The role of plastoquinone and β-carotene in the primary reaction of plant Photosystem II |
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Authors: | David B Knaff Richard Malkin J Clark Myron Marshall Stoller |
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Institution: | Department of Cell Physiology, University of California, Berkeley, Calif. 94720 U.S.A. |
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Abstract: | Extraction of Triton Photosystem II chloroplast fragments with 0.2% methanol in hexane for 3 h results in the removal of 90 to 95% of the plastoquinone in the original preparation. The extracted fragments (chlorophyll : plastoquinone ratio, 900 : 1) showed no P-680 photooxidation at 15 K after a single laser flash. The extracted fragments also showed no light-induced C-550 absorbance change at 77 K. Reconstitution of the primary reaction of Photosystem II, as evidenced by restoration of low-temperature photooxidation of P-680, could be obtained by the addition of plastoquinone A but not by the addition of β-carotene. The addition of β-carotene plus plastoquinone A restored the C-550 absorbance change. These results indicate that plastoquinone functions as the primary electron acceptor of Photosystem II and that β-carotene does not play a direct role in the primary photochemistry but is required for the C-550 absorbance change. |
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Keywords: | Address reprint requests to Dr Malkin at the University of California |
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