Catalyzes the phosphorylation of riboflavin (vitamin B2) to form flavin mononucleotide (FMN) coenzyme. ATP + riboflavin = ADP + FMN + H(+) Zinc or magnesium. Cofactor biosynthesis; FMN biosynthesis; FMN from riboflavin (ATP route): step 1/1. 90% microsomal. 10% mitochondrial. Found to be present in the inner membrane of mitochondria. The C-terminus is located in the matrix. FMN1 is essential for growth on rich medium. Present with 830 molecules/cell in log phase SD medium. Belongs to the flavokinase family. The subcellular location of this enzyme needs further confirmation.