Abstract
The mechanism of periodic acid (PA) -Schiff staining was investigated by analysis of materials isolated from connective tissue derivatives and secretory products which in sections stain to a variable extent with the PA-Schiff technique. The methods devised for the isolation of these two classes of materials involved extraction with alkali and saline respectively, followed by precipitation with ethanol.
Chemical determinations reveal the presence of hexose, hexosamine, methylpentose, nitrogen, and perhaps sialic acid in these materials (Table 3). The hexose content parallels the intensity of PA-Schiff staining (Tables 1 and 2). The monosaccharide components detected by paper chromatography are galactose and fucose, mannose in most cases and occasionally glucose and rhamnose, but not uronic acid . The individual monosaccharide components of each material differ in a quantitative as well as qualitative manner which could be reduplicated on repeated extractions, a fact considered to be presumptive evidence of the homogeneity of the isolated substances.
After treatment of the materials with periodic acid, all glucose and fucose residues and most galactose and mannose residues are eliminated; and, therefore, these monosaccharides must be present in such a form that their 1,2-glycol groups are free for oxidation with periodic acid.
Since all PA-Schiff reactive materials under investigation contain bound galactose and fucose, as well as hexosamine and probably sialic acid, and are associated with protein, they make up a distinct class of substances, referred to as carbohydrate-protein complexes. It is proposed that, once glycogen has been removed from sections with amylase, the PA-Schiff technique is specific for the carbohydrate-protein complexes thus defined.