The samples used in these experiments were prepared by J. Dekker and collaborators (Dekker et al. 1989, 1990; Eijckelhoff and Dekker 1995; Kwa et al. 1992). They were subsequently diluted in buffer and glycerol to work at low temperature (Den Hartog et al. 1998b). The SD behaviour of the PSII sub-core complexes is compared here with that of B777, the monomer subunit of the LH1 complex of purple bacteria. B777 was obtained from LH1 by adding the detergent n-octyl-β-glucopiranoside (OG) and diluted in buffer and glycerol (Creemers et al. 1999a, and references therein). The B777 complex, in turn, is compared with BChl a embedded

in the same OG detergent (diluted in buffer and glycerol) without the protein, which we call here BChl a in OG-glass (Creemers and Völker 2000). The purpose of this experiment was two-fold, to compare the SD behaviour this website of proteins with that of glasses, and to clear up a long-standing problem: whether the BTK inhibitor chemical structure BChl a molecule in B777 is bound or not to the protein (Sturgis and Robert 1994, and references therein). HB results on SD of B820, the dimer subunit of LH1, at various temperatures and delay

times, and its comparison to glasses, can be found in Störkel et al. (1998). Photosystem II (PSII), the ‘engine of life’, is a large complex embedded in the thylakoid membranes of plants, algae and cyanobacteria. Driven ifenprodil by solar energy, PSII catalyzes the splitting of water into oxygen which is essential for the survival of life on Earth (for a review, see Barber 2008). The events that give rise to the primary and secondary electron-transfer processes, which lead to water oxidation start with the absorption of sunlight by a peripheral light-harvesting complex, called LHCII (Kühlbrandt et al. 1994),

which transfers the excitation energy to the RC within the PSII core complex. The isolated PSII RC, which is the smallest unit that shows photochemical activity (Nanba and Satoh 1987; Rhee et al. 1997), is composed of the D1 and D2 proteins and bound mainly to the CP43 and CP47 complexes (Boekema et al. 1998; Dekker and Boekema 2005). The D1 and D2 proteins contain the cofactors that bring about charge separation. The crystal structures of cyanobacterial PSII, determined by X-ray crystallography at 3.5 Å (Ferreira et al. 2004) and 3 Å (Loll et al. 2005) resolution, confirmed the dimeric organization of the isolated complex and the positioning of the major subunits within each monomer, previously obtained by electron crystallography (Eijckelhoff et al. 1997; Rhee et al. 1997). Loll et al. (2005) concluded that there are about 36 Chl a and 11 β-carotene molecules per PSII core, and that the CP43 and CP47 complexes bind 13 and 16 Chls, respectively, while the RC binds 6 Chls, 2 pheophytin (Pheo) molecules, 2 plastoquinone (PQ) molecules, at least one β-carotene and a non-heme Fe.