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Title: Characterisation of the Photosystem 2 reaction centre complex
Author: Demetriou, Christalla
Awarding Body: University of London
Current Institution: University College London (University of London)
Date of Award: 1990
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The reaction centre components of Photosystem II are bound to a heterodimer of the D1 and D2 polypeptides, in analogy with the L and M subunits of the bacterial reaction centre. This was confirmed with the isolation of a photochemically active complex consisting of the Dl/D2/cytochrome b559 polypeptides. The complex however does not contain bound quinone and is light and temperature labile. In this thesis, esr and laser flash spectroscopy were used to characterise the components of the reaction centre complex of higher plants. The isolation of the complex from a variety of organisms is also reported. Both si1icomolybdate (SiMo) and ferricyanide (FeCN) were shown to act as electron acceptors at cryogenic temperatures in the Dl/D2/cyt b559 complex. In the presence of either SiMo or FeCN, two radicals at g=2 were observed from P680+ (0.8mT) and the accessory monomeric chlorophyll (1.OmT). A radical attributed to tyrosine radical (D+/Z+) was also observed in a small number of centres. The complex was found to be more stable under anaerobic conditions. This suggests that photodamage of the complex may arise as a result of the reaction of the triplet form of chlorophyll with oxygen to form oxygen radicals. A possible role of cyt b559 in the prevention of photodamage is presented. The addition of exogenous quinone, in the form of decylplastoquinone, to the complex facilitated the reduction of cyt b559, although no evidence of specific binding was observed. However, experimental evidence of specific binding was obtained in the presence of the exogenous quinone, dibromothymoquinone.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available