Table 1. Activity and selectivity of wild-type UAXS and variant enzymes for conversion of UDP-GlcA (2).

Enzyme	kcat[a] [min-1]	UDP-apiose (1a) [%]	UDP-xylose (3) [%]	UDP-4-keto-xylose[b] (5) [%]	Apiose cyclic 1,2-phosphate (1) [%]
Wild-type	0.49	59	26	8	7
Y185F	0	n.a.	n.a.	n.a.	n.a.
Y105F	0.05	18	41	32	9
Y105A	0.13	0	50	50	0
T139V	3 × 10-3	0	0	100	0
C100A	0.12	18	61	15	6
C100S	0.09	0	21	79	0
C140S	0.07	29	26	35	10
C140A	0.11	15	33	52	0
C100A/C140S	0.23	27	32	33	8
E141A	3 × 10-3	0	0	100[b]	0

^[a]Activity (k_cat) was measured by HPLC-UV as depletion of substrate in H₂O at pH 7.0 (Supplementary Figures 17-32). Selectivity for product formation was determined by ¹H-NMR in D₂O (pD 7.0) (Supplementary Figure 33-35). Reaction conditions: 50 mM potassium phosphate buffer; 30 °C; 2 mM substrate; 0.1 mM NAD⁺ (1.0 mM for T139V and E141A variants). An appropriate enzyme concentration between 0.5 and 14.3 mg/mL was used. Note: there was no solvent isotope effect on the k_cat (see Supplementary Figure 36). n.a. = not applicable. Data are from multiple determinations have relative S.D. ≤ 10% (except Y105F, 20%; see Supplementary Figures 17-32).

^[b]22 mg/mL enzyme added for ¹H-NMR measurement.