Since β3GalT5 is a membrane-boundglycoprotein and exists as two isozymes, we first designed specificprobes and dicer-substrate siRNA to knockdown specific isozymes inbreast cancer cells and found that the expression level and activityof β3GalT5–1 were higher than those of β3GalT5–2.We also investigated the impact of glycosylation on protein foldingand activity and found that the soluble domain of β3GalT5–1(residues N29–V310) expressed in insect cells is an efficientcatalyst for synthesis. This evidence concerns the gene B3GALT5 and cancer.