Adrenodoxins and Their Role in the Cytochrome P450 Systems

Abstract—

The role of partner proteins in the formation of functional complexes in cytochrome P450 systems was investigated by means of the optical biosensor technique, used to determine kinetic constants and equilibrium dissociation constants of complexes of cytochrome CYP11A1 (P450scc) with wild-type adrenodoxin (Adx WT) and mutant forms of adrenodoxin R106D and D109R. Wild-type adrenodoxin (K_d = (1.23 ± 0.09) × 10^–6 M) and mutant D109R (K_d = (2.37 ± 0.09) × 10^–8 M) formed complexes with cytochrome P450scc. In the case of the R106D mutant, no complex formation was detected. The possibility of participation of adrenodoxins and their mutant variants in the process of electron transfer as electron donors in mitochondrial cytochrome P450 systems, was assessed studying the electrochemical properties of these iron-sulfur proteins Adx WT and mutant forms of adrenodoxins. Adx WT, mutant forms R106D and D109R have redox potentials E_1/2 significantly more negative than cytochromes P450 (–579 ± 10 mV, –590 ± 15 mV, and –528 ± 10 mV, respectively). These results suggest that Adx WT and mutant forms may be electron donors in the cytochrome P450 systems.