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

Abstract: The interaction of La3+ and Tb3+ 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 Ca2+ cations. The feature of lanthanides to bind strongly to the Ca-binding site was used to investigate whether the bound Ln3+ 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 La3+ or Tb3+, and the activity of the high-affinity site was then examined using exogenous electron donors (Mn2+ + H2O2) 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. © 2023, Pleiades Publishing, Inc.