Demonstration of the enzymatic mechanisms of α-N-acetyl-d-glucosamine-1-phosphodiester N-acetylglucosaminidase (formerly called α-N-acetylglucosaminylphosphodiesterase) and lysosomal α-N-acetylglucosaminidase

An enzyme that is capable of removing the outer N-acetylglucosamine residues from phosphodiesters present on the high-mannose-type oligosaccharides of newly synthesized lysosomal enzymes has been described. This enzyme has been called an α-Nacetylglucosaminylphosphodiesterase, based upon its substrate specificity and on inhibitor studies. In this study it is demonstrated by the ¹⁸O enrichment method that the enzyme cleaves the CO bond rather than the OP bond, and therefore acts by a glycosidase type of mechanism. In addition, the enzyme has no significant activity toward α-N-acetylglucosamine 1-phosphate, and therefore requires an underlying phosphodiester for activity. In accordance with the IUB recommendations for enzyme nomenclature, it is therefore suggested that the enzyme be renamed α-N-acetyl-dglucosamine-1-phosphodiester N-acetylglucosaminidase (systematic name, 2-acetamido-2-deoxy-α-d-glucose 1-phosphodiester acetamidodeoxyglucohydrolase). For convenience, the trivial name phosphodiester glycosidase is proposed. Lysosomal α-Nacetylglucosaminidase also has a glycosidase type of mechanism but it is active toward α-N-acetylglucosamine 1-phosphate as well as phosphodiesters with outer N-acetylglucosamine residues.