Involved in the interconversion between alpha- and beta-L-fucoses. L-Fucose (6-deoxy-L-galactose) exists as alpha-L-fucose (29.5%) and beta-L-fucose (70.5%), 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. alpha-L-fucose = beta-L-fucose Carbohydrate metabolism; L-fucose metabolism. Mainly homodimer, but exists also as homotetramer, homooctamer, and homodecamer. The homodimeric form seems catalytically inactive (By similarity). Belongs to the RbsD / FucU family.