In seeking a useful model to simulate some aspects of cytochrome P-450 reduction, acetylated cytochrome c was used as an electron acceptor for the NADPH-dependent adrenodoxin reductase plus adrenodoxin system. The modified cytochrome accepts electrons both directly from adrenodoxin and indirectly via superoxide anion. The rate of reduction of native cytochrome c increases linearly as the ratio of adrenodoxin to adrenodoxin reductase is increased, up to a maximal ratio of 1:1, above which the activity does not change. In contrast, little activity in acetylated cytochrome c reduction is seen at a 1:1 ratio of adrenodoxin to reductase, and activity is seen only as this ratio is exceeded, thus creating a lag in the adrenodoxin activity titration. Reduction of native cytochrome c is inhibited only at the high salt concentrations which lead to dissociation of the 1:1 adrenodoxin reductase-adrenodoxin complex. Similarly, reduction of acetylated cytochrome c is inhibited by high salt, but activity is also inhibited at low salt concentration. Acetylated cytochrome c thus provides an excellent model electron acceptor for steroidogenic electron transport, and studies support the role of adrenodoxin as a mobile electron shuttle between adrenodoxin reductase and a hemoprotein electron acceptor (either acetylated cytochrome c or cytochrome(s) P-450).