Carbohydrate sulfotransferase9, 11, 12 and 13 (CHST9, 11, 12 and 13) catalyse the transfer of sulfate from PAPS to position 4 of the N-acetylgalactosamine (GalNAc) residue of chondroitin (Kang et al. 2001, Okuda et al. 2000, Hiraoka et al. 2000, Kang et al. 2002 respectively).