Riboflavin Biosynthesis: Mapping the Tagged Lines of a Complex Metabolic Design

Nearly 150 years ago, riboflavin was first isolated as the water-soluble, yellow-green, fluorescent "lactochrome," a discovery that added the earliest bright stroke to what would become a complex metabolic mural. The ribityl-isoalloxazine structure was fully defined nearly a century ago, and from the 1970s through the 1990s, a series of elegant biochemical studies began tracing the lines of biosynthesis with increasing definition, including isotopic labeling experiments (¹³C, ¹⁵N) that effectively tagged substrate atoms to follow their movement through the pathway. In more recent years, presteady state analyses and high-resolution crystal structures have brought sharper focus to the proposed enzymatic mechanisms, adding depth and shading to the emerging picture. The purpose of this article is to define the current state of our understanding of the enzymatic mechanisms that compose the riboflavin biosynthetic pathway, bringing the latest evidence together as an updated rendering of this intricate biochemical (master)piece.