. "Protein which contains at least one 4Fe-4S iron-sulfur cluster: 4 iron atoms complexed to 4 inorganic sulfides and 4 sulfur atoms of cysteines from the protein. In a number of iron-sulfur proteins, the 4Fe-4S cluster can be reversibly converted by oxidation and loss of one iron ion to a 3Fe-4S cluster." . . . "4Fe-4S" . . .