L-FUCOSE IS ACCUMULATED VIA A SPECIFIC TRANSPORT-SYSTEM IN EUKARYOTICCELLS

L-Fucose is a monosaccharide normally present at low concentrations in serum and is the only levorotatory sugar utilized by mammalian system s. The metabolism of L-fucose is only partially understood. In this re port, we characterize the uptake of L-fucose by four widely varying ma mmalian cell lines (murine neuroblastoma, bovine aortic endothelial, m urine cerebral microvessel endothelial, and Madin-Darby canine kidney cells). Based on the criteria of saturability and specificity of L-fuc ose uptake, we conclude that L-fucose is accumulated via a specific re cognition mechanism. Accumulation of L-fucose at 4 degrees C and in th e presence of colchicine and cytochalasin D rules out receptor-mediate d endocytosis as an uptake mechanism. Thus, the accumulation appears t o be via a carrier system. Using a variety of criteria, we determined that L-fucose is not taken up by a glucose transporter system. Accumul ation of L-[5,6-H-3]fucose is Na+-independent and reduced by loading c ells with L-fucose or depleting the cell of its phosphorylation capabi lity, suggesting that the uptake of L-fucose is by passive facilitativ e diffusion. A significant amount of the L-fucose taken up by each of the four cell types was incorporated into protein and secreted into th e medium.