Plasma membrane transporter mediating the uptake by cells of the water soluble vitamin B2/riboflavin that plays a key role in biochemical oxidation-reduction reactions of the carbohydrate, lipid, and amino acid metabolism (PubMed:20463145, PubMed:22273710, PubMed:24264046, PubMed:27702554). Humans are unable to synthesize vitamin B2/riboflavin and must obtain it via intestinal absorption (PubMed:20463145). riboflavin(in) = riboflavin(out) Activity is strongly inhibited by riboflavin analogs, such as lumiflavin, flavin mononucleotide (FMN), flavin adenine dinucleotide (FAD), by methylene blue, and to a lesser extent by amiloride. Riboflavin transport is Na(+)-independent at low pH but significantly reduced by Na(+) depletion under neutral pH conditions. Predominantly expressed in testis. Highly expressed in small intestine and prostate. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Belongs to the riboflavin transporter family. It is uncertain whether Met-1 or Met-5 is the initiator.