Electrophoretic mobility variations of Synechococcus PCC 7942 plasmalemma vesicles with nitrogen source

The electrophoretic mobility of cytoplasmic membrane vesicles from Synechococcus PCC 7942 cells adapted to low and high nitrate concentrations or to ammonium was measured by laser Doppler electrophoresis. The study of the mobility variations in the presence of different salts showed that specific interactions or binding of NO3− occurred on membranes from nitrate-adapted cells exclusively. The interactions between nitrate ions and the plasmalemma vesicle surface were related to the expression of the nitrate transport proteins. This was also illustrated by the mobility values observed in the absence of salt. Indeed, the mobilities were less negative as the amount of nitrate transport proteins was higher. In agreement with this observation, the plasmalemma vesicle mobility of the low nitrate medium-adapted cells was significantly lower than those of the high nitrate- and ammonium medium-adapted ones which were almost identical. The contribution of the positively charged segments of the nitrate binding protein to the surface charge variations was pointed out.