Co-Authors:
BEN Hayyim, G., Biochemistry Department, Weizmann Institute of Science, P. O. Box 26, Rehovot, Israel
Avron, M., Biochemistry Department, Weizmann Institute of Science, P. O. Box 26, Rehovot, Israel
Abstract:
Cytochrome composition and light‐induced absorbance changes of cytochromes b and f in isolated chloroplasts have been measured in the α‐band region utilizing dual‐wavelength spectrophotometry. Three cytochromes appeared in reduced minus oxidized spectra, whereas only two of them, namely, cytochrome f and a cytochrome b appeared in light‐induced difference spectra. Light‐induced changes of cytochrome b and cytochrome f, indicated that both are located in the part of the electron transport chain joining the two photosystems. The following sequence is supported by the evidence presented: Photosystem 2 → cytochrome b→ cytochrome f→ photosystem 1. 3‐(3,4‐Dichlorophenyl)‐1,1‐dimethyl urea was found to act in the region between photosystem 2 and cytochrome b since the photoinduced oxidation of both cytochromes but not of their reduction were observed in its presence. A site for ATP formation is suggested to be localized in the same region, since in the light the presence of uncouplers or photophosphorylating reagents induced a more reduced steady‐state of both cytochromes. Copyright © 1970, Wiley Blackwell. All rights reserved