Acetylgalactosamine (also known as N-acetyl-D-galactosamine or GalNAc) is a type of sugar molecule called a hexosamine that is commonly found in glycoproteins and proteoglycans, which are complex carbohydrates that are attached to proteins and lipids. It plays an important role in various biological processes, including cell-cell recognition, signal transduction, and protein folding.

In the context of medical research and biochemistry, Acetylgalactosamine is often used as a building block for synthesizing glycoconjugates, which are molecules that consist of a carbohydrate attached to a protein or lipid. These molecules play important roles in many biological processes, including cell-cell recognition, signaling, and immune response.

Acetylgalactosamine is also used as a target for enzymes called glycosyltransferases, which add sugar molecules to proteins and lipids. In particular, Acetylgalactosamine is the acceptor substrate for a class of glycosyltransferases known as galactosyltransferases, which add galactose molecules to Acetylgalactosamine-containing structures.

Defects in the metabolism of Acetylgalactosamine have been linked to various genetic disorders, including Schindler disease and Kanzaki disease, which are characterized by neurological symptoms and abnormal accumulation of glycoproteins in various tissues.