AFFINITY FOR OXYGEN IN PHOTOREDUCTION OF MOLECULAR OXYGEN AND SCAVENGING OF HYDROGEN PEROXIDE IN SPINACH CHLOROPLASTS |
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Authors: | Kozi Asada Yoshiyuki Nakano |
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Institution: | The Research Institute for Food Science, Kyoto University, Uji, Kyoto 611, Japan |
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Abstract: | Abstract— The apparent K m for O2 in the photoreduction of molecular oxygen by spinach class II chloroplasts and photosystem I subchloroplast fragments was determined. In both cases, a value of 2 ∼ 3 μ M O2 was obtained. The reaction rate constant between O2 and P-430, the primary electron acceptor of PS I, is estimated to be ∼ 1.5 × 107 M -1 s-1 and the factors affecting the production of superoxide by the photoreduction of O2 in chloroplasts are discussed. Preliminary evidence is presented indicating the occurrence of an azide-insensitive scavenging system for H2O2 in chloroplast stroma. |
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