Folate receptors bind folate and reduced folic acid derivatives and mediates delivery of tetrahydrofolate to the interior of cells. It is then converted from monoglutamate to polyglutamate forms - such as 5- methyltetrahydrofolate - as only monoglutamate forms can be transported across cell membranes. Polyglutamate forms are biologically active enzymatic cofactors required for many folate-dependent processes such as folate-dependent one-carbon metabolism. These proteins are attached to the membrane by a GPI anchor. A riboflavin-binding protein required for the transport of riboflavin to the developing oocyte in chicken also belong to this family.