Single-turnover experiments using wild-type riboflavin synthase and 6,7-dimethyl-8-ribityllumazine, respectively, with Compound Q as substrate. 6,7-Dimethyl-8-ribityllumazine as substrate (○) afforded riboflavin (▵). Compound Q as substrate (♦) afforded 6,7-dimethyl-8-ribityllumazine (●) and riboflavin (▴).