RESUMEN
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 Q(A)((-)) 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 S(1) split signal. Cryogenic donors to P680(+) seen are: (i) transient (t(1/2) approximately 150 s) tyrosine related species, including 'split signals' ( approximately 15% total centers), (ii) reduced cytochrome b(559) ( approximately 30-50% centers), and (iii) an organic donor, possibly an amino acid side chain, ( approximately 30% centers).
