Reconstruction of the Water‐Oxidizing Complex in Manganese‐Depleted Photosystem II Preparations Using Mononuclear Manganese Complexes

Abstract

The water-oxidizing complex of chloroplast photosystem I1 is composed of a cluster of four manganese atoms that can accumulate four oxidizing redox equivalents. Depletion of manganese from the water-oxidizing complex fully inhibits oxygen evolution. However, the complex can be reconstituted in the presence of exogenous manganese in a process called photoactivation. In the present study, mononuclear manganese complexes with ligands derived from either nitrosonaphthol and ethylenediamine (Niten) or from diaminohexane and salicylaldehyde (Salhxn) are used in photoactivation experiments. Measurements of photoinduced changes of chlorophyll fluorescence yield, thermal dissipation using photoacoustic spectroscopy, photoreduction of 2,6-dichorophenolindophenol and oxygen evolution in manganese-depleted and in reconstituted photosystem I1 preparations demonstrate that photoactivation is more efficient when Niten and Salhxn complexes are used instead of MnCI,. It is inferred that the aromatic ligands facilitate the interaction of the manganese atoms with photosystem 11. The addition of CaCI, and of the extrinsic polypeptide of 33 kDa known as the manganese-stabilizing protein during photoactivation further enhances the recovery of electron transport and oxygen evolution activities. It is proposed that mononuclear manganese complexes are able to contribute to reconstitution of the water-oxidizing complex by sequential addition of single ions similarly to the current model for assembly of the tetranuclear manganese cluster and that these complexes constitute suitable model systems to study the assembly of the water-oxidizing complex.

Reconstitution of the water-oxidizing complex in manganese-depleted photosystem II preparations using synthetic Mn complexes: a fluorine-19 NMR study of the reconstitution process

“…Such an effect of EDTA was not observed in our previous reconstitution studies with Mn complexes (Allakhverdiev et al 1994a, b;1999). The difference can be attributed to the higher stability of these complexes than the present complexes against ligand exchange.…”

“…In the reconstitution studies of the Mn-depleted PSII particles with synthetic Mn complexes, high rates of oxygen evolution were achieved by use of mononuclear complexes with Schiff-base ligands (Allakhverdiev et al 1999) and dinuclear complexes with naphthoquinone-oxime ligands (Allakhverdiev et al 1994a, b). One common feature of these Mn complexes and the complexes in this study is the presence of a large hydrophobic ligand.…”

Biphasic regulation of superoxide radical levels in Mn-depleted and photoactivated photosystem II

“…Attempt to increase the MnCl 2 concentrations did not lead to higher OEA (data not shown). As reported previously, the relatively low OEA in the photoactivation process using MnCl 2 could be improved by using the synthesized Mn complexes (Liu et al 2006, Allakhverdiev et al 1999.…”

Reconstitution of the water-oxidizing complex in manganese-depleted photosystem II preparations using synthetic binuclear Mn(II) and Mn(IV) complexes: production of hydrogen peroxide

“…1 The synthetic dinuclear manganese complexes used in this study as previously described (Klimov et al 1982;Allakhverdiev et al 1994aAllakhverdiev et al , b, 1997Allakhverdiev et al , 1999. Mn-depleted PSII membranes, suspended in buffer containing 300 mM sucrose, 50 mM NaCl, 100 lM NaHCO 3 , and 50 mM MES/NaOH buffer (pH 6.5) and in the presence of 0.5 mM K 3 Fe(CN) 6 , as the terminal electron acceptor at a chlorophyll concentration of 0.25 mg/ml, were preincubated with the Mn source (MnCl 2 or the binuclear complexes), CaCl 2 , and extrinsic proteins or were mixed, loaded into the photoactivation cell, and incubated in darkness at 4°C for 15 min prior to the start of the illumination.…”

“…Many of these complexes contain binuclear, trinuclear, or tetranuclear manganese centers. It therefore appeared interesting to use synthetic binuclear manganese complexes for reconstitution of the Mn-depleted PSII, and to examine their effects on the restoration of the oxygen evolution capacity (Allakhverdiev et al 1994a(Allakhverdiev et al , 1999.…”