In vitro characterization of FdmV as an amide synthetase that catalyzes FDM C and FDM M-3 amidation to afford FDM B and FDM M-6, respectively. A, chemical synthesis of FDM B from FDM C. B, FdmV-catalyzed amidation of FDM C and FDM M-3 to FDM B and FDM M-6, respectively. C, kinetic analysis of FdmV-catalyzed amidation of FDM C with variable FDM C and saturating l-Gln and ATP. D, FdmV-catalyzed amidation of FDM C utilizing l-Gln, free NH3, or l-Asn as an ammonia source: completed assay with boiled FdmV as a control (I) and identical assays with l-Gln (II), CH3CO2NH4 (III), or l-Asp (IV) as an ammonia source. ○, FDM C; ♢, FDM B.