1-palmitoyl-2-oleoylphosphatidylcholine and 1-anilino-8-naphthalenesulfonate

Green tea catechins consisting of catechin stereoisomers and their derivatives have been suggested to show biological activities through the interactions with cellular membranes. Their effects on membrane fluidity were comparatively studied by measuring fluorescence polarization of liposomal membranes prepared with phospholipids and cholesterol. All catechin stereoisomers reduced membrane fluidity by acting on the hydrophilic and hydrophobic regions of membrane bilayers at 20-500 microM. Both epicatechins in a cis form were more effective for reducing membrane fluidity than both catechins in a trans form. (-)-Epicatechin, (+)-epicatechin, (-)-catechin and (+)-catechin reduced membrane fluidity in increasing order of intensity. Such difference between optical isomers was increased by chiral cholesterol added to membrane lipids. In reversed-phase chromatographic evaluation, (-)-epicatechin and (+)-epicatechin were more hydrophobic than (-)-catechin and (+)-catechin, although hydrophobicity was not distinguishable between optical isomers. Stereospecificity in the membrane effects of catechin stereoisomers may be induced by the different hydrophobicity of geometrical isomers and the chirality of membrane lipid components. At lower concentrations (5-100 microM), (-)-epigallocatechin gallate and (-)-epicatechin gallate reduced membrane fluidity more significantly than (-)-epicatechin, suggesting that the intensive membrane effect contributes to the potent medicinal utility of (-)-epigallocatechin gallate.

Topics: 1-Naphthylamine; 1,2-Dipalmitoylphosphatidylcholine; Anilino Naphthalenesulfonates; Catechin; Chromatography, High Pressure Liquid; Diphenylhexatriene; Flavonoids; Fluorescence Polarization; Fluorescent Dyes; Liposomes; Membrane Fluidity; Membranes, Artificial; Phosphatidylcholines; Stereoisomerism; Structure-Activity Relationship

An amino-terminal deletion mutant (residues 1-43) of human apolipoprotein A-I (apo hA-I) has been produced from a bacterial expression system to explore the structural and functional role of these amino acids, encoded by exon 3, in apo hA-I. Lipid binding of apo delta (1-43)A-I and lipid binding of apo hA-I are very similar as assessed by surface activity, lipid association with palmitoyloleoylphosphatidylcholine (POPC) vesicles, and lipid association with plasma lipoproteins. Preliminary kinetic measurements appear to show that the reactivity of lecithin:cholesterol acyltransferase (LCAT) with the mutant is slightly decreased compared to wild-type apo hA-I. Collectively, these results indicate that the N-terminal region is not necessary for lipid binding or activation of LCAT. In contrast, there are significant structural differences between lipid-free apo delta (1-43)A-I and apo hA-I, as judged by denaturant-induced unfolding, binding of the fluorescent probe 1-anilinonaphthalene-8-sulfonate, surface balance measurements, and far- and near-ultraviolet circular dichroic spectroscopy. All spectral and physical measurements indicate apo delta (1-43)A-I has a folded, tertiary structure, although it is significantly less stable than that of apo hA-I. It is concluded that the N-terminal 43 residues are an important structural element of the lipid-free conformational state of apo hA-I, the absence of which induces a fundamentally different fold for the remaining carboxy-terminal residues, compared to those in native apo hA-I.

Topics: Anilino Naphthalenesulfonates; Apolipoprotein A-I; Binding Sites; Calorimetry; Circular Dichroism; Cloning, Molecular; DNA Primers; Escherichia coli; Fluorescent Dyes; Humans; Kinetics; Phosphatidylcholine-Sterol O-Acyltransferase; Phosphatidylcholines; Polymerase Chain Reaction; Protein Conformation; Protein Denaturation; Protein Folding; Recombinant Proteins; Sequence Deletion; Spectrometry, Fluorescence; Spectrophotometry, Ultraviolet; Substrate Specificity; Thermodynamics