May function as storage protein that sequesters riboflavin and related compounds, thereby protecting the cell against undesirable reactions mediated by the free flavins. Binds and sequesters riboflavin, lumiflavin and lumichrome. Can also bind FAD and FMN (in vitro), but has low affinity for FAD and even lower affinity for FMN. Protects bound flavins against light damage; Trp-36 rapidly quenches the flavin excited state. Promotes the conversion of bound riboflavin to lumichrome.