If not stated otherwise all chemicals were purchased from Sigma Aldrich (Buchs, Switzerland). NADH was purchased from GERBU (Heidelberg, Germany), D-fructose, D-sorbose and L-fructose were purchased from Carbosynth (Berkshire, UK), D-tagatose and L-sorbose were obtained from Sigma Aldrich (Buchs, Switzerland). D-psicose was produced inhouse by epimerization of D-fructose to D-psicose with D-tagatose epimerase and separation of D-psicose from D-fructose by continuous chromatography [26] . Restriction enzymes and polymerases were obtained from New England Biolabs (Ipswich, MA, USA) and oligonucleotides from Microsynth (Balgach, Switzerland).
Molecular Biology: General molecular biology was performed according to standard protocols [27] . All PCRs were generated using Phusion High-Fidelity Polymerase (NEB). Primers used for cloning are listed in Table S1 and all plasmids used and generated in this work are listed in Table S2. All general cloning work was done in E. coli Top10 cells (Invitrogen).
Molecular Biology: General molecular biology was performed according to standard protocols [27] . All PCRs were generated using Phusion High-Fidelity Polymerase (NEB). Primers used for cloning are listed in Table S1 and all plasmids used and generated in this work are listed in Table S2. All general cloning work was done in E. coli Top10 cells (Invitrogen).