The pattern of glycosylation of newly synthesized human and routine immunoglobulin μ-chains varies according to the degree of inhibition of N-glycosylation effected by using the antibiotic tunicamycin. Tunicamycin, at high concentrations, can apparently block N-glycosylation of μ-chains completely as judged by SDS-PAGE analysis of the biosynthetically labelled products. At lower concentrations of tunicamycin, fully giycosy]ated and totally non-glycosylated chains were the predominant molecular species. The paucity of the predicted partially glycosylated μ-chains leads us to suggest that the addition of oligosaccharides to the appropriate acceptor sites is a cooperative process.
Long exposure of fluorographs reveals each of the predicted intermediately glycosylated forms of the μ-chain, and counting the number of bands on such fluorographs may prove useful in the preliminary determination of the number of N-linked oligosaccharides in a given glycoprotein.