N-acetylgalactosamine is a constituent of glycosaminoglycans and O-linked glycoproteins.

Glycosaminoglycans - Glycosaminoglycans are heteropolysaccharides containing either N-acetylgalactosamine or N-acetylglucosamine as one of their monomeric units. Examples include chondroitin sulfates and keratan sulfates of connective tissue, dermatan sulfates of skin, and hyaluronic acid. All of these are acidic, through the presence of either sulfate or carboxylate groups (Figure 9.23).

O-Linked Glycoproteins - The most common O-linkage in glycoproteins involves a terminal N-acetylgalactosamine residue in the oligosaccharide linked to a serine or threonine residue of the protein (Figure 9.28).

N-acetylgalactosamine is a component of the ABO blood group antigens (Figure 9.29). The presence of N-acetylgalactosamine on the end of the oligosaccharide gives a person type A blood.