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

摘要

The FA/FBprotein 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−.cm−.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 Emvalues were determined to be about-470 mV and-560 mV, respectiv