Activity of partially purified UDP-N-acetyl-alpha-D-galactosamine: polypeptide N-acetylgalactosaminyltransferase with different peptide acceptors

As part of investigations on the role of the UDP-GalNAc-ribosome complex in the initial O-glycosylation of proteins, we have isolated from porcine gas tric mucosa GalNAc-transferase, mucin and apomucin, and its three fractions containing carbohydrate in the amounts: I - 1.6%, II - 0.65% and III - 0.0 0% (wt/wt) of apomucin mass. Amino acid analysis showed that fractions I and II contained slightly highe r amounts of serine and threonine as compared to native mucin and apomucin. The short peptide Pro-Thr-Ser-Ser-Pro-Ile-Ser-Thr was the most effectively glycosylated. Our apomucin preparations are also good accepters of GalNAc a nd can be used for testing of O-glycosylation in vitro.