Carlos Gitler

Microviscosity of the cell membrane.

Abstract The microvisocisty in the membrane interior of hemoglobin-free erythrocyte membranes, lymphocytes and submitochondrial particles was derived from an adequate comparison of the degree of fluorescence polarization of perylene when dissolved in the tested membranes and in a reference oil of known viscosity. The membranes tested showed a highly viscous liquid interior with microviscosities in the range of 100–200 cP. Trypsin digestion of hemoglobin-free erythrocyte membranes had almost no effect on the microviscosity while, on the other hand, phospholipase C digestion made the membranes much more fluid. The derived fusion activation energies for the different membranes are reported.

Photoactive covalent labeling of membrane components from within the lipid core.

Abstract Radioactive 1-Azidonaphthalene and 1-Azido-4-iodobenzene added to liposomes and sarcoplasmic reticulum membranes, are able to reach the liquid hydrocarbon like core, as demonstrated by encounter quenching of perylene fluorescence. Photoactivation converts the azides into the reactive nitrenes which label covalently the fatty acyl chains of the phospholipids. In addition, approximately half of the radioactivity is associated with membrane proteins. Only some 25% is released by exhaustive pronase treatment. Gel electrophoresis shows that the label is located in the Ca ++ -stimulated Adenosine triphosphatase and in a high molecular weight polypeptide. These results are discussed in terms of possible labeling of biological membranes from within the lipid core.

Thin-proteolipid films: a new approach to the reconstitution of biological membranes.

Abstract The extraction into n-decane of proteolipids composed of cytochrome c and a mixture of acidic and zwitter-ionic phospholipids, studied as a function of aqueous-phase pH, showed that optimal extraction occurred below pH 4.0 regardless of the anionic phospholipid used. The decane-soluble proteolipid readily allowed the formation of ultrathin black films whose electrical resistance was of the same magnitude as bilayers composed only of lipids. However significant differences in film capacitance were detected, being lower for the proteolipid than for equivalent lipid films. This model study establishes principles upon which the extraction of membrane proteins must be based and indicates the feasibility of reconstituting complex membrane functions in model thin-proteolipid films.

Catalysis of Ester Hydrolysis by Mixed Micelles containing

Model compounds are described for the study of the properties of amino acid side chains in the surface of micelles. Mixed micelles of N-α- mnyristoyl-L- histidine and cetyltrimethylammonium bromide catalyze the hydrolyses of p-nitrophenyl acetate and p-nitrophenyl caprylate at much higher rates than imidazole or histidinie do. The reaction shows a kinetic behavior similar to that of surface-catalyzed reactions.