Table 2.

Steady state kinetic parameters of the WT and Y209W ecTSase at 25 °C. The value in the parenthesis below each number is the magnitude of that value relative to the corresponding WT parameter.

TSase	kcat (s−1)	$K_m^{\text{dUMP}}$	$K_m^{{\text{CH}}_2{\text{H}}_4\text{folate}}$	$K_m^{\text{dUMP}}/K_m^{{\text{CH}}_2{\text{H}}_4\text{folate}}$
WT w/β-MEa	8.8 (1)	4.1 ± 0.4 (1)	13.6 ± 0.2 (1)	0.30 (1)
Y209W w/β-MEa	0.05 ± 0.01 (0.005)	118 ± 40 (28.8)	172 ± 26 (12.6)	0.69 (2.3)
Y209W w/TCEP	0.020 ± 0.001 (0.002)	19 ± 2b (4.6)	214 ± 27 (15.7)	0.089 (0.30)

^aData from Ref 41. A comparison of WT activity with β-ME and with TCEP found no difference.

^bDetails shown in SI.