The enzymic degradation of ovalbumin and its glycopeptides

1. Ovalbumin glycopeptides, freed from all amino acids other than aspartic acid and a small proportion of leucine by repeated digestion with Pronase, were hydrolysed by 1-aspartamido-β-N-acetylglucosamine amidohydrolase (glycoaspartamidase) to the corresponding oligosaccharides. The glycoaspartamidase did not attack ovalbumin itself. 2. Ovalbumin, with mannose/hexosamine ratio 5:4, lost 1·5moles of N-acetylglucosamine and more than 2moles of mannose after incubation with α-mannosidase and β-N-acetylglucosaminidase respectively. 3. In ovalbumin glycopeptides with approximate mannose/hexosamine ratios 5:3 and 5:4, one and two N-acetylglucosamine residues respectively were accessible to the action of β-N-acetylglucosaminidase. 4. A mixture of α-mannosidase and β-N-acetylglucosaminidase, acting on an ovalbumin glycopeptide with mannose/hexosamine ratio 5:3·7, removed nearly 4moles of mannose and 1·5moles of N-acetylglucosamine. 5. α-Mannosidase removed about 1·5moles of mannose from the ovalbumin oligosaccharide with mannose/hexosamine ratio approx. 5:3. The subsequent action of β-N-acetylglucosaminidase liberated less than 1mole of N-acetylglucosamine and made at least 1mole further of mannose accessible to α-mannosidase action. 6. It is concluded that the carbohydrate moiety of ovalbumin is linked through a glycosyl group to asparagine. In a molecule with mannose/hexosamine ratio 5:4, there are two β-N-acetylglucosamine residues linked together in a terminal position, followed by α-mannose. There is also present a side chain containing two α-mannose units.