SELECTIVE INTERACTION OF VALINOMYCIN/K+ WITH THE CYTOCHROME BF COMPLEX OF CHLOROPLASTS - SYNERGISTIC EFFECT WITH MOA STILBENE ON EXTENT OF CYTOCHROME B(563) REDUCTION IN CONTINUOUS LIGHT

Valinomycin/K+ is shown to selectively interact at sub-micromolar concentrations with the cytochrome bf complex in thylakoid membranes, inducing a red shift of the ferrohaem b absorbance alpha-band, a slow down of post-illumination b-reoxidation and a corresponding increase of b-reduction level in continuous light. These effects of valinomycin/K+ are not related to its herd dissipating action, as they are not affected by nonactin. Presence of Kf is required. Phenomenologically the valinomycin/K+ effects are similar to those caused by 10 times higher MOA stilbene concentrations. However, synergism is observed between the two inhibitors, suggesting different modes of action. When both inhibitors are combined more than one haem b can be reduced by illumination.