... types of covalent flavin–protein linkages. FMN is show in black, FAD in black and gray, and known linking amino acids in green. Sites of covalent attachment are indicated by arrows. The numbering of ... flavoproteins, theflavin is covalently linked to an amino acid that ispart of the FAD-binding domain, whereas in VAO,the corresponding histidine is part of the substrate-binding domain. In addition, ... [70]. In all of the cases described above, mainly histidyl–FAD-containing enzymes, it appears that the func-tional benefit of acquiring and retaining a covalentflavin–protein link is to increase...