Acta Physiologica 71. (1988)
1. szám - Abstracts of the lectures and posters delivered and demonstrated at the XVI. MEMBRANE TRANSPORT SYMPOSIUM, Sümeg, May 12-16, 1986, Hungary - I. LECTURES - A. Bérczi: Surface charge density of biomembranes
Abstracts Surface charge density of biomembranes A. BÉRCZI INSTITUTE OF BIOPHYSICS, BIOLOGICAL RESEARCH CENTER, HUNGARIAN ACADEMY OF SCIENCES, SZEGED, HUNGARY Biomembranes, as structural and functional units consisting of different lipids and proteins, play an important role in the biochemical and biophysical properties of living cells. Characteristically for all kinds of biomembranes, certain parts of molecules with amphiphilic character can be ionized at the membrane/water interface, i.e. membranes carry electrica lsurface charges. As far as we know, the average surface charge density of biomembranes has always proved to be negative and has never exceeded the value of —40 mC.m-2. We have determined the average surface charge density of different membrane fractions from wheat roots using (1) the titration by monovalent and divalent cations of 9-aminoacridine fluorescence and (2) the Gouy— Chapman theory for the electric double layer. The method is valuable for comparative studies but results in absolute values for surface charge density which differ from that which can be obtained by measuring the electrokinetic mobility of membrane vesicles. In recent theoretical work, however, it has been assumed that (1) “surface” charges are located in the hydrophilic region about 1 nm from the hydrophobe/hydrophile interface and (2) there is an additional solvent drag caused by parts of molecules sticking out from the hydrophobic part of the membranes into the electric double layer. When these are taken into consideration in interpretating experimental results obtained in the electrokinetic studies, the absolute values obtained by the two methods mentioned above prove to be in good agreement. The knowledge of surface charge density is important where ions interact somehow' with membranes. It takes place in all ion transport processes through membranes and in all enzyme reactions where membrane-bound enzyme interacts with charged substrates and/or products. In such cases the real kinetic parameters can be calculated only if the surface charge density of the membrane is known. Acta Physiologica Hungarica 71, 1988