Serine- O-galactosyl linkages in glycopeptides from carrot cell walls

Abstract

Cell walls obtained from carrot disks aged for 6 days were treated with mild acid to remove the arabinosyl sidechains from the hydroxyproline residues of extensin, and subsequently digested with trypsin. The peptides in the tryptic digest were fractionated according to MW by gel filtration and further purified with Dowex 5OX2. The peptides were rich in hydroxyproline and contained small amounts of carbohydrate, especially galactose. Treatment of the glycopeptides with NaOH in the presence of Na 2SO 3 resulted in a considerable loss of serine residues (up to half in some fractions) and the formation of cysteic acid. Free carbohydrate, consisting mostly of galactose was released by this treatment. Treatment with NaOH in the presence of NaBH 4, resulted in the release of carbohydrate sidechains which primarily contained galactitol and galactose. The data indicate that the serine- O-galactosyl linkage occurs in glycopeptides of different sizes and is most abundant in the hydroxyproline-rich glycopeptide fractions.