Age-related changes induced by tunicamycin in wheat germ agglutinin binding to chick embryo fibroblasts

The specific roles of N-acetylglucosaminyl and sialyl residues were investigated in the binding of wheat germ agglutinin (WGA) to fibroblasts from 8- and 16-day chick embryos. Cells from the 8-day embryos exhibited two classes of WGA binding site, whereas fibroblasts from 16-day embryos only displayed one. Neuraminidase treatment of fibroblasts from 8-day embryos raised the number of WGA binding sites with a high affinity constant and reduced the number of sites with a low affinity constant. In 16-day cells, neuraminidase treatment reduced the number of WGA binding sites. The data presented here suggest that WGA binds to cell-surface glycoproteins containing sialic acid residues. This tendency was more marked in 16-day than in 8-day cells and corresponded to the finding that neuraminidase released more sialic acid from the surface of 16-day cells than of 8-day cells. Glycosylation of cell-surface N-linked glycoproteins did not seem essential in determining the WGA binding capacity, as shown by the effect of tunicamycin on fibroblasts from both 8- and 16-day embryos. In the absence of N-glycosylated binding sites, WGA bound to O-glycosylated structures and the older tunicamycin-treated embryo cells exhibited a larger number of WGA binding sites than the younger tunicamycin-treated cells, in relation to the increase of the amount of O-glycosylated structures during embryo development.