Our proposed cooperative photometallobiocatalytic asymmetric C-N/C-S bond formation involves two discrete catalytic cycles. For clarity, photometallobiocatalytic enantioconvergent azidation of redox-active esters is illustrated as an example (Scheme 1) for this class of enantioselective radical rebound processes. In the photoredox cycle, we envisioned that a judiciously selected photosensitizer such as fluorescein (FL) would oxidize the Fe(II) species in its excited state (FL*/ FL •-= +0.77 V versus SCE in MeOH) 14d, 24 to afford the radical anion state FL •-. This radical anion (FL •-) and related photosensitizer radical anions in their ground state is a potent single electron reductant and is known to promote reductive radical generation with N-hydroxyphthalimide esters. In this single electron transfer process, the radical anion FL •-would also be converted back to the neutral photosensitizer FL, thereby completing the photoredox cycle. Concurrently, in the nonheme biocatalytic cycle, we postulated that the enzymatic iron center would stay in an azide-bound form due to the strong binding affinity of N3 -towards Fe. This enzymatic Fe(II)-N3 species would be rapidly oxidized by the excited state photosensitizer FL*, giving rise to the key Fe(III)-N3 intermediate. PyMol illustration of metapyrocatechase (MPC), a nonheme Fe extradiol dioxygenase, is made from PDB ID: 1MPY. FL: fluorescein, a photocatalyst.