PHOTOCHEMICAL GENERATION OF REDUCED QUINONE CATALYSTS OF PHOTOSYSTEM I CYCLIC PHOTOPHOSPHORYLATION ACTIVITY

When reaction mixtures containing 9,10-anthraquinone-2-sulfonate and chloroplasts poisoned with 3–(3,4-dichlorophenyl)-l, l′-dimethylurea were illuminated with white light, photosystem I-catalyzed cyclic photophosphorylation was observed. Illumination of identical reaction mixtures with red light produced no ATP synthesis. This phenomenon is due to photoreduction of the anthraquinone which is supported by the electron donor activity of Tricine buffer. The photoreduction reaction was used to generate reduced catalysts (anthraquinone sulfonate, menadione bisulfite) of photosystem I cyclic photophosphorylation activity. The rates of ATP synthesis obtained by this method (250–300 Μmol/h-mg chlorophyll) indicate that sulfonated quinones are efficient mediators of cyclic electron transport around photosystem I. Although the activity catalyzed by these compounds is highly sensitive to dibromothymoquinone, very little decrease in activity is observed with antimycin A.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71689/1/j.1751-1097.1979.tb09271.x.pd