Action of some derivatives of 1,10-phenanthroline on electron transport in chloroplasts.

The effectiveness and the mode of inhibitory action of some derivatives of 1,10-phenanthroline and a few other substances on 2,6-dichlorophenolindophenol (DCIP) photoreduction and fluorescence induction at room temperature in spinach chloroplasts were compared in this paper. 4,7-Dimethyl-1,10-phenanthroline was the most potent inhibitor [pI50 (-log10 of molar concentration of inhibitor giving 50% inhibition), 5.9] examined, and 5-methyl-1,10-phenanthroline (pI50, 4.2) was as potent as 1,10-phenanthroline (pI50, 4.4), in the case of DCIP photoreduction. The order of inhibition by 4,7-dimethyl-1,10-phenanthroline (n=2) was different from that of 1,10-phenanthroline and 5-methyl-1,10-phenanthroline (n=1), under the experimental conditions used. Fluorescence induction was diminished by 4,7-dimethyl-1,10-phenanthroline or 5-methyl-1,10-phenanthroline with the same pattern as 1,10-phenanthroline, but the effective concentrations varied corresponding to the pI50 values for the inhibition of DCIP photoreduction. Metal ions which form a chelate complex with phenanthroline of high stability constant prevented the inhibition of both DCIP photoreduction and fluorescence induction. From these results, the structure-activity relations and the mode of inhibition of the photosynthetic electron transport chain by these reagents are discussed.