4-Methylumbelliferyl 2-sulfamino-2-deoxy-α-D-Glucopyranoside (4-MU-α-GlcNS) is a fluorogenic substrate of heparin sulphamidase. Heparin sulphamidase cleaves 4-MU-α-GlcNS to yield 4-MU-α-GlcNH2, which is then cleaved by α-glucosaminidase to release the fluorescent product 4-MU, which displays an emission maxima of 445-454 nm. The excitation maxima for 4-MU is pH-dependent: 330, 370, and 385 nm at pH 4.6, 7.4, and 10.4, respectively. 4-MU-α-GlcNS has been used to quantify heparin sulphamidase deficiencies associated with Mucopolisaccaridosis IIIA and other lysosomal disorders.
4-Methylumbelliferyl β-D-Galactopyranoside-6-sulfate (sodium salt) (4-MU-Gal-6S) is a fluorogenic substrate used to quantify N-acetylgalactosamine-6-sulphatase (GALNS) activity. 4-MU-Gal-6S is cleaved by GALNS to release the fluorescent moiety 4-MU. 4-MU fluorescence is pH-dependent with excitation maxima of 320 and 360 nm at low (1.97-6.72) and high (7.12-10.3) pH, respectively, and an emission maximum ranging from 445 to 455 nM, increasing as pH decreases. It has been used to detect Morquio disease type A, a lysosomal storage disorder in which GALNS is deficient. 4-MU-Gal-6S can be used to assess GALNS activity in a very small blood volume to determine the extent of deficiency.