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  • Substrate water exchange in photosystem II core complexes of the extremophilic red alga Cyanidioschyzon merolae.

Substrate water exchange in photosystem II core complexes of the extremophilic red alga Cyanidioschyzon merolae.

Biochimica et biophysica acta (2014-04-15)
Håkan Nilsson, Tomasz Krupnik, Joanna Kargul, Johannes Messinger
ABSTRACT

The binding affinity of the two substrate-water molecules to the water-oxidizing Mn₄CaO₅ catalyst in photosystem II core complexes of the extremophilic red alga Cyanidioschyzon merolae was studied in the S₂ and S₃ states by the exchange of bound ¹⁶O-substrate against ¹⁸O-labeled water. The rate of this exchange was detected via the membrane-inlet mass spectrometric analysis of flash-induced oxygen evolution. For both redox states a fast and slow phase of water-exchange was resolved at the mixed labeled m/z 34 mass peak: kf=52 ± 8s⁻¹ and ks=1.9 ± 0.3s⁻¹ in the S₂ state, and kf=42 ± 2s⁻¹ and kslow=1.2 ± 0.3s⁻¹ in S₃, respectively. Overall these exchange rates are similar to those observed previously with preparations of other organisms. The most remarkable finding is a significantly slower exchange at the fast substrate-water site in the S₂ state, which confirms beyond doubt that both substrate-water molecules are already bound in the S2 state. This leads to a very small change of the affinity for both the fast and the slowly exchanging substrates during the S₂→S₃ transition. Implications for recent models for water-oxidation are briefly discussed.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Manganese, powder, ≥99.9% trace metals basis
Sigma-Aldrich
Manganese, chips, thickness <2.0 mm, 99%
Sigma-Aldrich
Manganese, powder, −325 mesh, ≥99% trace metals basis
Manganese, foil, not light tested, 25x25mm, thickness 0.015mm, permanent polyester support, 98.7%
Manganese, foil, not light tested, 25x25mm, thickness 0.02mm, permanent polyester support, 98.7%
Manganese, foil, not light tested, 50x50mm, thickness 0.002mm, permanent polyester support, 98.7%
Manganese, foil, not light tested, 50x50mm, thickness 0.0025mm, permanent polyester support, 98.7%
Manganese, foil, not light tested, 25x25mm, thickness 0.0025mm, permanent polyester support, 98.7%
Manganese, foil, not light tested, 50x50mm, thickness 0.01mm, permanent polyester support, 98.7%
Manganese, foil, not light tested, 25x25mm, thickness 0.006mm, permanent polyester support, 98.7%
Manganese, foil, not light tested, 25x25mm, thickness 0.01mm, permanent polyester support, 98.7%
Manganese, foil, not light tested, 50x50mm, thickness 0.015mm, permanent polyester support, 98.7%
Manganese, foil, not light tested, 50x50mm, thickness 0.003mm, permanent polyester support, 98.7%
Manganese, foil, not light tested, 25x25mm, thickness 0.007mm, permanent polyester support, 98.7%
Manganese, foil, not light tested, 50x50mm, thickness 0.004mm, permanent polyester support, 98.7%
Manganese, foil, not light tested, 25x25mm, thickness 0.008mm, permanent polyester support, 98.7%
Manganese, foil, 25x25mm, thickness 2mm, hot-pressed, 99.95%
Manganese, rod, 50mm, diameter 6.35mm, cast, 99.5%
Manganese, foil, not light tested, 50x50mm, thickness 0.0125mm, permanent polyester support, 98.7%
Manganese, foil, not light tested, 50x50mm, thickness 0.025mm, permanent polyester support, 98.7%
Manganese, foil, not light tested, 25x25mm, thickness 0.004mm, permanent polyester support, 98.7%
Manganese, foil, not light tested, 50x50mm, thickness 0.001mm, permanent polyester support, 98.7%
Manganese, foil, not light tested, 25x25mm, thickness 0.009mm, permanent polyester support, 98.7%
Manganese, foil, 50x50mm, thickness 2mm, hot-pressed, 99.95%
Manganese, foil, not light tested, 50x50mm, thickness 0.02mm, permanent polyester support, 98.7%
Manganese, foil, not light tested, 50x50mm, thickness 0.006mm, permanent polyester support, 98.7%
Manganese, foil, not light tested, 25x25mm, thickness 0.001mm, permanent polyester support, 98.7%
Manganese, rod, 10mm, diameter 4.0mm, cast, 99.5%
Manganese, foil, not light tested, 50x50mm, thickness 0.007mm, permanent polyester support, 98.7%
Manganese, foil, not light tested, 50x50mm, thickness 0.005mm, permanent polyester support, 98.7%