References: Lecithin
Biochemistry. 1992 Jun 2;31(21):4974-80.
Stereochemical and positional specificity of the lipase/acyltransferase produced by Aeromonas hydrophila.
Robertson DL, Hilton S, Buckley JT.
Department of Biochemistry and Microbiology, University of Victoria, British Columbia, Canada.
Aeromonas species secrete a glycerophospholipid-cholesterol acyltransferase (GCAT) which shares many properties with mammalian plasma lecithin-cholesterol acetyltransferase (LCAT). We have studied the stereochemical and positional specificity of GCAT against a variety of lipid substrates using NMR spectroscopy as well as other assay methods. The results show that both the primary and secondary acyl ester bonds of L-phosphatidylcholine can be hydrolyzed but only the sn-2 fatty acid can be transferred to cholesterol. The enzyme has an absolute requirement for the L configuration at the sn-2 position of phosphatidylcholine. The secondary ester bond of D-phosphatidylcholine cannot be hydrolyzed, and this lipid is not a substrate for acyl transfer. In contrast to the phospholipases, but similar to LCAT, the enzyme does not interact stereochemically with the phosphorus of phosphatidylcholine. In fact, the phosphorus is not required for enzyme activity, as GCAT will also hydrolyze monolayers of diglyceride, although at much lower rates.
Laxative online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1599923&dopt=Abstract lecithin
J Lipid Res. 1996 Feb;37(2):250-61.
Carotenoids in biological emulsions: solubility, surface-to-core distribution, and release from lipid droplets.
Borel P, Grolier P, Armand M, Partier A, Lafont H, Lairon D, Azais-Braesco V.
INRA, Unite Maladies Metaboliques, Centre de Recherche en Nutrition Humaine, Clermont-Ferrand, France.
Data on the physico-chemical properties of carotenoids in biological emulsions are essential to our knowledge of carotenoid metabolism. Therefore, we determined the behavior of carotenoids in phospholipid-stabilized triglyceride emulsions, a model for biological emulsions such as dietary emulsions, triglyceride-rich lipoproteins, and intracellular storage droplets. The solubility of beta-carotene (a model for apolar carotenoids, carotenes) in pure bulk triglycerides (0.112 to 0.141 wt % according to triglycerides) was significantly higher than zeaxanthin (a model for polar carotenoids, xanthophylls) (0.022 to 0.088 wt %). The solubility of both carotenoids increased when the chain-length of the triglycerides' fatty acids decreased. The amount of zeaxanthin associated with lipid droplet dramatically increased in phospholipid-triglyceride droplets as compared to the pure corresponding triglyceride droplets, whereas the amount of beta-carotene associated with lipid droplets increased only slightly beta-Carotene distributed almost exclusively in the core of triolein-lecithin-carotenoid droplets, while zeaxanthin distributed preferentially at the droplet's surface. A significant percentage (8.3%) of zeaxanthin was spontaneously transferred from lipid droplets to aqueous phase and the remaining part was transferred during triglyceride hydrolysis catalysed by pancreatic lipase, while beta-carotene absolutely required triglyceride lipolysis to be transferred to the aqueous phase. Our results show that polar and apolar carotenoids behave differently in biological emulsions. They further our understanding of the bioavailability of polar and apolar carotenoids and of their d
J Lipid Res. 1997 Sep;38(9):1822-32.
Adenovirus-mediated expression of hepatic lipase in LCAT transgenic mice.
Dugi KA, Vaisman BL, Sakai N, Knapper CL, Meyn SM, Brewer HB Jr, Santamarina-Fojo S.
Molecular Disease Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA.
In order to evaluate the coordinate role that hepatic lipase (HL) and lecithin:cholesterol acyltransferase (LCAT) play in modulating HDL particle heterogeneity and function in vivo we utilized recombinant adenovirus to express HL in control and LCAT transgenic mice. Adenovirus-mediated expression of human HL in control (n = 4, LCAT activity = 42 +/- 1 nmol/ml per h) and LCAT-tg mice (n = 4, LCAT activity = 3566 +/- 93 nmol/ml per h) resulted in post heparin HL activities of 24,358 +/- 6080 and 27,266 +/- 7985 nmol/ml per min, respectively. Overexpression of HL led to significant reductions in total cholesterol, phospholipids, and HDL cholesterol in both LCAT-tg (62, 62, and 63%, P < 0.05) and control mice (68, 63, and 78%, P < 0.01) as well as to the formation of more homogenous HDL. However, compared to control animals, the reductions in the plasma concentrations of HDL-cholesterol and apoA-I were less in LCAT-tg mice (HDL-cholesterol: -62 +/- 15% vs. -78 +/- 15%, P = 0.18; apoA-I: -36 +/- 7% vs. -76 +/- 8%, P < 0.0005). Gel filtration analysis revealed that in LCAT-tg mice the apoE-rich HDL1 was preferentially reduced by expression of HL in vivo. Compared to control mice the reduction in the apoA-I/A-II HDL in transgenic mice was significantly less indicating that a subset of HDL in LCAT transgenic mice are resistant to the action of HL. These combined data support a role for both HL and LCAT in modulating HDL heterogeneity and function, properties which may ultimately affect the ability of LCAT transgenic mouse HDL to function in the process of reverse cholesterol transport.
Laxative online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9323591&dopt=Abstract lecithin
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