Electrometrical study of electron transfer from the terminal F-A/F-B iron-sulfur clusters to external acceptors in photosystem I

An electrometrical technique was used to investigate electron transfer betw een the terminal iron-sulfur centers F-A/F-B and external electron accepter s in photosystem I(PS I) complexes from the cyanobacterium Synechococcus sp , PCC 6301 and from spinach, The increase of the relative contribution of t he slow components of the membrane potential decay kinetics in the presence of both native (ferredoxin, flavodoxin) and artificial (methyl viologen) e lectron accepters indicate the effective interaction between the terminal [ 4Fe-4S] cluster and accepters. The finding that F-A fails to donate electro ns to flavodoxin in F-B-less (HgCl2-treated) PS I complexes suggests that F -B is the direct electron donor to flavodoxin, The lack of additional elect rogenicity under conditions of effective electron transfer from the F-B red ox center to soluble accepters indicates that this reaction is electrically silent. (C) 1999 Federation of European Biochemical Societies.