Schroder WP, Arellano JB, Bittner T, Baron M, Eckert HJ, Renger G
Flash-Induced Absorption-Spectroscopy Studies of Copper Interaction with Photosystem-Ii in Higher-Plants
Journal of Biological Chemistry: 1994 269:32865-32870
Measurements of flash-induced absorption changes at 325, 436, and 830 nm and of oxygen evolution were performed in order to analyze in detail the inhibition of photosystem II (PS II) by Cu(II) in PS II membrane fragments from spinach. (a) The kinetics of P680(+) reduction become markedly slower in the presence of 100 mu M CuSO4. (b) The CuSO4-induced kinetics of P680(+) reduction are dominated by a 140-160-mu s decay, (c) The extent of these 140-160-mu s kinetics, normalized to the overall decay, remains virtually unaffected by addition of the exogenous PS II donor, NH2OH. (d) In thoroughly dark-adapted samples the CuSO4-induced 140-160-mu s kinetics are already observed after the first flash and remain unchanged by a train of excitation flashes. (e) The extent of P680(+) and Q(A)(-) formation under repetitive flash excitation is not diminished by addition of 100 mu M CuSO4. (f) The induction of mu s kinetics of P680(+) reduction at the expense of ns kinetics and the inhibition of the saturation rate of oxygen evolution exhibit the same dependence on CuSO4 concentration, (g) CuSO4 also transforms the 10-20-mu s reduction of P680(+) by Tyr(Z) in Tris-washed PS II membrane fragments into 140-160-mu s kinetics without any effect on the extent of flash-induced P680(+) formation. These results unambiguously show that Cu(II) does not affect the charge separation (P680(+)Q(A)(-)), but instead specifically modifies Tyr(Z) and/or its micro environment so that the electron transfer to P680(+) becomes blocked.
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