Evidence for the role of a bound ferredoxin as the primary electron acceptor of Photosystem I in spinach chloroplasts

The presence of a bound electron transport component in spinach chloroplasts with an EPR spectrum characteristic of a ferredoxin has been confirmed. The ferredoxin is photoreduced at 77 °K or at room temperature, it is not reduced in the dark by Na₂S₂O₄. The distribution of the ferredoxin in subchloroplast particles has been investigated. The ferredoxin is enriched in Photosystem I particles and it is proposed that it functions as primary electron acceptor for Photosystem I.

The EPR spectra indicate the presence of two components which are photoreduced sequentially. It is proposed that they may represent two active centres of a single protein.