. Author manuscript; available in PMC: 2008 Oct 1.

Published in final edited form as: Biochemistry. 2006 Jun 20;45(24):7415–7428. doi: 10.1021/bi060152s

Table 3.

Kinetic constants for alternate substrates

Substrate	Parameter	Wt TS	Y261F	Y261A
dUMP	K_m, μM	6+/- 2	6.6+/- 0.6	34+/- 6
dUMP	k_cat, s^-1	3.8+/- 0.2	1.7+/- 0.04	0.026+/- 0.001
UMP	K_m, μM	1165+/-136	1411+/- 101	n.d.^a
	k_cat, s^-1	2.5+/- 0.1	0.022+/- .001	n.d.
	Selectivity^b	5.7+/- 0.4	9.7+/- 0.1	—
ddUMP	K_m, μM	836+/- 143	1630+/- 216	n.d.
	k_cat, s^-1	1.17+/- 0.07	1.07+/- 0.06	n.d.
	Selectivity	6.1+/- 0.4	6.0+/- 0.2	—

n.d.= no detectable activity

Selectivity = ln[(k_cat/K_m^dUMP)/( k_cat/K_m^x)], where x=UMP or ddUMP