Significance Cytochrome P450 activates molecular oxygen to hydroxylate various molecules. This process requires the transfer of electrons from a redox partner, which further requires formation of a specific protein–protein complex. A question of increasing importance is whether or not the interaction between the P450 and its redox partner results in functionally important structural changes required for activity. The present work addresses the question of whether the redox partner favors binding to a specific conformer. This question is critically important in understanding how P450s activate molecular oxygen.