title: The role of plastoquinone and beta-carotene in the primary reaction of plant photosystem II.
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 beta-carotene. The addition of beta-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 beta-carotene does not play a direct role in the primary photochemistry but is required for the C-550 absorbance change.
mesh_terms: D002338:Carotenoids / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism*; D003580:Cytochromes / Q000378:metabolism; D007834:Lasers; D008027:Light; D010084:Oxidation-Reduction; D010777:Photochemistry; D010785:Photophosphorylation; D010944:Plants; D010971:Plastoquinone / Q000378:metabolism*; D011092:Polyethylene Glycols; D011809:Quinones / Q000378:metabolism*
chemical_list: D003580:Cytochromes; D011809:Quinones; D002338:Carotenoids; D011092:Polyethylene Glycols; D010971:Plastoquinone