Amino acid sequence of 10-kDa protein in photosystem I reaction-center complex from a thermophilic cyanobacterium, Synechococcus elongatus Naegeli.

Four small subunits (14, 13, 10, and 8 kDa) of the photosystem I reaction-center complex were isolated from a thermophilic cyanobacterium Synechococcus elongatus. The complete amino acid sequence of the 10-kDa subunit was determined to consist of 80 amino acid residues giving a molecular mass of 8855.3, excluding iron and sulfur atoms, and containing two special sequences of cysteine residues, Cys-X-X-Cys-X-X-Cys-X-X-X-Cys-Pro, at residues 10-21 and 47-58, which indicates that the subunit is an apoprotein carrying two iron-sulfur centers, FA and FB, assigned as [4Fe-4S] clusters. The amino acid sequence indicated an 87.5% identity compared with those deduced from the nucleotide sequences of chloroplast gene psa C from several plants.