FUOM, also known as fucose mutarotase and FucM, belongs to the RbsD / FucU family. FUOM is involved in the interconversion between alpha- and beta-L-fucoses. L-Fucose has two isforms: alpha-L-fucose (29.5%) and beta-L-fucose (7.5%). The beta-form is metabolized through the salvage pathway. GDP-L-fucose formed either by the de novo or salvage pathways is transported into the endoplasmic reticulum, where it serves as a substrate for N- and O-glycosylations by fucosyltransferases. Fucosylated structures expressed on cell surfaces or secreted in biological fluids are believed to play a critical role in cell-cell adhesion and recognition processes. FUOM mainly exists as homodimer, but also functions as homotetramer, homooctamer, and homodecamer. FUOM's homodimeric form seems catalytically inactive.