Enzymatic conversion of proteins to glycoproteins

The enzymatic transfer of the oligosaccharide moiety from an oligosaccharide-lipid to denatured forms of three secretory proteins--ovalbumin, alpha-lactalbumin, and ribonuclease A--has been demonstrated utilizing a membrane fraction from hen oviduct. Based on a survey of 10 proteins denatured by sulfitolysis, the presence of the tripeptide sequence -Asn-X-Thr-Ser- (X represents a variable amino acid) appears to be necessary but not sufficient for the protein to serve as acceptor in vitro. The results of this investigation also suggest that unfolding of the polypeptide chain is required in order to expose sites for carbohydrate attachment.