Catalyzes the addition of sialic acid in alpha 2,8-linkage to the sialic acid moiety of the ganglioside GM3 to form ganglioside GD3; gangliosides are a subfamily of complex glycosphingolipds that contain one or more residues of sialic acid (   ). Can catalyze the addition of a second alpha-2,8-sialic acid to GD3 to form GT3 . Can use GM1b, GD1a and GT1b as acceptor substrates to synthesize GD1c, GT1a and GQ1b respectively . Can synthesize unusual tetra- and pentasialylated lactosylceramide derivatives identified as GQ3 (II3Neu5Ac4-Gg2Cer) and GP3 (II3Neu5Ac5-Gg2Cer) in breast cancer cells .
Subcellular locations: Golgi apparatus membrane
Strongly expressed in melanoma cell lines, adult and fetal brain and to a lesser extent in adult and fetal lung.