Rate Of Photoreaction Research Articles

Exogenous Manganese as an Electron Source for Both Photosystem II and Radical Superoxides

Exogenous manganese acts as an electron source for both photosystem I1 (PS 11) and radical superoxides formed after PS I. This conclusion is supported by measurements of external acidification when chloroplasts containing exogenous manganese and methyl viologen are illuminated. The acidification and increased oxygen consumption when manganese was added shows two moles of protons to be produced per mole of oxygen consumed. Reactions for manganese oxidation preceding PS I1 and following PS I are given with the net result: 2H2O + Mn2+ + O2 ͛4 MnO2 + H2O2 + 2H+ This reaction was shown to reverse in the dark and to have a chlorophyll dependency for both the rate of the forward photoreaction and reverse dark reaction. The pH-dependency shows manganese can compete with water as an electron source for PS II only under alkaline conditions and the electrochemical potentials for the competition are discussed in terms of the half reactions involved.

Functionality and structure of polymers. I. Photoreaction and fluorescence of polyesters having pendant anthryl groups

AbstractVarious polyesters having pendant (9‐anthryl)methyl groups were prepared from 2‐(9‐anthryl)methylpropane‐1,3‐diol and the esters or chlorides of dicarboxylic acids. These polyesters are poly[2‐(9‐anthryl)‐methylpropane‐1,3‐diyl‐oxy‐(9‐anthryl)methylmalonyl‐oxy](PA‐1A), poly‐[2‐9‐anthrylmethylpropane‐1,3‐diyl‐oxysuccinyloxy](PA‐2), poly‐[2‐9‐anthrylmethylpropane‐1,3‐diyl‐oxyadipyloxy](PA‐4), poly[2‐(9‐anthryl)methylpropane‐1,3‐diyl‐oxysebacyloxy] (PA‐8), poly[2‐(9‐anthryl)methylpropane‐1,3‐diyl‐oxy‐(1‐naphthyl)methylmalonyloxy](PA‐1N), and poly[2‐(9‐anthryl)methylpropane‐1,3‐diyl‐oxyterephthaloyloxy](PA‐Ph). Although the absorption spectrum of the anthryl group is not influenced by the change in the environment in which the anthryl group is located, the fluorescence spectra show characteristic change reflecting the environment around the chromophore. Dimer, aggregates, or excimer fluorescence of anthryl groups and energy transfer from naphthyl to anthryl groups for PA‐1N were discussed. The rates of photodimerization of anthryl groups determined spectroscopically in dilute solutions for these polyesters and their monomer model compound(1,3‐diacetoxy‐2(9‐anthryl)methylpropane) (MA), were in the following order; PA‐8 > PA‐4 > PA‐1A > PA‐2 > PA‐Ph > MA. The effects of polymer structure on the photoreaction were discussed on the basis of information on molecular interactions obtained by fluorescence spectroscopy. The fraction of intramolecular cyclization was estimated from dependence of the rate of photoreaction on the concentration of the polyesters. When anthryl groups are linked by a long, flexible polymethylene chain (PA‐8), intramolecular process predominates whereas intermolecular dimerization proceeds almost exclusively for a rodlike molecule(PA‐Ph). These results are discussed from the viewpoint of the structure–functionality relationship in polymeric systems.

Control of excitation transfer in photosynthesis. IV. Kinetics of chlorophyll a fluorescence in Porphyra yezoensis

The kinetics of chlorophyll a fluorescence were measured at 685 nm in intact cells of Porphyra yezoensis during alternate illumination of the organism with two colors of light, one absorbed by phycoerythrin and the other by chlorophyll a. Two components of fluorescence change overlapping each other in time were separated; the fast component may be controlled by the rate of Photoreaction II which competes with the fluorescence emission process, and the slow component by the light-induced change in excitation transfer between two pigment systems as suggested in our previous study 6. The kinetics of the slow change in fluorescence yield were extensively investigated. Terms, “State I” and “State II” are used to describe the state of excitation transfer. In the State I a lesser amount of excitation energy is delivered in Pigment System I and greater to Pigment System II than in the State II. The conversion of the states is achieved by the selective illumination of pigment systems. The conversion from the State I toward the State II occurred under Light II (light absorbed by Pigment System II) with a half time of about 10 sec, and it saturated at a light intensity of less than 1000 ergs×cm −2×sec −1. The reverse conversion occurred under Light I (light absorbed by Pigment System I) with a half time of about 5 sec, and it saturated at about 10 000 ergs×cm −2×sec −1. Light I and Light II competed with each other in the interconversion of the states.

Control of excitation transfer in photosynthesis. II. Magnesium ion-dependent distribution of excitation energy between two pigment systems in spinach chloroplasts

1. 1. Effects of metal ions on the yields of chlorophyll a fluorescence were investigated in spinach chloroplasts. At room and liquid-nitrogen temperatures, addition of Mg 2+ increased the yields of two emissions of chlorophyll a, having peaks at 684 and 695 nm which were emitted from pigment system II and decreased the yield of another emission of chlorophyll a at about 735 nm which was emitted from pigment system I. Mg 2+ also changed the pattern of the fluorescence induction at room temperature to increase the variable component of fluorescence. 2. 2. Effects of Mg 2+ on the quantum yields of the two photoreactions were investigated in a region of weak light intensities. Mg 2+ accelerated the rate of photoreaction II measured by the Hill reaction with 2,6-dichlorophenolindophenol and depressed the rate of photoreaction I measured by the NADP + reduction in the presence of reduced 2,6-dichlorophenolindophenol and 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea. 3. 3. These facts indicate that Mg 2+ controls the distribution of excitation energy between the two pigment systems and that the control consists mainly in change in rate of excitation transfer from the bulk chlorophyll a molecules in pigment system II to those in pigment system I; namely, Mg 2+ suppresses the spillover of excitation energy from pigment system II to pigment system I.