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A high-potential redox component located within cyanobacterial Photosystem II
Authors:Richard G. Piccioni  David C. Mauzerall  
Affiliation:

The Rockefeller University, New York, N.Y. 10021, U.S.A.

Abstract:The calcium-dependent oxygen evolution activity of preparations of Phormidium luridum shows a marked selectivity in favor of ferricyanide over benzoquinone as Hill oxidant. In addition, the rate of oxygen evolution increases with increasing solution redox potential over the range +350 to +550 mV vs. the standard hydrogen electrode. These properties pertain to both 3-(3,4-dichlorophenyl)-1,1-dimethylurea-sensitive and -insensitive fractions of the total oxygen evolution activity. Neither changes in solution potential nor use of oxidants other than ferricyanide obviate the need for added Ca2+.

To explain these observations, two models are proposed, each of which invokes the existence of a redox component located within Photosystem II and having a midpoint potential greater than +450 mV. In one model, the postulated species is a donor which competes with water for oxidizing equivalents generated by System II. In the other model, the 450 mV species is a high-potential primary acceptor of System II electrons.

Keywords:DCMU, 3-(3,4-dichlorophenyl)-1,1-dimethylurea  To whom reprint requests should be sent.
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