The pH profile and the effects of metal ions, EDTA, and DTT on the α2,3-sialyltransferase activity of Hd0053 by quantitative HPLC analysis. (A) The pH profile. Activity was measured at indicated pH at 37 °C for 60 min. Buffers (200 mM) used were: MES, pH 5.0−6.0; Hepes, pH 7.0; Tris–HCl, pH 7.5−9.0; and CAPS, pH 10−11. (B) Effects of metal ions, EDTA, and DTT. The activity was determined in Tris-HCl buffer (100 mM, pH 8.5) at 37 °C for 60 min.