Abstract
In order to study structure-function relationships of lysosomal enzymes, human liver β- N-acetylhexosaminidase (2-acetamido-2-deoxy-β- d-hexoside acetamidodeoxyhexohydrolase, EC 3.2.1.52) has been purified by an extraction/affinity chromatography/ion-exchange procedure. The isoenzymes A and B, native as well as neuraminidase-treated, were incubated with a partially purified preparation of bovine colostrum sialyltransferase (CMP- N-acetylneuraminate : d-galactosyl-glycoprotein N-acetylneuraminyltransferase, EC 2.4.99.1). Native β- N-acetylhexosaminidases were found to be poor acceptors for the sialyltransferase used. However, incorporation of sialic acid into neuraminidase-treated β- N-acetylhexosaminidase A and B amounted to a 58 and 72% saturation of the theoretical acceptor sites, respectively. The acceptor specificity of the sialyltransferase suggests that Galβ(1 → 4)-GlcNAc units may be present on at least part of the β- N-acetylhexosaminidase A and B molecules. However, oligomannosidic-type chains may also occur on the lysosomal enzyme, as shown by sugar composition of the enzyme. The presence and/or amount of sialic acid residues does not appear to affect the kinetic properties of β- N-acetylhexosaminidase A and B towards 4-methylumbelliferyl glycoside substrate.
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