The pMCSG7-acmb plasmid was used as a template for site-directed mutagenesis introducing point mutations (Y115F, Y118F, Y363F, Y467F, Y536F, G540P) into the AcmB gene. The details of the procedure are available in SI. The FAD content in the expressed enzymes was estimated as the ratio of the spectrophotometrically measured AcmB-FAD concentration (εAcmB 450 nm = 12 094 M -1 cm -1 , determined as in ) to the total protein concentration determined according to the Bradford method .