Table 1.

Determined kinetic constants for the selenophosphate synthetase enzymes

Selenophosphate synthetase	Km ATP, mM	Km selenide, μM	Specific activity, nmol/min per mg
E. coli	0.9	20	29
H. influenzae	1.3	25	16

Reactions were performed anaerobically at 37°C. Reaction mixtures (0.1 ml) contained 100 mM Tricine⋅KOH (pH 7.8), 2 mM DTT, 20 mM KCl, 4 mM MgCl₂, 5 μM selenophosphate synthetase, and the appropriate concentration of substrate.