Effect of DMBQ, PNDA, DCMU, and DBMIB on net proton movements in WT Synechocystis cells. The light was switched on (arrow down) and off (arrow up) as indicated. The cells were suspended in 0.2 mM TES-KOH buffer (pH 8.0) containing 15 mM NaCl. DMBQ (final concentration, 1 mM) (D to E), PNDA (3 mM) (G to I), DCMU (20 μM) (B, E, and H), and DBMIB (10 μM) (C, F, and I) were added as indicated. All additions were done prior to illumination.