N-Acetyl-β-d-hexosaminidases (EC
3.2.1.52) are exo-acting glycosyl hydrolases that remove N-acetyl-β-d-glucosamine (Glc-NAc) or N-acetyl-β-d-galactosamine (Gal-NAc) from the nonreducing
ends of various biomolecules including oligosaccharides, glycoproteins,
and glycolipids. The same enzymes are sometimes called N-acetyl-β-d-glucosaminidases, and this review article
employs the shorthand descriptor HEX(NAG) to indicate that the terms
HEX or NAG are used interchangeably in the literature. The wide distribution
of HEX(NAG) throughout the biosphere and its intracellular location
in lysosomes combine to make it an important enzyme in food science,
agriculture, cell biology, medical diagnostics, and chemotherapy.
For more than 50 years, researchers have employed chromogenic derivatives
of N-acetyl-β-d-glucosaminide in basic
assays for biomedical research and clinical chemistry. Recent conceptual
and synthetic innovations in molecular fluorescence sensors, along
with concurrent technical improvements in instrumentation, have produced
a growing number of new fluorescent imaging and diagnostics methods.
A systematic summary of the recent advances in optical sensors for
HEX(NAG) is provided under the following headings: assessing kidney
health, detection and treatment of infectious disease, fluorescence
imaging of cancer, treatment of lysosomal disorders, and reactive
probes for chemical biology. The article concludes with some comments
on likely future directions.