Stark shifts and exciton coupling in PSII ‘Supercores’

Low-temperature spectroscopic measurements are reported on a detergent solubilized plant photosystem II (PSII) core preparation retaining full O2 evolving capacity but only 32 chlorophyll-aʹs (chla) per reaction center (RC). Absorption, CD, MCD and luminescence measurements in the S1 state allow the identification of the exciton splitting in P680 as 187 cm−1. Illumination converts PSII to the S2 state(s) and Stark shifts of individual PSII chromophores are identifiable. Stark shifts are analyzed in terms of structural details of PSII. The relationship of our results to the studies of preparations containing 4–6 chla per RC is outlined.