Catalyzes the conversion of dihydroorotate to orotate (PubMed:2996629). Participates in the pyrimidine biosynthetic pathway (PubMed:2996629). (S)-dihydroorotate + A = AH2 + orotate Binds 1 FMN per subunit. Pyrimidine metabolism; UMP biosynthesis via de novo pathway. Belongs to the dihydroorotate dehydrogenase family.