High-resolution triplet-minus-singlet absorbance difference spectrum of photosystem II particles

AbstractThe triplet state of the primary donor of photosystem II particles prepared from a mutant of Chlamydomonas reinhardtii has been studied at 1.2 K with absorbance-detected ESR in zero-magnetic field (ADMR). Two sets of resonances with slightly different zero-field splitting parameters |D| and |E| were observed, |D| = 285.5, |E| = 38.8 and |D| = 288.8 × 10−4 cm−1, |E| = 42.2 × 10−4 cm−1, respectively. Both sets of |D| and |E| values are close to those found for PT-700, as are the sublevel decay rates kx = 930 ± 40, ky = 1088 ± 50 and kz = 110 ± 5 s−1. The AMDR-detected triplet-minus-singlet absorbance difference spectrum of PT-680 is very similar to that of PT-700 and closely resembles that of covalently connected Chl a dimers in vitro. We conclude that P-680 is a Chl a dimer whose general structure is similar to that of P-700