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Comparative Study of Effects of Artificial Electron Donors on the AT-Band of Photosystem II Thermoluminescence

M. Yu. Kultisheva1*, E. R. Lovyagina1, A. M. Kuznetsov2, M. K. Solntsev2, B. K. Semin1, and I. I. Ivanov1

1School of Biology, Lomonosov Moscow State University, Moscow, 119899 Russia; fax: (095) 939-1115; E-mail: kulticheva@mars.biophys.msu.ru; loviagina@mars.biophys.msu.ru; semin@mars.biophys.msu.ru; ivanov@mars.biophys.msu.ru

2School of Physics, Lomonosov Moscow State University, Moscow, 119899 Russia; fax: (095) 939-1195; E-mail: mks@bio471c.phys.msu.ru

* To whom correspondence should be addressed.

Received December 22, 2000; Revision received March 2, 2001
Extraction of the Mn-cluster from photosystem II (PS II) inhibits the main bands of thermoluminescence and induces a new AT-band at -20°C. This band is attributed to the charge recombination between acceptor QA- and a redox-active histidine residue on the donor side of PS II. The effect of Mn(II) and Fe(II) cations as well as the artificial donors diphenylcarbazide and hydroxylamine on the AT-band of thermoluminescence was studied to elucidate the role of the redox-active His residue in binding to the Mn(II) and Fe(II). At the Mn/PS II reaction center (RC) ratio of 90 : 1 and Fe/PS II RC ratio of 120 : 1, treatment with Mn(II) and Fe(II) causes only 60% inhibition of the AT-band. Preliminary exposure of Mn-depleted PS II preparations to light in the presence of Mn(II) and Fe(II) causes binding of the cations to the high-affinity Mn-binding site, thereby inhibiting oxidation of the His residue involved in the AT-band formation. The efficiency of the AT-band quenching induced by diphenylcarbazide and hydroxylamine is almost an order of magnitude higher than the quenching efficiency of Mn(II) and Fe(II). Our results suggest that the redox-active His is not a ligand of the high-affinity site and does not participate in the electron transport from Mn(II) and Fe(II) to YZ. The concentration dependences of the AT-band inhibition by Mn(II) and Fe(II) coincide with each other, thereby implying specific interaction of Fe(II) with the donor side of PS II.
KEY WORDS: photosynthesis, photosystem II, water-oxidizing complex, manganese cluster, iron, thermoluminescence