The S1 split signal of photosystem II; a tyrosine–manganese coupled interaction

Detailed optical and EPR analyses of states induced in dark-adapted PS II membranes by cryogenic illumination permit characterization and quantification of all pigment derived donors and acceptors, as well as optically silent (in the visible, near infrared) species which are EPR active. Near complete turnover formation of QA− is seen in all centers, but with variable efficiency, depending on the donor species. In minimally detergent-exposed PS II membranes, negligible (< 5%) oxidation of chlorophyll or carotenoid centers occurs for illumination temperatures 5–20 K. An optically silent electron donor to P680+ is observed with the same decay kinetics as the S1 split signal. Cryogenic donors to P680+ seen are: (i) transient (t1/2 ∼ 150 s) tyrosine related species, including ‘split signals’ (∼ 15% total centers), (ii) reduced cytochrome b559 (∼ 30–50% centers), and (iii) an organic donor, possibly an amino acid side chain, (∼ 30% centers).