Old yellow enzyme (OYE)-like FMN binding domain. OYE was the first flavin-dependent enzyme identified, however its true physiological role remains elusive to this day. Each monomer of OYE contains FMN as a non-covalently bound cofactor, uses NADPH as a reducing agent with oxygens, quinones, and alpha,beta-unsaturated aldehydes and ketones, and can act as electron acceptors in the catalytic reaction. Members of OYE family include 12-oxophytodienoate reductase, pentaerythritol tetranitrate reductase, morphinone reductase, and related enzymes.