Comparative study of effects of artificial electron donors on the AT-band of photosystem II thermoluminescence

• Published in: Biochemistry (Moscow) 2001-07, Vol.66 (7), p.715
• Main Authors: Kultisheva, M Y, Lovyagina, E R, Kuznetsov, A M, Solntsev, M K, Semin, B K, Ivanov, I I
• Format: Article
• Language: English
• Subjects: 2,6-Dichloroindophenol - metabolism; 2,6-Dichloroindophenol - pharmacology; Binding Sites; Cations; Comparative studies; Diphenylcarbazide - metabolism; Diphenylcarbazide - pharmacology; Electron Transport; Iron - metabolism; Iron - pharmacology; Light; Manganese - metabolism; Manganese - pharmacology; Oxidation-Reduction; Photosynthetic Reaction Center Complex Proteins - drug effects; Photosynthetic Reaction Center Complex Proteins - metabolism; Photosystem II Protein Complex; Spinacia oleracea - metabolism; Thermoluminescence; Thermoluminescent Dosimetry
• ISSN: 0006-2979; 1608-3040
• DOI: 10.1023/A:1010248309383

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.