Scheme 9. Proposed mechanism for a fungal RedAm-catalyzed reductive amination using residue numbering from AtRedAm.⁶⁰ (A) The active site of AtRedAm binds NADPH, (B) cyclohexanone, and (C) the amine sequentially, to form a quaternary complex; (D) the amine is activated by D175 for attack at the electrophilic carbon of the ketone to give a hemiaminal intermediate; (E) the hemiaminal intermediate loses water to give the iminium intermediate; (F) this is reduced by NADPH to give the amine product and NADP⁺; (G) the amine product and (H) NADP⁺ are sequentially expelled from the active site to regenerate the enzyme for another catalytic cycle.