4-Methylumbelliferyl-α-D-glucopyranoside serves as a fluorogenic substrate for α-glucosidase, used in enzymatic assays. This compound undergoes cleavage by α-glucosidase, releasing 4-methylumbelliferyl (4-MU), a compound whose fluorescence intensity varies with pH. Specifically, 4-MU exhibits excitation peaks at 320 nm and 360 nm in acidic (pH 1.97-6.72) and alkaline environments (pH 7.12-10.3), respectively, and its emission peak ranges between 445 nm and 455 nm, with brightness increasing as the pH drops. Utilizing these properties, 4-Methylumbelliferyl-α-D-glucopyranoside has been effectively applied in the measurement of α-glucosidase activity within infant blood spot samples, acting as a diagnostic marker for Fabry and Pompe diseases. These illnesses are types of lysosomal storage disorders caused by α-glucosidase enzyme deficiency.