Photosystem-II-enriched membrane fragments obtained by detergent solubilisation of thylakoid membranes were found to contain almost exclusively the high redox potential form of cytochrome b-559 (Em,6.0 = + 353 mV), provided that the haem was maintained in the reduced state during the isolation procedure. A reducing potential was required during the isolation due to the instability of the oxidised form of the high-potential couple. Additional detergent treatment of such preparations converted all of the cytochrome to a low potential form (Em,6.0 of around + 100 mV). Dissociation of the 23 kDa extrinsic polypeptide, bound at the lumenal side of Photosystem II, had no effect on the redox state of the cytochrome provided that calcium remained in association with the Photosystem II complex. Removal of the 33 kDa extrinsic protein, in addition to the 23 kDa, resulted in the conversion of the haem to an intermediate (Em,6.0 = + 169 mV) redox form, independent of the presence of calcium. Considering that these preparations are derived from the granal regions of the thylakoid membranes, the data suggest that, in vivo, Photosystem II complexes in these regions contain only the high redox potential form of the cytochrome. The data further suggest that, in addition to the 33 kDa protein, ligation of calcium rather than the 23 kDa polypeptide is required for the stabilisation of this form of cytochrome b-559. © 1995.
McNamara, V. P., & Gounaris, K. (1995). Granal photosystem II complexes contain only the high redox potential form of cytochrome b-559 which is stabilised by the ligation of calcium. BBA - Bioenergetics, 1231(3), 289–296. https://doi.org/10.1016/0005-2728(95)00093-X