performed the glycosylation of 2 with the sugar phosphate a' to confirm that the higher reaction pH did not inhibit the second reaction step (reverse phosphorolysis). We observed no significant difference in glycosylation activity at pH 7 or 9, indicating that the deprotonated Se-base is well-accepted by the enzyme (Figure ). Taken together, these data show that a reaction pH of 9 improves the solubility of 1 and 2 and thus permits higher substrate loadings, while still allowing excellent enzymatic activity, with reaction temperatures of 60 °C or 80 °C presumably facilitating additional solubility.