Interaction of Zn2+ with the donor side of Photosystem II

Abstract

The inhibitory effect of Zn(2+) on photosynthetic electron transport was investigated in native and CaCl2-treated (depleted in extrinsic polypeptides) Photosystem II (PS II) submembrane preparations. Inhibition of 2,6-dichlorophenolindophenol photoreduction by Zn(2+) was much stronger in protein-depleted preparations in comparison to the native form. It was found that Ca(2+) significantly reduced the inhibition in the native PS II preparations, as did Mn(2+) in a combination with H2O2 in the protein-depleted counterparts. No other tested monovalent or divalent cations could replace Ca(2+) or Mn(2+) in the respective experiments. Diphenylcarbazide could partially relieve (40-45%) the inhibition in both types of preparations. The above indicates the presence of an active Zn(2+) inhibitory site on the donor side of PS II. However, neither Ca(2+) nor Mn(2+) could completely prevent inhibition by high concentrations of Zn(2+) (>1 mM). We propose that elevated levels of Zn(2+) strongly perturb the conformation of the PS II core complex and might also affect the acceptor side of the photosystem.

The Conserved His-144 in the PsbP Protein Is Important for the Interaction between the PsbP N-terminus and the Cyt b559 Subunit of Photosystem II

“…It was reported that a low concentration of Zn 2ϩ (ϳ2 mM) inhibited the activity of PSII and caused dissociation of PsbP and PsbQ from the core complex in spinach PSII (39,40). Presumably, the Zn 2ϩ incorporated into PsbP would hinder proper interaction between the His-144 and Asp-165 residues, and interfere with the function of PsbP.…”

The action of mercury on the binding of the extrinsic polypeptides associated with the water oxidizing complex of photosystem II

“…PSII submembrane fractions were isolated from barley (Hordeum vulgarae) according to [5] and from spinach (Spinacia oleracea L.) according to [6] with the modifications described previously [7]. The PSII preparations were finally resuspended in 400 mM sucrose and 20 mM MES-TMAOH pH 6.3 and were stored in liquid nitrogen until use.…”

Molecular mechanism of action of Pb2+ and Zn2+ on water oxidizing complex of photosystem II

“…At least three inorganic cofactors, CI-, Ca 2+ and Mn 2+, are reported to be associated with these polypeptides (see reviews by [5,6,7,8]). By using detergent-derived PSII membrane fractions, in which the donor side is exposed to outer environment [9], it was shown that Pb z+ competitively inhibited Ca 2+ and C1-binding [10], and Zn 2+ non-competitively inhibited Ca 2+ and Mn 2+ binding [11] at native sites on water oxidase. From these studies, it was concluded that Pb 2+ or Zn2+-induced inhibition of photosystem II activity was mediated by the loss of specific inorganic cofactors, necessary for water oxidation [10,11].…”