Mechanism of activation and spectral shift of the F-695 emission band in chloroplasts as induced by 1,10-phenanthroline

1. Changes in the fluorescence emission spectrum of chloroplast, at 77 °K, induced by chaotropic reagents and 1,10-phenanthroline, were analyzed.2. Fourth-derivative analysis of the emission spectra identified the exact location of a new band (referred to as “F-700”) at 700 nm and showed that the conversion of F-695 into F-700 does not occur by a gradual red-shift of the F-695 band, but by the appearance of a new band at 700 nm at the expense of an intensity decrease in the F-695 emission.3. F-700 shows two distinct fluorescence characteristics, namely the wavelength of its emission maximum and its intensity, but still retains the principal properties of F-695 such as steep temperature dependence at low temperatures, transient phenomena at 77 °K, and an excitation spectrum of the Photosystem II type. Thus F-700 is concluded to be a modified state of F-695.4. In addition to the compounds of the urea-guanidine class, inorganic anions such as SCN^?, I^? and ClO₄^? were active in the transformation. The specificity and theorder of effectiveness of these reagents indicated that their action is that of chaotropic reagents. Transformation was inhibited by the presence of compounds such as sugars, salts, alcohols and dimethylsulfoxide which seem to affect the activity of water.5. 5-Methyl-1,10-phenanthroline partly substituted for the action of 1,10-phenanthroline, while the other six different derivatives of 1,10-phenanthroline and a few other bifunctional ligands were inactive. The structure-activity relations and the effective concentrations in the transformation differed greatly from those of the inhibition of the electron transport chain, suggesting that the action of 1,10-phenanthroline in the transformation is a yet unrecognized action of this reagent on Photosystem II.6. Transformation was generally observed in chloroplast preparations from 11 different higher plants and two species of algae tested. In Lolium sp. the transformation was partly attained by 1,10-phenanthroline alone.7. From these results, the state of F-695 in chloroplast membranes and the mechanism of transformation into F-700 are discussed.