LIGHT-INDUCED OXIDATION OF A CHLOROPLAST B-TYPE CYTOCHROME AT -189 degrees C.
The b-type cytochromes of chloroplasts have heretofore been viewed as photosynthetic electron carriers that probably occupy an intermediate position in a light-induced electron flow. The oxidation-reduction of such intermediate electron carriers, being removed from the primary photochemical reaction linked to photon capture by chlorophyll, would be expected to show a temperature dependence. Evidence has now been obtained that cytochrome b(559) is photooxidized at -189 degrees C and that this photooxidation can be induced only by "short-wavelength" monochromatic light which activates the oxygen-evolving system in chloroplasts (photosystem II). In appears, therefore, that photooxidation of cytochrome b(559) is closely linked with photon capture by the chlorophyll pigments characteristic of photosystem II.
DEPARTMENT OF CELL PHYSIOLOGY, UNIVERSITY OF CALIFORNIA, BERKELEY.
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Knaff
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Arnon