Choline-containing

Dukhovich, A. F., et al. (1988). Choline-containing phospholipids as specific activators and stabilizers of firefly luciferase. Dokl. Akad. Nauk SSSR 298 1257-1260. 

There is also inside-outside (transverse) asymmetry of the phospholipids. The choline-containing phospholipids (phosphatidylcholine and sphingomyelin) are located mainly in the outer molecular layer the aminophospholipids (phosphatidylserine and phos-phatidylethanolamine) are preferentially located in the inner leaflet. Obviously, if this asymmetry is to exist at all, there must be limited transverse mobility (flip-flop) of the membrane phospholipids. In fact, phospholipids in synthetic bilayers exhibit an extraordinarily slow rate of flip-flop the half-life of the asymmetry can be measured in several weeks. However, when certain membrane proteins such as the erythrocyte protein gly-cophorin are inserted artificially into synthetic bilayers, the frequency of phospholipid flip-flop may increase as much as 100-fold. 

The choline-containing phospholipids, PC and Sph, predominate in the outer leaflet and the amino-containing phospholipids (PE and PS) in the inner leaflet. 

Choline-containing phospholipids Potassium iodide-bismuth subnitrate (phosphatidylcholine and Dragendorff reagent... 

Choline-containing lipids appear as orange-red spots in a few minutes... 

Transversely, mammalian biomembranes exhibit a general pattern for preferential localization of choline-containing phospholipids [such as phosphatidylcholine (PC) and... 

Briles, E.B. and Tomasz, A. (1973) Pneumococcal Forssman antigen. A choline-containing lipoteichoic acid. Journal of Biological Chemistry 248, 6394—6397. 

Choline-containing phospholipids Phospholipase D Choline oxidase 51... 

Choline-containing phospholipids have been determined in human serum using an IMER consisting of coimmobilized phospholipase D and choline oxidase [51]. Recently, immobilized glutamate oxidase was used to determine L-glutamic acid in culture media [52],... 

Choline is supplied to the neuron either from plasma or by metabolism of choline-containing compounds 193 A slow release of acetylcholine from neurons at rest probably occurs at all cholinergic synapses 194 The relationship between acetylcholine content in a vesicle and the quanta of acetylcholine released can only be estimated 194 Depolarization of the nerve terminal by an action potential increases the number of quanta released per unit time 194 All the acetylcholine contained within the cholinergic neuron does not behave as if in a single compartment 194... 

Choline is supplied to the neuron either from plasma or by metabolism of choline-containing compounds. The... 

The contribution of pseudocholinesterase, also known simply as cholinesterase, to drug metabolism is much greater as it possesses considerably broader substrate selectivity. In addition to acetylcholine, it will hydrolyze other choline esters like the muscle relaxant succinylcholine. It will also hydrolyze non-choline-containing drugs like the local anesthetic procaine and the anti-inflammatory agent aspirin (Fig. 6.5). Cholinesterases, particularly... 

Dragendorff stain A. Potassium iodide 400 g l l in water. B. Bismuth subnitrate 17 g l-1 in 20% acetic acid. Mix A and B and water (1 4 15) immediately before use Choline containing Orange-red spots within a few minutes with gentle warming... 

It can be seen from Figure 1 that the choline-containing phospholipids, phosphatidylcholine and sphingomyelin are localized predominantly in the outer monolayer of the plasma membrane. The aminophospholipids, conprising phosphatidylethanolamine and phosphatidylserine, by contrast, are enriched in the cytoplasmic leaflet of the membrane (Bretcher, 1972b Rothman and Lenard, 1977 Op den Kamp, 1979). The transmembrane distribution of the minor membrane lipid components has been determined by reaction with lipid-specific antibodies (Gascard et al, 1991) and lipid hydrolases (Biitikofer et al, 1990). Such studies have shown that phosphatidic acid, phosphatidylinositol and phosphatidylinositol-4,5-fc -phosphate all resemble phosphatidylethanolamine in that about 80% of the phospholipids are localized in the cytoplasmic leaflet of the membrane. 

The majority of PC is synthesized in mammalian cells by the CDP-choline or Kennedy pathway in the endoplasmic reticulum (Eigiue 1). In this pathway, choline taken up from the external medium or released in the cytosol by breakdown of choline containing compoimds, is first converted to phosphocholine by the enzyme choline kinase (CK) (Ishidate, 1997). There are two isoforms of CK cloned which both can convert also ethanolamine to phosphoethanolamine, albeit with a lesser affinity (Aoyama et al 2000). Alternatively phosphocholine can be generated by enzymes that preferentially phosphorylate ethanolamine and are therefore designated ethanolamine kinases (EK). As yet also two different EKs are known (EKI 1 and 2 Lykidis etal., 2001). 

In mice, diethanolamine alters choline homeostasis in a manner resembling choline deficiency. Stott et al. (2000) showed that diethanolamine induced choline deficiency and depleted several choline-containing compounds in B6C3Fi mice, while Lehman-McKeeman Gamsky (1999, 2000) found that diethanolamine inhibited the uptake of choline into mammalian cells. 

J. L. Griffin, C. J. Mann, J. Scott, . C. Shoulders and J. K. Nicholson, Choline containing metabolites during cell transfection an insight into magnetic resonance spectroscopy detectable changes, FEBS Lett., 2001, 509, 263-266. 

Hypoxic or ischemic conditions led to an immediate release of free choline via the breakdown of choline-containing phospholipids in rat hippocampus slices. Klein et d. [198] showed that bilobalide inhibited the hypoxia-induced choline release in a dose-dependent manner both in vitro (EC,0 0.38 /rM) and ex vivo (2-20 mg/kg, p.o.). Asimilar reduction of choline release was confirmed after administration of EGb (200 mg/kg, p.o.). Bilobalide also inhibits die //-methyl-D-aspartate-induced, P LA,-dependent release of choline from hippocampal phospholipids both in vitro (10-100/rM) and in vivo (20 mg/kg, ip.) [199]. 

Plasma membrane lipids are asymmetrically distributed between the two monolayers of the bilayer, although the asymmetry, unlike that of membrane proteins, is not absolute. In the plasma membrane of the erythrocyte, for example, choline-containing lipids (phosphatidylcholine and sphingomyelin) are typically found in the outer (extracellular or exoplasmic) leaflet (Fig. 11-5), whereas phosphatidylserine, phosphatidyl-ethanolamine, and the phosphatidylinositols are much more common in the inner (cytoplasmic) leaflet. Changes in the distribution of lipids between plasma membrane leaflets have biological consequences. For example, only when the phosphatidylserine in the plasma membrane moves into the outer leaflet is a platelet able to play its role in formation of a blood clot. For many other cells types, phosphatidylserine exposure on the outer surface marks a cell for destruction by programmed cell death. 

M Wada, K Nakashima, N Kuroda, S Akiyama, K Imai. Sensitive flow-injection method with peroxy-oxalate chemiluminescence detection combined with preparative high performance hquid chromatography for determination of choline-containing phospholipids in human serum. J Chromatogr B 678 129-136, 1996. 

Figure 8.7. Fluorescence micrographs of a monolayer of L-a-dipalmitoyl phosphatidyl choline containing about 1% molar of an NBD dye at a temperature of 17°C and at pH 5.5. (Reproduced from Florsheimer, M. and Mdhwald, H. 1989 Chem. Phys. Lipids 49 231-41 by kind permission of the publishers and authors.)...

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). 

The nomenclature rules just cited for phosphatidylcholine and its analogs also hold for ethanolamine phosphoglycerides. Mixtures of the diacyl, alkenyl acyl, and alkyl ether forms are found, for example, in macrophages and neutrophils but in much different ratios than observed for the choline-containing types (Figure 1-11). Again, only the (diacyl) phosphatidylethanol-amine is found in liver cells. These structures will be discussed in more detail in Chapter 5. 

Solvent I (chloroform-methanol 1 1, v/v). In 10 column volumes, all of the choline-containing phospholipids should have passed through. Then, start the following ... 

Solvent II (ethanol-chloroform-water, 5 2 2, v/v). This will elute the remaining non-choline-containing phospholipids again in approximately 10 column volumes of solvent. 

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