Figure 1. MurB-catalyzed FAD- and NADPH-dependent reduction of UNAGEP to UNAM.

In the first half reaction (upper panel) the 4-pro-S hydrogen and two electrons from the reduced nicotinamide C4 atom are transferred to the N5 atom of the isoalloxazine resulting in NADP⁺ and reduced FAD. In the second half reaction (lower panel) the hydride is transferred to the C3 atom of the UNAGEP enolpyruvyl group, reducing the enolpyruvyl to a lactoyl group and thus converting UNAGEP to UNAM.