Studies on Ion Transport in Cells of Photosynthetic Bacteria

II. Analysis of Reversed Hydrogen Ion Change

Abstract

The direction of light-induced H⁺ transport in cells of Rhodospirillum rubrum was outward in NaCl solution. The direction of the light-induced H⁺ change was reversed by the addition of NH₄⁺ and amine, and the reversal of H⁺ change was influenced by the pH of the medium. In NH₄Cl solution, light-induced H⁺ transport was outwardly directed at acid pH (<pH 5.9), and inwardly directed at alkaline pH (>pH 5.9). At near pH 5.9 the light-induced H⁺ change showed a biphasic time-course. The two-directional H⁺ changes were inhibited by the addition of carbonyl cyanide m-chlorophenylhydrazone (CCCP) and antimycin A.
The pH value at which the direction of H⁺ change was reversed was dependent on the Cl^-/NH₄⁺ ratio in the medium. The reversal pH was 5.9 at Cl^-/NH₄⁺=1; it moved to the alkaline side on increasing the Cl^-/NH₄⁺ ratio.
Reversal of the H⁺ change was also observed in the presence of acetate or phosphate.
A possible mechanism of H⁺ transport in cells of Rhodospirillum rubrum was discussed in relation to anion and NH₄⁺ transport.