References: Lecithin
Gastroenterology. 1989 Mar;96(3):838-47.
Role of pancreatic enzymes and their substrates in autodigestion of the pancreas. In vitro studies with isolated rat pancreatic acini.
Nagai H, Henrich H, Wunsch PH, Fischbach W, Mossner J.
Department of Experimental Surgery, University of Wurzburg, Federal Republic of Germany.
Intrapancreatic activation of proteases is believed to play a major role in the pathogenesis of acute necrotizing pancreatitis. Several authors have questioned, however, the central role of trypsin in autodigestion of the pancreas. To clarify the direct effects of pancreatic enzymes and other related factors on acinar cells, we used the model of isolated pancreatic acini. Acini were prepared from male Wistar rats by collagenase digestion. Protein synthesis was measured by incubation of acini with [35S]methionine. Acini were resuspended thereafter in fresh buffer and further incubated for 30-90 min under various conditions [e.g., with pancreatic homogenates, ascites (from rats with pancreatitis induced by sodium taurocholate), pure pancreatic enzymes, and other factors]. The percentage of release of newly synthesized proteins into the culture medium was regarded as a biochemical parameter of cellular integrity. A morphologic score of cellular integrity was obtained via light microscopic evaluation of acini at the end of the various incubations by measuring the degree of cell lysis, loss of cell granules, ballooning, formation of vacuoles, and karyopyknosis. When normal [35S]methionine-labeled pancreatic acini were incubated with various factors, the percentage of release of labeled proteins into the medium was as follows: incubation with HEPES/Ringer's buffer, 1.8%; hemorrhagic pancreatic ascites, 3.8%; pancreatic homogenates, 2.0%; lipase, 1.8%; phospholipase A2, 3.0%; phospholipase A2 + lecithin, 3.2%; trypsin, 2.5%; 5% olive oil, 1.8%; ascites + olive oil, 78.3%; ascites + homogenized epididymal fat, 79.9%; lipase + olive oil, 32.0%; pancreatic homogenates + olive oil, 28.0%;
J Biol Chem. 1989 Feb 5;264(4):1963-7.
Human plasma lecithin-cholesterol acyltransferase. Inhibition of the phospholipase A2-like activity by sn-2-difluoroketone phosphatidylcholine analogues.
Jauhiainen M, Yuan W, Gelb MH, Dolphin PJ.
Department of Biochemistry, Lipoprotein Research Group, Dalhousie University, Halifax, Nova Scotia, Canada.
Lecithin-cholesterol acyltransferase (LCAT) is a plasma enzyme which catalyzes the transacylation of the sn-2-fatty acid of lecithin to cholesterol, forming lysolecithin and cholesteryl ester. We have recently proposed a covalent catalytic mechanism for LCAT in which lecithin cleavage proceeds via the formation of a transition state tetrahedral adduct between the oxygen atom of the catalytic serine residue and the sn-2-carbonyl carbon atom of the substrate (Jauhiainen, M., Ridgway, N.D., and Dolphin, P.J. (1987) Biochim. Biophys. Acta 918, 175-188). This proposal is evaluated here by use of nonhydrolyzable sn-2-difluoroketone phosphatidylcholine analogues, known to inhibit calcium-dependent phospholipase A2. These compounds inhibited the calcium-independent phospholipase A2 activity of LCAT in a time and concentration dependent manner. The most potent analogues had a 100-fold higher affinity for the enzyme than the substrate, lecithin, when present within lecithin/apoA-I proteoliposomes. The inhibition was dependent upon the presence of a difluoromethylene group alpha to the sn-2-carbonyl carbon of the analogues. The inhibition is attributed to the formation of a tetrahedral adduct between the catalytic serine residue of LCAT and the sn-2-carbonyl carbon atom of the analogues which is stabilized by the electronegative fluorine atoms present upon the carbon atom alpha to the carbonyl carbon. This adduct mimics that proposed by us to occur during lecithin cleavage by LCAT, and the data substantiate the existence of this transition state adduct prior to the release of lysolecithin and formation of a fatty acylserine oxyester of the enzyme.
Laxative online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=29&dopt=Abstract lecithin
Bioorg Khim. 1993 Feb;19(2):243-9.
[Study of the interaction of alpha-tocopherol with phospholipids, fatty acids, and their oxygenated derivatives by (31)P-NMR spectroscopy]
[Article in Russian]
Chudinova VV, Zakharova EI, Alekseev SM, Chupin VV, Evstigneeva RP.
Interaction of alpha-tocopherol with phospholipids, oleic, ricinoleic acids and linoleic acid hydroperoxides was investigated by means of 31P NMR spectroscopy on a model artificial membranes containing egg phosphatidylcholine and lysophosphatidylcholine. alpha-Tocopherol was shown to support the bilayer organization of lysophospholipids, whereas its introduction into the lecithin-water system stimulated the hexagonal phase formation. Free fatty acids exhibited a synergism to alpha-tocopherol, the effect of the hexagonal phase formation being at most increased by oxygenated acids--ricinoleic acid and linoleic acid hydroperoxides. In accordance with the experimental data, a conclusion about modifying and structuring action of alpha-tocopherol was made. Origin of the alpha-tocopherol's modulating effect on the membrane structure and a possible role of hexagonal phase forming upon its action in the course of peroxidation of lipids was discussed.
Laxative online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8498962&dopt=Abstract lecithin
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