Logistics in the life cycle of Photosystem IIlateral movement in the thylakoid membrane and activation of electron transfer

• Due to its unique ability to split water, Photosystem II (PSII) is easily accessible to oxidative damage. Photoinhibited PSII centres diffuse laterally from the grana core region of the thylakoid membrane to the stroma lamellae in order to allow replacement of damaged proteins and cofactors. The 'new born' PSII centres in this region are characterized by the absence of the water splitting capacity and very poor ability to bind the secondary quinone acceptor, QB. After the repair process PSII has to regain the water splitting capacity. This requires a set of well-defined electron transfer reactions leading to assembly of the Mn-cluster. In order to minimize the danger of photoinhibition during these earlier stages of photoactivation of PSII, auxiliary donors to the primary donor P680+, such as redox active tyrosine on D2 protein, YD, and cytochrome b559 become involved in the electron transport reactions by providing necessary electrons. Cytochrome b559 may also serve as an electron acceptor to QA if elevated light intensities occur during the photoactivation process. These reactions lead to activation of QB binding, and finally to the assembly of the Mn-cluster. All these electron transport events occur simultaneously with the lateral movement of PSII centres back to the appressed regions of the grana core, where the pool of the most active PSII is situated.

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NATURVETENSKAP  -- Biologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences (hsv//eng)

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