A Pathway of Polygalactosamine Formation in Aspergillus parasiticus: Enzymatic Deacetylation of N-Acetylated Polygalactosamine

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Abstract
1 An enzyme which hydrolyzes the acetamido groups of N‐acetylgalactosamine residues in N‐acetylated polygalactosamine was found in the supernatant fraction of Aspergillus parasiticus AHU 7165, a polygalactosamine‐producing strain. 2 N‐Acetylated polygalactosamine was used as a substrate in the purification and characterization of this enzyme. A 140‐fold purification was obtained by means of ammonium sulfate fractionation followed by chromatography on carboxymethylcellulose and DEAE‐cellulose. 3 The enzyme releases about 60–70% of the acetyl groups of N‐acetylated polygalactosamine, giving a product with free amino groups. Whereas the enzyme also deacetylates oligosaccharides with 14 or more N‐acetylgalactosamine units at a rate similar to that of deacetylation of the polymer, it deacetylates shorter oligosaccharides (trimer to hexamer of N‐acetylgalactosamine) much more slowly and is virtually inactive toward disaccharide. Deacetylation can not be detected with bacterial cell wall peptidoglycan, N‐acetylated heparin, partially O‐hydroxyethylated chitin or monomeric N‐acetylgalactosamine derivatives as substrates. 4 This enzyme shows double pH optima of 5.3 and 9.3. The Km value for N‐acetylated polygalactosamine is 0.15 g/l (or 0.54 mM with respect to monosaccharide residues). 5 The occurrence of this enzyme may account for the formation of polygalactosamine with free amino groups.

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