The possible role of aromatic residues of Clostridium acidi-urici ferredoxin in electron transport.

The (13)C-resonances of the 2',6'-ring carbon atoms of both tyrosyl residues of Clostridium acidi-urici ferredoxin are shifted downfield in the oxidized and reduced protein relative to these resonance positions in free tyrosine. These results show that both tyrosyl residues in the oxidized and reduced protein are in magnetically equivalent environments, and suggest that both tyrosyl residues are close to the two iron-sulfur clusters in the reduced and oxidized proteins and that each cluster is equally accessible to one reducing electron.