Graphic diagram of the modification of the repeating units in the HS/HP chain. Numbers on steps correspond to the reactions catalyzed by enzymes encoded by the following genes (1): NDST1, NDST2, NDST3, NDST4, (2): GLCE, (3): HST2T1, (4): HS6ST1, HS6ST2, HS6ST3, and (5): HS3ST1, HS3ST2, HS3ST3A1, HS3ST3B1, HS3ST4, HS3ST5, HS3ST6. While the initial, unsulfated substrate is believed to be modified by enzymes 1–5, in that order, the figure includes all other permutations that are possible to achieve the final product, HP/HS.