Which substances are demonstrated by Alcian Blue at pH 1.0 and pH 2.5?

• A. Sulfated acid mucopolysaccharides
• B. Carboxylated mucopolysaccharides
• C. Glycogen
• D. Amyloid

Answer: (A)

Alcian Blue binds to negatively charged mucosubstances, specifically acidic mucopolysaccharides (glycosaminoglycans). The pH controls which groups are ionized and can bind the dye. At pH 1.0, only sulfated mucopolysaccharides carry enough negative charge to bind Alcian Blue, while carboxylated mucopolysaccharides are not ionized and do not stain. At pH 2.5, both sulfated and carboxylated mucopolysaccharides can be ionized, but the substances that are demonstrable at both pH levels are the sulfated acid mucopolysaccharides. Therefore, the staining demonstrated at pH 1.0 and pH 2.5 corresponds to sulfated acid mucopolysaccharides (such as sulfated glycosaminoglycans). Glycogen and amyloid are not acidic mucopolysaccharides and do not show this staining pattern with Alcian Blue.