RESUMO
The interaction of L-Phe with the membrane components, i.e., lipids and proteins, has been discussed in the current literature due to the interest to understand the effect of single amino acids in relation to the formation of amyloid aggregates. In the present work, it is shown that L-Phe interacts with 9:1 DMPC (1,2-dimyristoyl-sn-glycero-3 phosphocholine)/DPPC (1,2-dipalmitoyl-sn-glycero-3 phosphocholine) mixtures but not in the 1:9 one. An important observation is that the interaction disappears when DPPC is replaced by diether PC (2-di-O-hexadecyl-sn-glycero-3-phosphocholine) a lipid lacking carbonyl groups (CO). This denotes that CO groups may interact specifically with L-Phe in accordance with the appearance of a new peak observed by Infrared spectroscopy (FTIR-ATR). The interaction of L-Phe affects the compressibility pattern of the 9:1 DMPC/DPPC mixture which is congruent with the changes observed by Raman spectra. The specific interaction of L-Phe with CO, propagates to phosphate and choline groups in this particular mixture as analyzed by FTIR-ATR spectroscopy and is absent when DMPC is dopped with diether PC.
Assuntos
Dimiristoilfosfatidilcolina , Fenilalanina , Fenilalanina/química , Fenilalanina/metabolismo , Dimiristoilfosfatidilcolina/química , Espectroscopia de Infravermelho com Transformada de Fourier , Bicamadas Lipídicas/química , Bicamadas Lipídicas/metabolismo , 1,2-Dipalmitoilfosfatidilcolina/química , 1,2-Dipalmitoilfosfatidilcolina/metabolismo , Lipídeos de Membrana/química , Lipídeos de Membrana/metabolismoRESUMO
Zeta potential and dipole potential measures are direct operational methodologies to determine the adsorption, insertion and penetration of ions, amphipathic and neutral compounds into the membranes of cells and model systems. From these results, the contribution of charged and dipole groups can be deduced. However, although each method may give apparent affinity or binding constants, care should be taken to interpret them in terms of physical meaning because they are not independent properties. On the base of a recent model in which the lipid bilayer is considered as composed by two interphase regions at each side of the hydrocarbon core, this review describes how dipole potential and zeta potential are correlated due to water reorganization. From this analysis, considering that in a cell the interphase region the membrane extends to the cell interior or overlaps with the interphase region of another supramolecular structure, the correlation of dipole and electrostatic forces can be taken as responsible of the propagation of perturbations between membrane and cytoplasm and vice versa. Thus, this picture gives the membrane a responsive character in addition to that of a selective permeability barrier when integrated to a complex system.
RESUMO
Comparison of the behavior of Laurdan in gel and in the liquid crystalline DPPC bilayers with that observed in chloroform and OctOH allow concluding that changes in the membrane lipid order cannot be ascribed to changes in viscosity of the local environment. Cholesterol acts as a spacer below the transition temperature of DPPC, promoting a disorder state in the acyl chain region. No evidence of water entrance has been detected with Laurdan up to 30% Cholesterol in DPPC in this condition. In contrast, Chol displaces to longer values the wavelength of Laurdan in membranes in the liquid crystalline state. This decrease in polarity occurs above 5% Chol and is directly related to the water extrusion produced by Chol. This effect is similar to that occurring in liquid crystalline membranes subjected to hypertonic stress. The behavior is comparable to that of Laurdan in OctOH at different water ratios below 5% Chol/DPPC. At higher ratios, other changes are evident.
Assuntos
2-Naftilamina/análogos & derivados , Colesterol/química , Lauratos/química , Bicamadas Lipídicas/química , 2-Naftilamina/química , Fluorescência , Lipídeos de Membrana/química , Solventes/químicaRESUMO
The values of capacitance of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE) monolayers on Hg, derived from cyclic voltammetry studies indicate that when the lipids are near the phase transition temperature fractures are formed at a critical area beyond that corresponding to the hydration shell of the lipids in the liquid expanded state. Similar fractures are inferred to be formed when an electric field is applied at constant area, at a breaking potential which is a function of the lipid species. These voltage values denote that energy involved in the transition induced by the electrical field is much higher for DMPE than for DMPC at low areas. This can be explained by the higher intermolecular lateral interactions by H-bonds between the ethanolamine and phosphate groups. However, at larger areas, the energy values for DMPC are as high as for DMPE which is understood to be due to the higher hydration of phosphocholine head groups. This finding gives a new insight in relation to the dynamics of the lipid head groups at the membrane interphase region in terms of the states of water between the lipids. This is congruent with previous results evaluated with the well known ΔΠ vs. surface pressure plots in monolayers of the same lipids at air-water interfaces.
Assuntos
Dimiristoilfosfatidilcolina/química , Fosfatidiletanolaminas/química , Água/química , Bicamadas Lipídicas/química , Lipídeos/química , TemperaturaRESUMO
The interaction of L-arginine with membranes composed by phospholipids with different degrees of methylation of the ethanolamine group was studied by means of surface and dipole potentials and surface pressure variations. The subsequent methylation of the amine head group appears to hinder the synergic response of the adsorption observed in phosphatidylethanolamine membranes. The kinetics of the binding process denotes that the methyl groups are relevant in regulating the specific interaction of the amino acid with the interface by hydrogen bonds. This response can be put in correlation with the function of signal transduction assigned previously to methyl lipids [F. Hirata and J. Axelrod, 1980] and appears to be relevant to understand the mechanism of insertion of arginine residues in peptides of biological interest.