The 8 kDa polypeptide in photosystem I is a probable candidate of an iron‐sulfur center protein coded by the chloroplast gene frxA

The N‐terminal sequence of the 8 kDa polypeptide isolated from spinach photosystem I (PS I) particles was determined by a gas‐phase sequencer. The sequence showed the characteristic distribution of cysteine residues in the bacterial‐type ferredoxins and was highly homologous to that deduced from the chloroplast gene frxA of liverwort, Marchantia polymorpha. It is strongly suggested that the 8 kDa polypeptide has to be an apoprotein of one of the iron‐sulfur center proteins in PS I particles.