The structure of a glycopeptide purified from porcine thyroglobulin

1. The structure of a purified glycopeptide isolated from porcine thyroglobulin was studied by sequential hydrolysis with specific glycosidases, by periodate oxidation and by treatment with galactose oxidase. 2. Sequential hydrolysis with several combinations of neuraminidase, α-l-fucosidase, β-d-galactosidase, β-N-acetyl-d-glucosaminidase and α-d-mannosidase presented the evidence for the following structure. 3. The monosaccharide sequence of the peripheral moiety of the heteropolysaccharide chain was sialic acid→galactose→N-acetylglucosamine. Some of the galactose residues were non-reducing end-groups with the sequence galactose→N-acetylglucosamine. 4. After removal of the peripheral moiety composed of sialic acid, fucose, galactose and N-acetylglucosamine, α-mannosidase released 1.4mol of mannose/mol of glycopeptide, indicating that two of the three mannose residues were located between peripheral N-acetylglucosamine and internal N-acetylglucosamine or mannose. 5. Periodate oxidation and sodium borohydride reduction confirmed the results obtained by enzymic degradation and gave information concerning the position of substitution. 6. Based on the results obtained by enzymic hydrolysis and periodate oxidation together with the treatment with galactose oxidase, a structure is proposed for the glycopeptide.