![Comparison between the flavin bond and Schiff base formation. (A) Shown is the proposed general mechanism for the formation of the covalent flavin–protein bond at the isoalloxazine ring (adapted from Heuts et al. [2009]). Here, B1, B2, and B3 are basic side chains, while L− is the nucleophilic side chains. (B) Schiff base is formed through imine condensation between the carbonyl group of a ligand (here, 5-OP-RU) and the amino group of MR1-Lys43.](https://cdn.rupress.org/rup/content_public/journal/jem/223/2/10.1084_jem.20250711/1/jem_20250711_figs5.png?Expires=1767655164&Signature=11VMD6TV2PJTmNtB2Hj4eA8ibfDOR5NwdhC~b-kEqHzl3jabAMhryxGyAmLJ2XZK7a6PNdjVPS0MgMfsrWV9b~BfmLLxh0uj1AE70IfE02qI5FiJ6zoTXOyADoOGwRcYKyKRgjOgtddjwz63wnoECA36W1GIET8H~YB51kXaORN6Jb-6XBQOQqpqv0Z8RbWeAPDQAqi~xCKxbfW0lFHhVaSfZPCOW97ZJ6KJRbRM4iFZjHJYiEhPKeqEFnzwvD7eVDyqb9X8bLSSjrXYmKMttalMqLThDfN7SIZ6E4o6aXYMbsoXWyOlMJ7rW1Svuj-puJoZ02lB7wQ7H0wdPnMYHg__&Key-Pair-Id=APKAIE5G5CRDK6RD3PGA)
Figure S5.
Comparison between the flavin bond and Schiff base formation. (A) Shown is the proposed general mechanism for the formation of the covalent flavin–protein bond at the isoalloxazine ring (adapted from Heuts et al. [2009]). Here, B1, B2, and B3 are basic side chains, while L− is the nucleophilic side chains. (B) Schiff base is formed through imine condensation between the carbonyl group of a ligand (here, 5-OP-RU) and the amino group of MR1-Lys43.