For both the [2Fe-2S] and the [4Fe-4S] ferredoxins, dialysis against 2H2O prior to single electron reduction leads to the appearance of a deuterium modulation pattern in the electron spin echo decay envelope indicative of deuteron-proton exchange very near the paramagnetic center. In contrast, if the ferredoxin is exposed to 2H2O after its reduction in H2O, far less deuterium exchange near the metal center takes place. Thus, proton exchange with solvent is in part dependent on the redox state of the protein. For high potential iron-sulfur proteins, this type of proton-deuteron exchange near the metal center does not occur unless the protein is partially unfolded in dimethylsulfoxide in 2H2O.

Reduction potentials were measured for P450 scc without bound steroid, complexed to the steroid substrate, intermediates and product of the cholesterol side chain cleavage reaction, and complexed to adrenodoxin. An investigation was also made of the stoichiometry of complexes in solution of the three proteins which carry out this reaction and of the rates of electron transfer between these proteins.