Periodic acid-Schiff-alcian blue: a method for the differential staining of glycoproteins.

The staining mechanism underlying the periodic acid-Schiff (PAS)-Alcian Blue (AB) sequence has been investigated using a variety of glycoprotein-containing tissues from different organs of the monkey, rat and mouse. The results obtained suggest that reactive carbohydrates contain at least three types of chemical end-groups found in neutral and acidic glycoproteins: (1) PA-engendered aldehyde groups coloured magenta by the Schiff reagent; (2) PA-engendered aldehyde groups coloured blue bisulphite-AB; and (3) naturally occurring acidic (carboxyl and/or sulphate) groups coloured blue by AB only. The PAS-AB sequence showed heterogeneity of glycoprotein structures in the conjunctiva and the duodenal goblet cells. Thus, the PAS-AB sequence is not the simple reverse sequence of AB-PAS but has its own definite and unique staining selectivity and can hence be used as a reliable method for the histochemistry of glycoproteins at the light microscope level.