Nature of light-induced absorbance changes at 682 m{micro} and 702 m{micro} in photosynthesis of Anacystis nidulans |
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Authors: | MURATA, NORIO TAKAMIYA, ATUSI |
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Affiliation: | Department of Biophysics and Biochemistry, Faculty of Science, University of Tokyo Hongo, Tokyo, Japan |
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Abstract: | Light-induced absorbance changes in the region around the redabsorption band of chlorophyll a were measured in cells andlamella fragments of Anacystis nidulans. In both materials,absorbance decreases were observed at 702 mµ and 682 mµ.(The pigments are designated as P700 and P680.) The nature ofP680 was investigated with special reference to its relationshipto P700. In the cells, light absorbed by chlorophyll a causedan absorbance decrease at 682 mµ; Simultaneous illuminationwith light absorbed by phycocyanin caused a partial recoveryof the absorbance decrease. Similar results were observed withthe light-induced absorbance change at 702 mµ. This indicatesthat P680 is also an electron carrier in the electron transportchain and occupies a place between the two photoreactions. Inlamella fragments, both the light-induced reversible absorbancechanges of P680 and P700 appeared in the presence of an electrondonor system; i.e., ascorbate and 2,6-dichlorophenolindophenolor N,N,N',N'-tetramethyl-l,4-phenylenediamine. The experimentsin which the oxidation-reduction potential of the reaction mediumwas changed showed that both P680 and P700 are one-electroncarriers, having a normal oxidation-reduction potential of 0.44v (assuming that the normal oxidation-reduction potential ofthe ferricyanide-ferrocyanide system is 0.409 v). A possibilitywas suggested that the absorbance change observed at 682 mµis another expression of the oxidation-reduction reaction ofP700). (Received October 30, 1968; ) |
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