Choline incorporation into

Me- C] choline incorporated into phosphatidylcholine of cell membranes by phosphoryl choline transferase motion of the polar headgroup is similar to that for sonicated lipid vesicles large intracellular pool of phosphoryl [Me- C] choline exists. Ti values of intracellular phosphorylcholine Indicate that intracellular viscosity -1.2 times that of water. 

Rate of choline incorporation into PC of lung slices Enzyme activities 90 64,125 ... 

Type 11 pneumocytes isolated 14 d after intratracheal instillation of 10 mg siUca to rats and plated at high density (0.5 x lOVcm ) on fibrinogen/collagen matrices in Dulbecco s modified Eagle s medium supplemented with rat serum showed an increased DNA synthesis as compared with type II pneumocytes from saline instilled controls (Baker et al. 1988). These differences had disappeared by 4d. The rates of [ C] choline incorporation into phospholipids by hypertrophic and by non-hypertrophic cells were similar after 2 and 4 d but were 150% faster than by cells from saline control rats at 2 d however, no differences in the rates of incorporation of [ H]palmitate were found between the groups. 

Me- C]Choline incorporation into phosphatidylcholines was decreased in isolated rat alveolar epithelial type II cells exposed to paraquat (5-10 ) and hyperoxia (90 % O2) (Haagsman et al. 1987). The incorporation of [1- C]acetate into phosphatidylcholines, phosphatidylglycerols and neutral lipids appeared to be very sensitive to inactivation by paraquat. The rate of [l- C]palmitate incorpora-... 

To test if some stress compounds had beneficial effects on aphids proline, choline and glycine-betaine were incorporated into artificial diets. Proline and choline appeared to decrease survival of aphids, while glycine-betaine did not (Table V). Moreover, glycine-betaine caused a drastic increase in aphid reproduction. Thus, the increased susceptibility to aphids of water stressed plants may be partially due to the higher content of glycine-betaine. 

Diethanolamine has been shown to inhibit choline uptake into cultured Syrian hamster embryo (SHE) and Chinese hamster ovary cells and to inhibit the synthesis of phosphatidylcholine in in-vitro systems in a concentration-dependent, competitive and reversible manner (Lehman-McKeeman Gamsky, 1999, 2000). Diethanolamine treatment caused a marked reduction in hepatic choline metabolite concentrations in mice following two weeks of dermal dosing. The most pronounced reduction was in the hepatic concentration of phosphocholine, the intracellular storage form of choline (Stott et al, 2000). Moreover, the pattern by which choline metabolites were altered was similar to the pattern of change that has been observed following dietary choline deprivation in rodents (Pomfret et al, 1990). Excess choline also prevented diethanolamine-induced inhibition of phosphatidylcholine synthesis and incorporation of diethanolamine into SHE cell phospholipids (Lehman-McKeeman Gamsky, 2000). 

Diethanolamine is metabolized by biosynthetic routes common to endogenous alkanolamines (ethanolamine and choline) and incorporated into phospholipids. It is excreted predominantly unchanged with a half-life of approximately one week in urine. In the absence of sodium nitrite, no conversion to TV-nitrosodiethanolamine is observed. Diethanolamine competitively inhibits the cellular uptake of choline in vitro and hepatic changes in choline homeostasis, consistent with choline deficiency, are observed in vivo. 

Another strategy to reduce toxicity and maximize biodegradability is to make use of cations and anions from Nature, which have a minimal impact on the environment. Examples include ILs based on choline [60] with counteranions such as acetate, succinate, or malate that can be readily incorporated into biochemical pathways. Choline hexanoate is not only completely biodegradable [61], but also is effective in... 

In nature, polypeptides with amphiphilic structures are known to form transmembrane channels formed by an assembly of several helices, so as to present their polar faces inward and their apolar faces outward. In view of such behavior, the photochromic amphiphilic polypeptide was incorporated into a cationic bilayer membrane composed of dipalmitoyl phosphatidyl choline.11201 Fluorescence and microscopic measurements provided evidence that the polypeptide was able to form bundles of helical molecules analogous to their natural counterparts, which acted as transmembrane channels for K+ ions. Irradiation, and the consequent transacts isomerization of the azobenzene link, caused a bending of the molecular structure and a destabilization of the transmembrane bundles. Therefore, formation of ion permeable channels would be favored or inhibited depending on whether the azo moiety... 

Having shown that dibutyryl PC is monomeric under the enzyme assay conditions, we found that the phospholipase A2, which acts poorly on PE in mixed micelles, is activated by dibutyryl PC which is itself an even poorer substrate. 31p-NMR spectroscopy was employed to show that only PE is hydrolyzed in mixtures of various compositions of these two phospholipids. The fully activated enzyme hydrolyzes PE at a similar rate to its optimal substrate, PC containing long-chain fatty acid groups. Because dibutyryl PC is not incorporated into the micelles, these results are consistent with a mechanism of direct activation of the enzyme by phosphoryl-choline-containing lipids (either monomeric or micellar) rather than a change in the properties of the interface being responsible for the activation of phospholipase A2. Therefore, two functional sites on the enzyme have to be assumed an activator site and a catalytic site (6). 

These were developed in an endeavor to expand the range of metals that could be incorporated into an ionic liquid. The presence of waters of hydration decreases the melting point of metal salts because it decreases the lattice energy. Hence, as Figure 2.4 shows, hydrated salts should be more likely to form mixtures with quaternary ammonium salts that are liquid at ambient temperature than anhydrous salts. Table 2.5 shows a list of some of the metal salts that have been made into ionic liquids with choline chloride and the freezing point of a lChCl 2metal salt mixture. 

However, in general, incorporation of the choline nitrogen into a heterocyclic ring markedly lowers the potency compared with acetylcholine (47, 48). 

Photo-responsive Synthetic Membranes. Although the visual Information transduction Is too complexed to be realized in vitro, the photoeffects of retinal-containing synthetic membranes have been investigated. Alzawa et al. (74) prepared a photo-responsive membrane from a solution of 11-cis retinal, phosphatidyl choline and trlacetyl cellulose. The retinal was assumed to be incorporated into the molecular assemblies of phosphatidyl choline, which were dispersed In the trlacetyl cellulose membrane matrix. The membrane responded to visible light by showing a transmembrane potential in association with the photoisomerization of membrane-bound 11-cis retinal. On the other hand, a membrane Incorporating 11-cls retinal without phosphatidyl choline exhibited little light-induced transmembrane potential (75). 

Such liposomes were prepared by detergent dialysis from a mixture of phosphatidyl choline and cholesterol. Antibody modified with Wglutaryl phosphatidyl ethanolamine (NGPA) (44) was incorporated into the liposomal membrane in the process of liposome preparation. PEG modified with NGPA was also... 

Chakrin and Whittaker (1969) demonstrated that intracerebrally injected or topically applied [Me-3H]choline was rapidly distributed throughout the brain and readily labelled the labile bound and, to a lesser extent, the stable bound (vesicular) ACh. Ansell and Spanner (1968) showed that intracerebrally injected [Me-1 C]-choline was also rapidly phosphorylated and incorporated into a lipid-bound form in whole brain tissue. The rapid utilization of free choline after intracerebral injection contrasts with the more recent finding of Ansell and Spanner (1971) that there is no measurable transport of free choline to the brain from the blood in vivo and that the organ may well receive its supply of choline, and hence the choline for ACh-synthesis, in a lipid-bound form from the blood. 

Lipotrophic factors are those required for transportation of triacylglycerol from the liver to the adipose tissue for storage. These factors are those that cannot be synthesized from nonlipotrophic components of the diet. The major role of lipotrophic factors is the formation of phosphatidylcholine, which is critical in VLDL formation. One of the lipotrophic factors obviously would be choline, which can be incorporated into phosphatidylcholine. Two other lipotrophic factors are related to the potential de novo synthesis of choline. The first and foremost is methionine, which can be used to donate the methyl groups for choline formation in the absence of dietary choline, thus allowing lipids to be moved from liver to adipose tissue (Fig. 18.7). 

Bile salts such as sodium cholate, taurocholate and glycocholate form micelles in solution. Long chain phosphotidyl choline may be added and the phospholipid molecules, although for geometric reasons they do not form micelles on their own, can be incorporated into the bile acid micelles. These so-called mixed micelles are relatively well tolerated when injected intravenously. They have been used to solubilize water-insoluble vitamins and other slightly soluble pharmaceuticals, such as diazepam. 

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