A. The activity of purified seHAS was determined using the normal activity assay, except the UDP-GlcUA and UDP-GlcNAc concentrations were, respectively, 0.02 mM and 0.035 mM and the indicated nucleotide, nucleotide-sugar or sugar was present at 2 mM. Values are presented as the mean ± SD for duplicate assays in three independent experiments (n=6), which were normalized to the no-addition control (set at 100 %). B. The two substrate concentrations were below their Km values, as in A and the nucleotide and sugar nucleotide concentrations ranged from 0–1 mM: UMP (▪), UDP (•), UTP (▴), UDP-Glc (♦), UDP-GalNAc (***), UDP-GalUA (○), and UDP-Gal (□).