ESR spectroscopy demonstrates that cytochrome b559 remains low potential in Ca2+-reactivated, salt-washed PSII particles

Abstract

Cytochrome b₅₅₉ 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 b₅₅₉ 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 b₅₅₉, 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 b₅₅₉ 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 b₅₅₉ to lower potential form(s); addition of CaCl₂ reconstituted oxygen evolution activity but did not restore cyt b₅₅₉ to its high potential form(s).