Abstract
Abstraet-Ultrasonication of isolated Pisum sativum chloroplasts removed ferredoxin, ferredoxin-NADP+ reductase and plastocyanin. Photoreduction of NADP+, with the ascorbateDCIP couple as electron donor, was restored on the addition of these three proteins. When oxygen replaced NADP+ as the ultimate electron acceptor in this reaction, plastocyanin alone was required. The requirement for plastocyanin in ultrasonically treated chloroplasts appeared to be inversely related to the requirement for DCIP in mediating ascorbate oxidation. Heating fresh chloroplasts to 55” made the addition of DCIP and plastocyanin unnecessary in this reaction. This need for plastocyanin was induced by ultrasonic treatment of these heated chloroplasts. The results are interpreted as further evidence for the role of plastocyanin in photochemical electron transport.
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