Admon, A., Biochemistry Department, Weizmann Institute of Science, Rehovot, Israel
Shahak, Y., Biochemistry Department, Weizmann Institute of Science, Rehovot, Israel
Avron, M., Biochemistry Department, Weizmann Institute of Science, Rehovot, Israel

Utilizing oxonol VI as a transmembrane electric potential indicating dye, chloroplasts are shown to develop rapid transient light-induced and ATP-induced potentials. Following the large transient signal smaller steady-state potentials are maintained with either driving system. The ATP-induced potential in the dark depends upon preactivation of the light-triggered ATPase of the chloroplasts, and is inhibited by uncouplers, ionophores such as valinomycin, and energy-transfer inhibitors such as tentoxin, Dio-9 or DCCD. Nigericin increased the signal of both the light- and the ATP-induced reactions. The fact that relatively large transient membrane potentials are induced by either a dark-to-light transition or ATP in the dark provides an explanation for previously observed phenomena such as early kinetics of photophosphorylation and the ATP-induced luminescence. © 1982.