Abstract
Cytochrome (cyt) b559 is an essential component of photosystem (PS) II. Although cyt b559 is supposed to play a role for the protection of PS II from damage caused by excess light energy, its function remains unclear. The redox potentials of b-type cyt usually ranges from 0 to +100 mV (vs. SHE), while some researchers have reported using a chemical redox titration technique that cyt b559 exhibits a different redox potential around +400 mV. In the present study, to examine the redox property of cyt b559 precisely, we have tried to measure the redox potential of cyt b559 in D1/D2/cyt b559 reaction center complex isolated from spinach with a spectroelectrochemical technique. The redox potential of cyt b559 in the sample was +89.5 ± 3.0 mV (3 measurements). Furthermore, cyt b559 exhibited a one-electron redox reaction only at the potential in the range from 0 to +400 mV.
