F_A/F_B Protein from the Spinach Photosystem I Complex: Isolation in a Native State and Some Properties of the Iron-Sulfur Clusters

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The F_A/F_B Protein of the photosystem I complex was isolated from spinach leaves in a native state by use of anaerobic systems. The protein contained 8.5 non-heme iron atoms and 8.0 acid-labile sulfur atoms per molecule, consistent with the current concept that it has two [4Fe-4S] clusters. Its absorption spectrum was very similar to those of bacterial-type ferredoxins. The ratio of the absorbance at 390 nm to that at 280 nm was 0.6, and the molar extinction coefficient at 390 nm was 32,000 M^<-1>.cm^<-1>. The oxidation-reduction properties of the iron-sulfur clusters were examined by redox potentiometry and EPR spectroscopy. The two clusters were distinguishable in terms of their oxidation-reduction midpoint potentials; their E_m values were determined to be about -470mV and -560mV, respectively.
日本植物生理学会の論文