, then sorts so as to direct them via specialized vesicles either into the vacuole or into the plasmic membrane. An N-terminal peptidic sequence determines the directing of proteins towards the vacuole. This sequence is present in the precursors of two vacuolar-orientated enzymes in the yeast Y carboxypeptidase and A proteinase. The vesicles that transport the proteins of the plasmic membrane or the secretion granules, such as those that transport the periplasmic invertase, are still the default destinations. 

ISOLATION OF TRANSFER VESICLES ISSUED FROM THE ENDOPLASMIC RETICULUM OF LEEK SEEDLINGS... 

Generation of nanoparticles under Langmuir monolayers and within LB films arose from earlier efforts to form nanoparticles within reverse micelles, microemulsions, and vesicles [89]. Semiconductor nanoparticles formed in surfactant media have been explored as photocatalytic systems [90]. One motivation for placing nanoparticles within the organic matrix of a LB film is to construct a superlattice of nanoparticles such that the optical properties of the nanoparticles associated with quantum confinement are preserved. If mono-layers of capped nanoparticles are transferred, a nanoparticle superlattice can be con-... 

The mechanisms involved in the establishment of lipid asymmetry are not well understood. The enzymes involved in the synthesis of phospholipids are located on the cytoplasmic side of microsomal membrane vesicles. Translocases (flippases) exist that transfer certain phospholipids (eg, phosphatidylcholine) from the inner to the outer leaflet. Specific proteins that preferentially bind individual phospholipids also appear to be... 

Fig. 9. Transfer of mannitol bound to inside-out vesicles to the cytoplasmic volume. (A) Unphos-phorylated ll ". (B) Phosphorylated 11 . It is assumed that the phosphoryl group transfer from the enzyme to the sugar can only take place when the sugar is bound the cytoplasmic-facing binding site, E-Pcyt Mtl (see also Fig. 6).

An attractive way to overcome this problem is to use microheterogeneous photocatalytic systems based on lipid vesicles, i.e. microscopic spherical particles formed by closed lipid or surfactant bilayer membranes (Fig. 1) across which it is possible to perform vectorial photocatalytic electron transfer (PET). This leads to generation of energy-rich one-electron reductant A" and oxidant D, separated by the membrane and, thus, unable to recombine. As a result of such PET reactions, the energy of photons is converted to the chemical energy of spatially separated one electron reductant tmd oxidant. 

The artificial lipid bilayer is often prepared via the vesicle-fusion method [8]. In the vesicle fusion process, immersing a solid substrate in a vesicle dispersion solution induces adsorption and rupture of the vesicles on the substrate, which yields a planar and continuous lipid bilayer structure (Figure 13.1) [9]. The Langmuir-Blodgett transfer process is also a useful method [10]. These artificial lipid bilayers can support various biomolecules [11-16]. However, we have to take care because some transmembrane proteins incorporated in these artificial lipid bilayers interact directly with the substrate surface due to a lack of sufficient space between the bilayer and the substrate. This alters the native properties of the proteins and prohibits free diffusion in the lipid bilayer [17[. To avoid this undesirable situation, polymer-supported bilayers [7, 18, 19] or tethered bilayers [20, 21] are used. 

Polymerization of Lipid 1 by UV Irradiation. The vesicle suspension prepared as described above was transfered into a quartz tube which was then flushed with nitrogen gas for about 20 minutes. After the tube was sealed with a rubber stopper, it was put on a rotator contained in a miniphotoreactor for UV irradiation for 3 minutes with slow rotation. 

Acetylcholine, which is set free from vesicles present in the neighbourhood of the presynaptic membrane, is transferred into the recipient cell through this channel (Fig. 6.25). Once transferred it stimulates generation of a spike at the membrane of the recipient cell. The action of acetylcholine is inhibited by the enzyme, acetylcholinesterase, which splits acetylcholine to choline and acetic acid. 

Davenport LD, Knutson JR, Brand L (1986) Excited-state proton transfer of equilenin and dihydro equilenin inreractions with bilayer vesicles. Biochemistry 25 1186-1195... 

Lukac S (1984) Thermally induced variations in polarity and microviscosity of phospholipid and surfactant vesicles monitored with a probe forming an intramolecular charge-transfer complex. J Am Chem Soc 106 4386 -392... 

Dissected adult female the parasite has been cut longitudinally and the gut and reproductive organs removed to form the characteristic muscle flap . (C) Vesicles forming from a muscle cell after treatment with collagenase the vesicles are then transferred to the experimental chamber, where vesicle-attached patches are formed and single-channel recordings made. 

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