Fig. 2. (a) The structures of the active site, precursor, cofactor and residues involved in the enzymatic decarboxylation of α,β-unsaturated acid using Fdc1 enzyme and prFMN^im cofactor obtained from DFT/B3LYP/DZP geometry optimizations.⁷ (b) An example of the model active site cluster (St0) used in the study of the prFMN^im → prFMN^ket photoisomerization. Dash lines show the residue network distances. Int = intramolecular proton transfer in the H-bond of prFMN^im; Ext = intermolecular proton transfer in the H-bond between prFMN^im and Glu282; C^Arg173_R, C^Gln190_R, C^Glu277_R and C^Glu282_R = carbon atoms of the CH₃ groups that substitute the carbon atoms of the Fdc1 backbone.