20.10 With the last step of the S cycle having a characteristic time of
1 ms, the rate of oxygen production could proceed at a rate of
1000 molecules per second.20.11 The high potential allows P680 to perform more redox reactions,
including the oxidation of water.20.12 A higher oxidation/reduction potential is achieved by changing the
protein environment to make the surroundings favor the ground
state. This can be achieved by increasing the hydrophobicity or by
introducing positively charged amino acid residues.20.13 Tyrosine serves as an intermediate electron donor between P680+
and the manganese cluster and as a participant in the associated
proton-transfer processes.20.14 The manganese ions are highly interacting and in a suitable oxida-
tion state.20.15The oxidation states of the manganese cluster change in the S states.20.16 The number of lines can vary depending on the configuration and
potentially there could be many more than observed. Given the
observed spectrum, there are many allowed configurations.20.17 It predicts that each step is associated with the transfer of one proton.20.18 Many answers are possible.20.19 He saw the longed-lived state of photosystem II arising from an
oxidized tyrosine.ANSWERS TO PROBLEMS 487
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