FunctionRegulatory subunit of lactose synthase, changes the substrate specificity of galactosyltransferase in the mammary gland making glucose a good acceptor substrate for this enzyme. This enables LS to synthesize lactose, the major carbohydrate component of milk. In other tissues, galactosyltransferase transfers galactose onto the N-acetylglucosamine of the oligosaccharide chains in glycoproteins.
Tissue specificityMammary gland specific. Secreted in milk.
Sequence similaritiesBelongs to the glycosyl hydrolase 22 family.