Structure of carbohydrate unit A or porcine thyroglobulin.
The unit A-type glycopeptides were purified from porcine thyroglobulin by Pronase digestion followed by chromatography on a DEAE-Sephadex A-25 column. These glycopeptides were separated into five fractions (UA-I, -II, -IV and -V) by Dowex 50W (X2) column chromatography. Fractions UA-I, -II, -III, -IV and -V were found to have the compositions (Man)9(GlcNAc)2-Asn, (Man)8(GlcNAc)2-Asn, (Man)7(GlcNAc)2-Asn, (Man)6(GlcNAc)2-Asn and (Man)5(GlcNAc)2-Asn respectively. The structures of these five fractions were investigated by the combination of exo- and endo-glycosidase digestions, methylation analysis. Smith periodate degradation and acetolysis. The results showed that fraction UA-V had the simplest structure: see formula in text. The larger glycopeptides (fractions UA-I, -II, -III and -IV) contained additional mannose residues alpha (1 leads to 2)-linked to the terminal mannose residues in the above core structure. These unit A-type glycopeptides appear to be biosynthetic intermediates that are to be processed to form complex-type glycopeptides (unit B-type sugar chains).
D000818:Animals; D002240:Carbohydrate Sequence; D002241:Carbohydrates / Q000032:analysis*; D002850:Chromatography, Gel; D006020:Glycopeptides / Q000032:analysis; D008361:Mannosidases; D008745:Methylation; D009844:Oligosaccharides / Q000032:analysis; D013552:Swine; D013954:Thyroglobulin
D002241:Carbohydrates; D006020:Glycopeptides; D009844:Oligosaccharides; D013954:Thyroglobulin; D008361:Mannosidases