References: Lecithin
Biochim Biophys Acta. 1993 Jun 24;1164(1):81-90.
Fusion activity of an amphiphilic polypeptide having acidic amino acid residues: generation of fusion activity by alpha-helix formation and charge neutralization.
Kono K, Nishii H, Takagishi T.
Department of Applied Chemistry, College of Engineering, University of Osaka Prefecture, Japan.
A sequential polypeptide, poly(Glu-Aib-Leu-Aib) (Aib represents 2-aminoisobutyric acid), was synthesized and the pH-dependence of fusogenic activity of the polypeptide was studied. The polypeptide was designed to take amphiphilic structure upon the formation of alpha-helix. Circular dichroism spectra of the polypeptide showed a negative Cotton effect with double minima, indicative of an alpha-helical conformation. The alpha-helix content was increased with lowering pH and/or increasing the ionic strength. It was found that the polypeptide induces remarkable leakage of calcein from egg-yolk phosphatidylcholine (EYPC) vesicles loaded in the inner aqueous phase with lowering pH and/or increasing ionic strength. The polypeptide caused fusion of EYPC liposomes and dipalmitoylphosphatidylcholine liposomes more strongly with decreasing pH. Moreover, two distinct increases of fusogenic activity of the polypeptide were observed near pH 6.0 and below pH 4.5. The former corresponds to the midpoint of pH-dependent change in helical content of the polypeptide and the latter the pKa of the gamma-carboxyl group of glutamic acid. These results indicate that elevation of the fusogenic activity of the polypeptide is related to the increase in two factors, alpha-helix content and hydrophobicity.
Laxative online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8518300&dopt=Abstract lecithin
J Clin Invest. 1992 Dec;90(6):2370-5.
Altered epitope expression of human interstitial fluid apolipoprotein A-I reduces its ability to activate lecithin cholesterol acyl transferase.
Wong L, Curtiss LK, Huang J, Mann CJ, Maldonado B, Roheim PS.
Louisiana State University Medical Center, Department of Physiology, New Orleans 70112-2822.
In human peripheral interstitial fluid, esterification of cholesterol by lecithin cholesterol acyltransferase (LCAT) was found to occur at a rate of only 10% of that in plasma (5.6 +/- 1.8 compared with 55.6 +/- 7.8 nmol/ml per h). Measurement of cholesterol esterification in the presence of excess reconstituted apoA-I HDL (rA-I HDL) revealed an LCAT activity in interstitial fluid of 24% of that in plasma, indicating that the low rate of esterification could not be caused by limiting mass of LCAT enzyme. When plasma was diluted to the same concentration as in interstitial fluid, the percent cholesterol esterification rate was the same as undiluted plasma and significantly higher than that of interstitial fluid. These findings led us to postulate that poor activation of LCAT in interstitial fluid may result from a change in conformation in apoA-I. To test this hypothesis, a monoclonal antibody AI-11 that inhibits apoA-I activation of LCAT was used to measure apoA-I in interstitial fluid and plasma. Antibody AI-11 recognized interstitial fluid apoA-I poorly, whereas a polyclonal antibody recognized interstitial fluid apoA-I normally. Incubation of antibody AI-11 with high density lipoprotein or rA-I HDL inhibited apoA-I activation of LCAT. We conclude that the altered conformation of apoA-I in interstitial fluid may render it a poor activator of LCAT.
Laxative online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1281832&dopt=Abstract lecithin
J Biochem Toxicol. 1995 Jun;10(3):121-8.
Inhibition of lecithin: cholesterol acyltransferase activity in human blood plasma by cigarette smoke extract and reactive aldehydes.
Chen C, Loo G.
Department of Food, Nutrition and Food Service Management, School of Human Environmental Sciences, University of North Carolina at Greensboro 27412-5001, USA.
Cigarette smoking is a risk factor for atherosclerosis. It is conceivable that reactive chemical components in cigarette smoke may adversely affect reverse cholesterol transport at the level of lecithin: cholesterol acyltransferase (LCAT) and promote atherogenesis. Hence, the effect of cigarette smoke extract (CSE) on the activity of LCAT in human plasma was studied. When incubated with plasma, CSE caused both concentration- and time-dependent losses of LCAT activity. Addition of glutathione, but not ascorbate, to plasma prevented loss of LCAT activity caused by CSE. Incubation of plasma with some reactive aldehydes known to be present in cigarette smoke also inhibited LCAT activity. Among five aldehydes tested, acrolein was the strongest inhibitor of LCAT, with complete enzyme inhibition occurring at 1 mM. Acetaldehyde was the weakest inhibitor of LCAT, with 85% enzyme inhibition at 50 mM. Hexanal, formaldehyde, and malondialdehyde completely inhibited LCAT activity at 10, 50, and 50 mM, respectively. When plasma was incubated with 1 mM acrolein in the presence of 2.5 mM glutathione or dihydrolipoic acid, 100 and 57% of LCAT activity, respectively, remained after incubation. This finding suggest that reactive aldehydes may form adducts with certain free sulfhydryl groups functioning in the active site of LCAT to inhibit enzyme activity. It is concluded that reactive aldehydes are at least partially responsible for the reduction in LCAT activity in plasma treated with CSE.
Laxative online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7473602&dopt=Abstract lecithin
Anal Biochem. 1989 May 1;178(2):301-5.
A purification method for apolipoprotein A-I and A-II.
Peitsch MC, Kress A, Lerch PG, Morgenthaler JJ, Isliker H, Heiniger HJ.
Institute of Biochemistry, University of Lausanne, Epalinges, Switzerland.
Apolipoproteins A-I and A-II were isolated from precipitates obtained by cold ethanol fractionation of human plasma. The starting material used in this report was precipitate B of the Kistler and Nitschmann method which corresponds approximately to fraction III of the Cohn and Oncley procedure. Through the use of urea, chloroform, and ethanol in appropriate concentrations, apolipoproteins A-I and A-II were isolated by a simple extraction technique avoiding time-consuming ultracentrifugation. Starting from 10 g of centrifuged precipitate B, approximately 100 mg of apolipoprotein A-I and 10 mg of apolipoprotein A-II were obtained. When incubated with normal human or rabbit plasma, both apolipoproteins were readily incorporated into high-density lipoproteins. Apolipoprotein A-I obtained by the cold ethanol method activated lecithin-cholesterol acyltransferase to the same extent as apolipoprotein A-I prepared by the classical flotation method. Apolipoprotein A-II had no such properties by itself, but was capable of potentiating lecithin-cholesterol acyltransferase activity of apolipoprotein A-I.
Laxative online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2502043&dopt=Abstract lecithin
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