Catalyzes the adenylation of flavin mononucleotide (FMN) to form flavin adenine dinucleotide (FAD) coenzyme. ATP + FMN + H(+) = diphosphate + FAD kcat is 1.28x10(-1) sec(-1) with FMN as substrate (PubMed:18713732). kcat is 1.28x10(-1) sec(-1) with ATP as substrate (PubMed:18713732). Cofactor biosynthesis; FAD biosynthesis; FAD from FMN: step 1/1. A number of isoforms are produced. According to EST sequences.