The first step in mucin-type O-glycosylation is catalyzed by UDP N-acetylgalactosamine (GalNAc):polypeptide GalNAc transferases (EC 188.8.131.52). Each member of this large enzyme family has a unique substrate specificity and expression profile. GALNT9 belongs to a subfamily of GALNTs found only in vertebrates. Other members of this subfamily include GALNT8 (606250), GALNT19 (615137), and GALNT18 (615136). Due to critical substitutions in a conserved catalytic motif, members of this subfamily lack significant GalNAc transferase activity (Li et al., 2012). ###Copied from OMIM###
This page does not indicate all of the enzymatic reaction, and expression of "GALNT9".