EFFECT OF OSMOTIC STRESS ON THE INTERFACIAL PROPERTIES OF LIPID MEMBRANES.

ARROYO, J.; DISALVO, E ANIBAL; GRAMAJO, M; FRIAS, M DE LOS ANGELES

San Javier

Congreso; REunion de la Sociedad Argentina de Biofisica; 2012

SAB

Osmotic stress has been used to induce water permeation across lipid and cell membranes (1) and to study the interbilayer forces due to hydration (2). However, little is known about the effect caused by dehydration on the membrane structure and specifically on the reorientation of polar head groups and its associated water molecules (3, 4). These modifications may possibly affect the electrostatic and non electrostatic forces driving peptide and aminoacid insertion into lipid bilayers. In this regard, recent results have shown that water pockets due to kinks in saturated lipids or water clusters in unsaturated ones may explain the insertion of polar or positively charged aminoacids into the hydrophobic membrane core (5). In this work we present an analysis of the water state near the membrane surface when an osmotic stress is imposed by the external addition of polyethylenglycol or other water sequestering osmolyte. The effect is followed by measuring the bands of water bound to lipids and the bands corresponding to the hydration sites of the lipids (CO and PO). In addition, fluorescent measures allow determining the conditions at which defects with water can be formed. The structural picture derived from this analysis fits satisfactorily with the thermodynamic description of interfacial properties derived from surface tension measurements at different surface pressures (6).