Estimation of internal pH in cells of blue-green algae in the dark and under illumination

Carbonylcyanide m-chlorophenylhydrazone (CCCP) or nigericin induced translocation of H+ In the dark across the cell membrane of blue-green algae Plectonema boryanum and Anacystis nidulans. The direction of the H+ flux depended on the pH of the suspending medium. At acidic pH, an influx of H+ and at alkaline pH an efflux of H+ were observed. It is suggested that the influx takes place at pH'S higher than the "internal" pH and the efflux at pH's lower than that. The internal pH was estimated to be 7.4+/-0.2 for Plectonema boryanum and 7.5+/-0.1 for Anacystis nidulans. Similar H+ changes due to CCP were observed under illumination, where the light induced efflux of H+ was limited by the counter-flux of cations. The internal pH of cells in the light, estimated from the pH-dependent reversion in the rate of the H+ change, was about 8.5.