Isolation and characterization of the 47 kDa protein and the D1-D2-cytochrome b-559 complex

The 47 kDa polypeptide and a protein complex consisting of the D1 (32 kDa), D2 (34 kDa) and cytochrome b-559 (9 kDa) species were isolated from a Tris-washed Photosystem II core complex solubilized with dodecylmaltoside in the presence of LiClO4. Although the 43 kDa chlorophyll-binding protein is readily dissociated from the Photosystem II complex under our conditions, two cycles of exposure to high concentrations of detergent and LiClO4 were required for complete removal of the 47 kDa chlorophyll-binding protein from the D1-D2-cytochrome b-559 complex. Spectroscopic characterization of these two species revealed that the 47 kDa protein binds chlorophyll a, whereas the D1-D2-cytochrome b-559 complex shows an enrichment in Pheo a and heme on a chlorophyll basis. A spin-polarized EPR triplet can be observed at liquid helium temperatures in the D1-D2-cytochrome b-559 complex, but no such triplet is observed in the purified 47 kDa species. The zero-field splitting parameters of the P-680+ triplet indicate that the triplet spin is localized onto one chlorophyll molecule. Resonance Raman spectroscopy showed that: (i) beta-carotene is bound to the reaction center in its all-trans conformation; (ii) all chlorophyll a molecules are five-coordinate; and (iii) the C-9 keto group of one of the chlorine pigments is hydrogen-bonded. Our results support the proposal that the D1-D2 complex binds the P-680+ and Pheo a species that are involved in the primary charge separation.