<unk>  is an important component of Photosystem II.
PSII is a multisubunit protein-pigment complex containing polypeptides both intrinsic and extrinsic to the photosynthetic membrane. Within the core of the complex, the chlorophyll and beta-carotene pigments are mainly bound to the antenna proteins CP43 (PsbC) and CP47 (PsbB), which pass the excitation energy on to the reaction centre proteins D1 (Qb, PsbA) and D2 (Qa, PsbD) that bind all the redox-active cofactors involved in the energy conversion process. The PSII oxygen-evolving complex (OEC) oxidises water to provide protons for use by PSI, and consists of OEE1 (PsbO), OEE2 (PsbP) and OEE3 (PsbQ). The remaining subunits in PSII are of low molecular weight (less than 10 kDa), and are involved in PSII assembly, stabilisation, dimerisation, and photo-protection.<unk> , which forms part of the reaction centre core of PSII is a heterodimer composed of one alpha subunit (PsbE), one beta (PsbF) subunit, and a haem cofactor. Two histidine residues from each subunit coordinate the haem. Although<unk>  is a redox-active protein, it is unlikely to be involved in the primary electron transport in PSII due to its very slow photo-oxidation and photo-reduction kinetics. Instead,<unk>  could participate in a secondary electron transport pathway that helps protect PSII from photo-damage.<unk>  is essential for PSII assembly.
This domain occurs in both the alpha and beta subunits of<unk> . In the alpha sbunit it occurs together with a lumenal domain (InterPro: IPR013082), while in the beta subunit it occurs on its own.
Cytochrome b559
Cytochrome c oxidase
Ubiquinol oxidase
ATPase
Coenzyme Q - cytochrome c reductase
NADH dehydrogenase
Methaemoglobin
Nicotinamide adenine dinucleotide phosphate