Figure 1.

Natural (Upper) and direct-electrode-driven (Lower) catalytic cycles for substrate (camphor) hydroxylation by the P450cam monooxygenase system. Substrate binds with the oxidized form of cytochrome hemoprotein CYP101 (P450cam) to form the protein complex CYP^os, which receives the first electron e₁ from reduced putidaredoxin Pdx^r. Dissolved oxygen is bound in the natural cycle to form the complex CYP_O2^rs, which receives a second electron e₂ from Pdx^r, whereupon the complex decomposes to give the stereospecifically hydroxylated product (5-exo-hydroxy-camphor). In the electrode-driven process, a semiconductor working electrode supplies reducing power to oxidized putidaredoxin Pdx^o, replacing NADH and putidaredoxin reductase PdR as reducing components. Also, oxygen is generated electrochemically at a controlled surface area counter electrode in an anaerobic bioreactor.