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:18632736, PubMed:20463145). Humans are unable to synthesize vitamin B2/riboflavin and must obtain it via intestinal absorption (PubMed:20463145). (Microbial infection) May function as a cell receptor to retroviral envelopes similar to the porcine endogenous retrovirus (PERV-A). riboflavin(in) = riboflavin(out) The activity is strongly inhibited by riboflavin analogs, such as lumiflavin (PubMed:18632736, PubMed:20463145). Weakly inhibited by flavin adenine dinucleotide (FAD) (PubMed:18632736, PubMed:20463145). Widely expressed. Highly expressed in the testis, placenta and small intestine. Expressed at lower level in other tissues. The disease is caused by variants affecting the gene represented in this entry. May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay. Belongs to the riboflavin transporter family.