Ultrastructural distribution of lectin-binding sites on gastric superficial mucus-secreting epithelial cells The role of Golgi apparatus in the initial glycosylation

Normal human gastric epithelial cells were ex-amined by electron microscopy using each of five bi-otinylated lectins [Ulex europaeus agglutinin I (UEA-I), peanut agglutinin (PNA), wheat germ agglutinin (WGA), soybean agglutinin (SBA) and Dolichos biflorus agglutin-in (DBA)] as a probe. We employed 35 gastric surgical specimens removed from complicated peptic disease. The lectin-binding sites were revealed with streptavidin-col-loidal gold complex. All specimens were embedded in Spurr and LR White resins. In superficial foveolar epithe-lial cells, the lectins used were generally positive in all cell types (mainly UEA-1 and PNA) on the Golgi region and mucus cytoplasmic vacuoles, with many variations among cells in the same case. On the other hand, extracel-lular mucus was negative for WGA. Labelling with PNA revealed a biphasic pattern (peripheral positivity) on mu-cous droplets in surface and fove01ar cells. The cis side of the Golgi apparatus was labelled with SBA and PNA and rough endoplasmic reticulum with SBA (only five cases). Lectin-binding variability could be related to het-erogeneous composition of gastric mucus. Our results with SBA suggest initiation of O-glycosylation at the Golgi apparatus; however a role of the rough endoplas-mic reticulum cannot be excluded (N-glycosylation). We propose the following sequence of sugar addition to the carbohydrate side-chains of gastric glycoproteins: (1) GaNAc (Golgi apparatus cis-side), (2) GlcNAc (Golgi ap-paratus intermediate face), (3) GalNac or Gal, C~-L-fucose (Golgi apparatus trans-side).