References: Lecithin
Biophys J. 1992 Jul;63(1):78-88.
Transport methods for probing the barrier domain of lipid bilayer membranes.
Xiang TX, Chen X, Anderson BD.
Department of Pharmaceutics, University of Utah, Salt Lake City 84112.
Two experimental techniques have been utilized to explore the barrier properties of lecithin/decane bilayer membranes with the aim of determining the contributions of various domains within the bilayer to the overall barrier. The thickness of lecithin/decane bilayers was systematically varied by modulating the chemical potential of decane in the annulus surrounding the bilayer using different mole fractions of squalene in decane. The dependence of permeability of a model permeant (acetamide) on the thickness of the solvent-filled region of the bilayer was assessed in these bilayers to determine the contribution of this region to the overall barrier. The flux of acetamide was found to vary linearly with bilayer area with Pm = (2.9 +/- 0.3) x 10(-4) cm s-1, after correcting for diffusion through unstirred water layers. The ratio between the overall membrane permeability coefficient and that calculated for diffusion through the hydrocarbon core in membranes having maximum thickness was 0.24, suggesting that the solvent domain contributes only slightly to the overall barrier properties. Consistent with these results, the permeability of acetamide was found to be independent of bilayer thickness. The relative contributions of the bilayer interface and ordered hydrocarbon regions to the transport barrier may be evaluated qualitatively by exploring the effective chemical nature of the barrier microenvironment. This may be probed by comparing functional group contributions to transport with those obtained for partitioning between water and various model bulk solvents ranging in polarity or hydrogen-bonding potential. A novel approach is described for obtaining group contributions to transport using ionizable permeants and pH adjustment. Using this approach, bilayer permeability coeff
Anesth Analg. 1993 Jul;77(1):7-11.
Anesthesia by n-alkanes not consistent with the Meyer-Overton hypothesis: determinations of the solubilities of alkanes in saline and various lipids.
Taheri S, Laster MJ, Liu J, Eger EI 2nd, Halsey MJ, Koblin DD.
Department of Anesthesia, University of California, San Francisco 94143-0464.
Because deviations from the Meyer-Overton rule may provide insights into the attributes of the anesthetic site of action, we characterized the solubility of the n-alkanes in various hydrophobic solvents (n-tetradecane, olive oil, n-octanol, and lecithin) as well as saline using variations on standard techniques. Increasing alkane chain length correlated with a decrease in solubility in saline and an increase in solubility in the hydrophobic solvents. The product of solubility in the hydrophobic solvents x the partial pressure (in atmospheres) required to produce anesthesia (i.e., the Meyer-Overton rule) did not produce a constant for any one of these solvents. The means and standard deviations for the products were: tetradecane, 65 +/- 103; olive oil, 33 +/- 63; n-octanol, 64 +/- 129; and lecithin, 16 +/- 26. Thus, our data suggest that the n-alkanes (especially those longer than n-heptane) do not follow the Meyer-Overton rule.
Laxative online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8317750&dopt=Abstract lecithin
Biol Neonate. 1995;67(1):34-8.
The presence of prolidase activity in amniotic fluid and its evaluation as a maturity test.
Gurdol F, Genc S, Yalcin O, Gultepe M.
Department of Chemical Pathology and Human Metabolism, Royal Free Hospital, London, UK.
Prolidase (EC: 3.4.13.9) catalyses the hydrolysis of the peptide bond involving the imino nitrogen of proline or hydroxyproline. Because of the high proportion of imino acids in collagen, this enzyme plays an important role in its degradation. Since collagen turnover rate is expected to be high during fetal growth, the level of prolidase activity may reflect the degree of fetal maturation. In this study, amniotic fluid prolidase I activity was measured in term and preterm pregnancies. Lecithin concentration, which has been widely used for predicting fetal lung maturity, was also measured. Prolidase I activity was positively correlated with lecithin levels (n = 30; r = 0.42; p < 0.02), and also with birth weight of the babies (n = 30; r = 0.52; p < 0.01) in the term-mature group. Dysmature babies had significantly lower prolidase I activity in the amniotic fluid which was thought to be indicative of growth retardation.
Laxative online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7748973&dopt=Abstract lecithin
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