Light-induced H+ Efflux from Intact Cells of Cyanidium caldarium |
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Authors: | Kura-Hotta Mariko; Enami Isao |
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Institution: | Department of Biology, Faculty of Science, Science University of Tokyo Kagurazaka, Shinjuku-ku, Tokyo 162, Japan |
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Abstract: | Light-induced pH changes in suspensions of an acidophilic unicellularalga, Cyanidium caldarium Geitler, were studied as a functionof the pH of the medium. In the neutral pH region, alkalizationof the medium due to photosynthetic CO2 uptake was observed.In the acidic pH region, illumination caused a significant decreasein the pH of the medium, indicating the efflux of H+ from thecells. Both the rate and extent of the pH decrease increasedas the pH of the medium was lowered to 3.0. The H+ efflux wasnot affected by 3-(3',4'-dichlorophenyl)-l,l-dimethylurea, butwas inhibited by phenylmercuric acetate. The fastest H+ effluxoccurred at 45°C, whereas its extent was almost constantfrom 25 to 50°C. The activity decreased at temperaturesabove 50°C and was inactivated completely at 60°C. Itsaction spectrum corresponded the spectrum for chlorophyll aabsorption. Results indicate that the light-induced H+ effluxis driven by photosystem I and is important in the maintenanceof the intracellular pH at the functional neutral region againsta steep pH gradient across the cell membrane. (Received May 6, 1981; Accepted August 8, 1981) |
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