Some Insight into Intramolecular Electron Transfer of an Adrenodoxin Molecule

Abstract

The question of whether or not an aromatic amino acid residue participates in the electron transfer reaction from the surface of protein molecule to the iron-sulfur cluster has been a subject of considerable interest and debate. In particular, heme and non-heme iron proteins have been extensively investigated by utilizing such varied approaches as chemical modification, comparison of the oxidized and reduced structures by means of X-ray crystallography, and kinetic pulse radiolysis studies. In bacterial ferredoxins, both 13-C nuclear magnetic resonance (1,2) and X-ray crystallography studies have revealed unequivocally the proximity of a tyrosine residue to the 4Fe-4S cluster. An elegant study by Rabinowitz’s group indicated that a modified ferredoxin from Clostridum M-E free of any aromatic residue is as active as the native ferredoxin from Clostridium acidi urici (5) in the phosphoroclastic reaction. They concluded that the aromatic residues do not participate in the intramolecular electron transfer reaction in the bacterial ferredoxin.