EFFECTS OF IONOPHOROUS ANTIBIOTICS ON LIGHT-INDUCED INTERNAL AND EXTERNAL HYDROGEN ION CHANGES AND PHOSPHORYLATION IN BACTERIAL CHROMATOPHORES

The effects of ionophorous or transportmediating antibiotics, valinomycin, nigericin, monensin, X-206, X-537A, and dianemycin on the lightinduced external and internal H+ changes of Rhodospirillum rubrum and Chromatium chromatophores were studied under phosphorylating and nonphosphorylating conditions. Valinomycin increased the rate and magnitude of the light-induced external pH rise in the presence of K+, but inhibited the apparent lightinduced internal acidification, as measured by bromothymol blue-spectrophotometric method. Nigericin, X-206, X-537A, and monensin decreased the lightinduced external pH rise, but increased the light-induced bromothymol blue change. Dianemycin either increased or inhibited both the bromothymol blue and external H+ changes, depending upon its concentration. Under phosphorylating conditions, these antibiotics had little effect on the phosphorylation-dependent external pH rise due chiefly to adenosine triphosphate synthesis in either the presence or absence of K+ or Na+. Combinations of valinomycin and nigericin, or valinomycin and uncouplers did not produce synergistic effects. Possible mechanisms for the observed effects of ionophorous antibiotics on the internal and external H+ changes and the processes of energy transduction are presented. Differences between the actions of ionophorous antibiotics on bacterial chromatophores and chloroplasts are discussed. © 1969, American Chemical Society. All rights reserved.