ESR spectroscopy demonstrates that cytochrome b 559 remains low potential in Ca 2+ -reactivated, salt-washed PSII particles

Abstract

Cytochrome b 559 in various Photosystem II preparations was studled by using low temperature ESR spectroscopy. This technique was used because it is able to distinguish high from low potential forms of the cytochrome owing to the g-value differences between these species. Moreover, by using low temperature irradiation to oxidize cyt b 559 we have avoided the use of redox mediators. Previous work (Ghanotakis DF., Topper J.N. and Yocum, C.F. (1984) Biochim. Biophys. Acta 767 , 524–531) demonstrated that reduction and extraction of manganese of the oxygen evolving complex, which might be expected to alter the redox properties of cyt b 559 , occurs when certain PSII preparations are exposed to reductants. The ESR data presented here show that a mixture of high potential and lower potential cyt b 559 species is observed in the oxygen evolving Photosystem II complex. Treatment of PSII membranes with 0.8 M Tris converts the high potential form(s) to those of lower potential. Exposure of the membranes to 2M NaCl shifts a significant amount of high potential cyt b 559 to lower potential form(s); addition of CaCl 2 reconstituted oxygen evolution activity but did not restore cyt b 559 to its high potential form(s).