Comparative study of effects of artificial electron donors on the AT-band of photosystem II thermoluminescence.
Extraction of the Mn-cluster from photosystem II (PS II) inhibits the main bands of thermoluminescence and induces a new AT-band at -20 degrees 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.
Kultisheva
M Y
MY
School of Biology, Lomonosov Moscow State University, Moscow, 119899, Russia. kulticheva@mars.biophys.msu.ru
Lovyagina
E R
ER
Kuznetsov
A M
AM
Solntsev
M K
MK
Semin
B K
BK
Ivanov
I I
II
D015086:2,6-Dichloroindophenol / Q000378:metabolism* / Q000494:pharmacology; D001665:Binding Sites; D004160:Diphenylcarbazide / Q000378:metabolism* / Q000494:pharmacology; D004579:Electron Transport; D007501:Iron / Q000378:metabolism* / Q000494:pharmacology; D008027:Light; D008345:Manganese / Q000378:metabolism* / Q000494:pharmacology; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins / Q000187:drug effects / Q000378:metabolism*; D045332:Photosystem II Protein Complex; D018724:Spinacia oleracea / Q000378:metabolism; D013819:Thermoluminescent Dosimetry
D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D004160:Diphenylcarbazide; D008345:Manganese; D015086:2,6-Dichloroindophenol; D007501:Iron