Study of the interaction of GB virus C/Hepatitis G virus fusion peptides belonging to the E2 protein with phospholipid Langmuir monolayers.

In order to determine the ability of 1,2-dipalmitoyl phosphatidylcholine (DPPC) and 1,2-dioleoyl phosphatidylglycerol (DOPG) to host peptide sequences belonging to the E2 protein of GBV virus C/Hepatitis G virus, the behaviour of Langmuir monolayers formed by these phospholipids and E2 (12-26), E2 (354-363) and E2 (chimeric) peptide sequences was analysed from data of surface pressure (π) versus area per molecule (A) isotherms, compression modulus (Cs-1), excess Gibbs energy of mixing (ΔGexc) and total Gibbs energy of mixing (ΔGmix). Three different behaviours were observed. Mixed films of E2 (12-26) with DPPC or DOPC showed negative values for the excess thermodynamic functions, and thus attractive interactions between mixed films components are greater than in ideal films. Mixtures of E2 (354-363) with DPPC or DOPG, exhibited positive values of excess functions, evidencing weaker interactions in the mixed films in relation to those of pure components. Finally, positive and negative excess functions were observed in E2 (chimeric)/DPPC or DOPG mixed films, depending on their composition. In short, the interaction between the phospholipids used in this work as models of cell membranes and E2 peptides varies with the type of phospholipid and the nature of the peptide (size, bulky, hydrophobicity and electric charge).

Characterization of the binary mixed monolayers of α-tocopherol with phospholipids at the air-water interface.

The mixed Langmuir monolayers composed of model constituents of biological membranes, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 2-oleoyl-1-palmitoyl-sn-glycero-3-phosphocholine (POPC), and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), were investigated to provide information on the intermolecular interactions between these membrane components and the physiologically active vitamin E-α-tocopherol (TF), as well as on the phase behavior of these mixed systems. Additionally, topography of these monolayers transferred onto the mica support was investigated by the inverted metallurgical microscope. Morphological characteristics were directly observed by Brewster angle microscopy (BAM). From the surface pressure-area isotherms and the analysis of physicochemical parameters (compressibility and mean molecular area at the maximum compressibility) it was found that depending on the acyl chains saturation degree, TF has different effect on the phospholipids. In the case of DPPC, the addition of TF to the phospholipid film causes destabilization of the ordered hydrocarbon chains, while in the POPC/DOPC-TF systems, the attractive interactions are responsible for the monolayer increased stability. Thus, the results of these studies confirm the hypothesis that α-tocopherol may play a role in the stabilization of biological membranes.

Anfotericina Liposomal: Una aproximación fisicoquímica al conocimiento de su mecanismo de acción / Liposomal Amphotericin: A physical-chemistry approach to the knowledge of its mechanism of action

El análisis de las isotermas presión superficial (pi) - área molecular (A), así como el de las curvas del módulo de compresibilidad (Cs-1) en función de la presión superficial correspondientes a monocapas mixtas de anfotericina B (AmB) y dipalmitoil fosfatidil serina (DPPS) extendidas sobre subfases de diferentes pH, muestra la existencia de importantes interacciones entre ambos componentes, sugiriendo la formación de complejos estables en la interfase aire/agua constituidos por dos moléculas de AmB orientadas horizontalmente y una de DPPS en posición vertical. Las atracciones de tipo iónico y el establecimiento de enlaces de hidrógeno entre los grupos polares de los componentes son los responsables de las interacciones mutuas, las cuales dependen del pH de la subfase como consecuencia del diferente estado de ionización de los grupos implicados en la interacción (grupos carboxílico y amino de la AmB y fosfato, carboxílico y amino del DPPS). La aplicación de la regla de las fases a las transiciones de fase de las monocapas mixtas permite conocer la miscibilidad del complejo con el componente en exceso (AmB o DPPS) cuando la proporción de éste en la mezcla excede a la requerida para la formación del complejo de estequiometria 2:1. La existencia de interacciones AmB/fosfolípido permite formular una interpretación acerca del mecanismo de acción de la AmB sobre la membrana celular de los hongos, así como de su menor toxicidad sobre el huésped cuando se administra en forma de liposomas (AU)