O-antigen group O:21 polymerase yielding a very long O antigen chain length (100 repeat units)
100.0 udcdpgalnac_b1_3_gal_a1_4_gal_b1_3_galnac_a1_3_glcnac_p ⇌ 99.0 udcpdp_p + OA21_VL_p