This compound, 4-Methylumbelliferyl β-D-Galactopyranoside-6-sulfate sodium salt, serves as a fluorogenic substrate in sequential enzymatic assays for detecting arylsulfatase A and β-galactosidase activities. The sulfate group at the 6-position of the galactose is first cleaved by arylsulfatase A to yield 4-Methylumbelliferyl β-D-galactopyranoside, which is then hydrolyzed by β-galactosidase to release the fluorescent product 4-methylumbelliferone (4-MU). This enables sensitive and specific quantification of enzyme activities using fluorescence detection. It is widely used in biochemical and molecular biology research, particularly for studying lysosomal enzyme functions and glycosphingolipid metabolism. In diagnostic applications, it aids in identifying deficiencies in these enzymes, such as in metachromatic leukodystrophy (arylsulfatase A) and GM1 gangliosidosis (β-galactosidase), facilitating bacterial strain differentiation in microbiology and analysis of gene expression in cellular systems.