Lockett, Christopher John; (1990) Study on the role of calcium in photosynthetic oxygen evolution. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Three extrinsic polypeptides of molecular mass 17, 23, 33 kDa and 4 manganese ions associated with photosystem II are involved in the oxygen evolution process. Calcium and chloride ions are essential for oxygen evolution. If the 17 and 23 kDa polypeptides are depleted, mM concentrations of both ions have to be supplied for maximum oxygen evolution. The depletion of calcium ions from preparations of oxygen evolving photosystem 2 was investigated. Calcium ions were found to be accessible to depletion when the 17 and 23 kDa polypeptides were depleted. Calcium depletion was monitored by observing the S2 state multiline epr signal and measuring the rate of oxygen evolution. Calcium appeared to play an essential role in oxygen evolution. Strontium and vanadyl ions were the only divalent cations that partially replaced the role of calcium. When calcium ions were depleted in the S0 state there was no formation of the S2 state multiline epr signal and oxygen evolution was inhibited. Other calcium depletion methods inhibited oxygen evolution, but did not inhibit the formation of the S2 state multiline epr signal. The role of the tyrosine D in oxygen evolution and the effect of calcium depletion on this component was investigated. D was found to have a role in reseting the oxygen evolving complex to the S1 state in the dark. This did not occur after calcium depletion in the S0 state.

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