4-Methylumbelliferyl ?-L-fucopyranoside has been used:as a substrate in ?-L-fucosidase 1 (?-L-FUCA-1) enzyme assays to convert it to the fluorescent product 4-methylumbelliferone (4MU) for finding the distribution of the membrane-associated ?-L-FUCA-1 of human spermas a fluorogenic substrate in enzyme assays to evaluate the stability of both the seminal plasma and membrane-associated ?-l-fucosidaseas a substrate to measure the enzymatic activity of ?-L-FUCA-1 of cell extracts from TPC-1, BCPAP, 8505C, and CAL62 cell lines