Cytochrome (cyt) P450s comprise the enzyme superfamily responsible for human oxidative metabolism of a majority of drugs and xenobiotics. Electronic delivery of electrons to cyt P450s could be used to drive the natural catalytic cycle for fundamental investigations, stereo- and regioselective synthesis, and biosensors. We describe herein 30 nm nanometer-thick films on electrodes featuring excess human cyt P450s and cyt P450 reductase (CPR) microsomes that efficiently mimic the natural catalytic pathway for the first time. Redox potentials, electron-transfer rates, CO-binding, and substrate conversion rates confirmed that electrons are delivered from the electrode to CPR, which transfers them to cyt P450. The film system enabled electrochemical probing of the interaction between cyt P450 and CPR for the first time. Agreement of film voltammetry data with theoretical simulations supports a pathway featuring a key equilibrium redox reaction in the natural catalytic pathway between reduced CPR and cyt P450 occurring within a CPR-cyt P450 complex uniquely poised for substrate conversion.