The reversible photoconversion of Chenopodium chlorophyll protein and its control by the apoprotein structure

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The reversible photoconversion of Chenopodium chlorophyll protein, CP668〓CP743, is strongly dependent on the pH of the solution. The photoconversion of CP668 was inhibited by a high pH, whereas a low pH inhibited the photoconversion of CP743. Transfer of CP668 to an alkaline pH caused a red shift of the 277-nm band in the UV absorption spectrum, whereas transfer of CP743 to an acidic pH caused a blue shift of the 280-nm band. The UV absorption difference spectrum between the acidic and alkaline solutions of CP668 showed a positive peak at 293 nm and a negative peak at 272 nm. From the pH titration curve of CP668, the pK values of 9.4 and 11.1 were determined. The alkaline titration curve of the 293-nm band gave an inflection point at pH 11.2. S-S reagents, β-mercaptoethanol and dithiothreitol, and KI were inhibitory to CP-668 photoconversion, but SH reagents, N-ethylmaleimide and p-chloromercuribenzoic acid, were not. The chemical modification of tyrosine residues, and the destruction of S-S bridges in the apoprotein inhibited CP668 photoconversion. From these results we concluded that the reversible. photoconversion is controlled by the conformation of the apoprotein in CP668.
日本植物生理学会の論文