Effect of salts on the electrophoretic mobility of Synechococcus PCC 7942 plasmalemma vesicles from cells grown on different nitrogen sources

Abstract The modification of the membrane component composition in response to a change in the nitrogen source available to the cells exerts an influence on the number of electrostatic charges at the membrane surface, resulting in a variation in the surface and zeta potential determined from electrophoretic mobility measurements. The electrophoretic mobility of purified plasmalemma vesicles from Synechococcus Pasteur culture collection (PCC) 7942 cells, grown in the presence of nitrate or ammonium, was determined by laser Doppler electrophoresis in the absence or presence of different salts: NaCl, KCl, NaNO 3 and KNO 3 . By increasing the salt concentration, different variations in the mobility were observed on the two plasmalemma types. In the absence of added salts, the mobilities of the vesicles from ammonium-grown cells were always lower than those from nitrate-grown cells. In the presence of salts, the variations in the mobility were similar whatever anion was present with sodium, whereas the variations were completely different in the presence of different potassium salts. The most important effect was noted with KNO 3 on plasmalemma vesicles from nitrate-grown cells, i.e. a slow decrease in the mobility, indicating a higher negative charge density than that of the other salts. Both types of vesicle discriminated between the anions in the presence of potassium, but were practically insensitive to the anions in the presence of sodium. The presence of potassium cations induced a specific interaction between the Synechococcus membrane and nitrate.