Mechanism of Inhibition of the Oxygen-Evolving Complex of Photosystem II by Lanthanide Cations

• Published in: Biophysics (Oxford) 2023-08, Vol.68 (4), p.519-524
• Main Authors: Lovyagina, E. R., Loktyushkin, A. V., Vasiliev, N. S., Semin, B. K.
• Format: Article
• Language: English
• Subjects: Affinity; Binding sites; Biological and Medical Physics; Biophysics; Cell Biophysics; Hydrogen peroxide; Hydroquinone; Manganese; Oxygen; Photosystem II; Physics; Physics and Astronomy
• ISSN: 0006-3509; 1555-6654
• DOI: 10.1134/S0006350923040103

The interaction of La 3+ and Tb 3+ cations with the Ca-binding site of the oxygen-evolving complex of photosystem II samples depleted of calcium has been studied. The binding of cations to the Ca-binding site is irreversible and the bound cations cannot be washed out or replaced by Ca 2+ cations. The feature of lanthanides to bind strongly to the Ca-binding site was used to investigate whether the bound Ln 3+ cation has an effect on the high-affinity Mn-binding site of the oxygen-evolving complex. For this purpose, hydroquinone was used to extract manganese cations from the oxygen-evolving complex of the calcium-depleted photosystem II membranes with the Ca-binding site blocked by La 3+ or Tb 3+ , and the activity of the high-affinity site was then examined using exogenous electron donors (Mn 2+ + H 2 O 2 ) and 1,5-diphenylcarbazide. It was found that lanthanide cations bound to the Ca-binding site significantly inhibited oxidation of electron donors through the high-affinity Mn-binding site. The mechanism of the observed effect is discussed.