Catalyzes the transfer of N-acetylneuraminyl groups onto glycan chains in glycoproteins (, ). Shows a preference for N-acetylgalactosamine (GalNAc) residues already modified by the addition of galactose or galactose followed by sialic acid in alpha-2,3 linkage .
Subcellular locations: Golgi apparatus membrane
Expressed in skeletal muscle, heart, kidney, placenta, lung and leukocytes.