Analysis of photosystem II using particle II preparation III. Roles of cytochrome b559with different redox potentials and plastocyanin in the photosynthetic electron transport system1

摘要

1. Using the P-II preparation (photosystem II preparation), the functional sites for Cyt-b559with different redox potentials and for plastocyanin in the non-cyclic electron transport chain of chloroplasts were investigated.2. In the absence of plastocyanin, the P-II preparation showed no light-induced absorption changes in Cyt-b559. However, upon the addition of a sufficient amount of plastocyanin, remarkable photooxidation of this cytochrome was observed at room temperature.3. Parallel measurements of the light-induced absorption changes in both Cyt-b559and plastocyanin revealed a close relationship between them, and indicated that Cyt-b559and plastocyanin are located in series on the main path of the electron transport chain involving two photoreactions in PS-II.4. Difference spectra and action spectra for the light-induced absorption changes in Cyt-b559and plastocyanin offered additional evidence in support of the above conclusion.5. Analysis of the relationship between the activity of ferricyanide Hill reaction and the contents of Cyt-b559of different redox potentials showed that both forms of Cyt-b559(i.e. high- and low-potential forms) play important roles under physiological conditions, being on the main pathway of the electron transport chain connecting PS-II and PS-I.6. To these findings it is possible to give reasonable explanations based on our scheme presented previously, which suggested that PS-II contains not one but two different photoreactions. This scheme is much more elaborately supported by this study which shows the functional sites for Cyt-b559with two different potentials.