References: Lecithin
Gen Physiol Biophys. 1989 Jun;8(3):223-32.
Amphiphilic derivatives of betaine esters as modifiers of macrovesicular BLM.
Kuczera J, Janas T, Fogt A, Witek S, Schara M, Sentjurc M.
Department of Physics and Biophysics, Agricultural University of Wroclaw, Poland.
A series of amphiphilic derivatives of betaine esters (V-n), with the chemical structure (CH3)3N+COOCnH2n + 1Cl- (n = 10, 12, 14 or 16) were studied with respect to their effects on the electrical properties of lecithin macrovesicular membranes. Normalized resistance and breakdown voltage were found to depend on the V-n concentration in the membrane and on the alkyl chain length (n). Resistance decreases up to about 10(4) ohm.cm2 and breakdown voltage decreases by 111 mV were detected in the V-n: lecithin molar ratio range measured (0.005-0.05). Maximal decrease in breakdown voltage was observed for V-14. These findings together with the featured anionic selectivity suggest that, due to the interaction of V-n with phospholipids, hydrophilic pores are formed in the lipid bilayers. This assumption is supported by the results obtained by electron paramagnetic resonance (EPR) measurements which showed no collective changes in bilayer dynamics or ordering. In particular, rotational correlation times and order parameters of the spin probe molecules dissolved in the membrane did not change in the concentration range tested. Since a large number of defects in the membrane can be expected to influence the collective ordering and dynamics, this observation also suggest that the number of pores formed is small.
Laxative online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2548915&dopt=Abstract lecithin
J Lipid Res. 1994 Jul;35(7):1187-99.
Dissociation of lipid-free apolipoprotein A-I from high density lipoproteins.
Liang HQ, Rye KA, Barter PJ.
Department of Medicine, University of Adelaide, Australia.
Conditions under which apolipoprotein (apo) A-I dissociates from human high density lipoproteins (HDL) during incubation in vitro have been investigated. Dissociation of apoA-I was demonstrated by non-denaturing gradient gel electrophoresis followed by immunoblotting for apoA-I and by size-exclusion chromatography. It was quantitated after ultracentrifugation as the loss of apoA-I from the fraction of d < 1.25 g/ml. ApoA-I did not dissociate from HDL when they were incubated alone at 37 degrees C for up to 24 h. Nor was there dissociation of apoA-I when the HDL were incubated either with the cholesteryl ester transfer protein (CETP) in the absence of other lipoprotein fractions or with other lipoproteins in the absence of CETP. However, when mixtures of HDL and CETP were incubated for 24 h in the presence of physiological concentrations of either very low density lipoproteins (VLDL) or low density lipoproteins (LDL), there was a dissociation of up to 36% of the apoA-I from the HDL fraction that was linear with time. The dissociation of apoA-I coincided with a time-dependent reduction in HDL particle size. The percentage of apoA-I that dissociated from HDL correlated positively with the concentrations of VLDL, LDL, and CETP in the incubation but negatively with the concentration of HDL. When lecithin:cholesterol acyltransferase was added to mixtures at the completion of 24 h of incubation with CETP, the size of the HDL increased and the dissociated apoA-I returned to the fraction of d < 1.25 g/ml. analysis of the lipoprotein-deficient fraction of d > 1.25 g/ml isolated by ultracentrifugation and of the lower molecular weight fractions recovered after size-exclusion chromatography revealed that the dissociated apoA-I was not associated with significant quantities of either choleste
Int J Radiat Biol. 1993 Mar;63(3):279-88.
Ionizing radiation target groups of band 3 inserted into egg lecithin liposomes as determined by Raman spectroscopy.
Verma SP, Singhal A, Sonwalkar N.
Department of Community Health, Tufts University School of Medicine, Boston, MA 02111.
The purified integral membrane protein, band 3, from human erythrocytes was inserted into egg lecithin liposomes. The insertion of band 3 was determined from thermal transition data from the analysis of the C--H stretching region bands recorded at temperatures from 25 to -22 degrees C. Raman spectra show that band 3 considerably broadens and lowers the thermal transition of egg lecithin liposomes, suggesting the insertion of band 3. The band 3-inserted liposomes were irradiated with gamma-rays (40 Gy) and the radiation target groups were determined by the analysis of the structural sensitive Raman bands in the 1600-1700 cm-1 (amide I), 1200-1300 cm-1 (amide III) and 550-1030 cm-1 (side chain amino groups) regions. The radiation-sensitive groups as identified from Raman spectra in the region 550-1030 cm-1 are tyrosines and cysteines. The radiation-induced changes in the secondary structure were determined from amide I and III bands. Quantitative estimation using the curve fitting method shows that band 3 contains 44% total helix, 48% beta strand and 8% undefined plus turns (error +/- 4%). The secondary structure changes to 35% total helix, 42% total beta-strand and 23% turned and undefined upon irradiating band 3 containing liposomes. We suggest that ionizing radiation preferably damages tyrosine and cysteine side chain residues and reduces the amount of alpha-helical configuration of band 3.
Laxative online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8095277&dopt=Abstract lecithin
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