Table 2.

Comparative kinetic parameters of TMPKmt, TMPKec, and TMPKy with ATP and dTMP as substrates

TMPK	Km (ATP) (mM)	Km (dTMP) (μM)	Vm (ATP, dTMP) (μmole/min • mg of protein)	kcat (s−1)
M. tuberculosis	0.1	4.5	13	4.5
E. coli	0.04	15	50	10.5
Yeasta	0.19	9	84	35

^a Results from yeast were from Lavie et al. 1998a.

The reaction medium (0.5 mL final volume) contained 50 mM Tris-HCl pH 7.4, 50 mM KCl, 2 mM MgCl₂, 0.2 mM NADH, 1 mM phosphoenol pyruvate, and 2 units each of lactate dehydrogenase, pyruvate kinase and nucleoside diphosphate kinase. Activity was determined at 30°C as described under Materials and Methods. ATP was constant (0.2, 0.3, 0.4, and 0.7 mM) whereas the concentration of dTMP varied between 0.025 and 0.2 mM.