Table 2.

Effect of H₂O₂ on the catalytic activity of selenophosphate synthetase enzymes

[H2O2], mM	E. coli selenophosphate synthetase activity, %	H. influenzae selenophosphate synthetase activity, %
0	100	100
2.5	71	63
5	56	47
10	38	46

Reaction mixtures contained 100 mM Tricine⋅KOH (pH 7.8), 2 mM DTT, 6 mM MgCl₂, 20 mM KCl, 30 μM selenophosphate synthetase, and the indicated concentration of H₂O₂. Samples were incubated at room temperature for 30 min. Reactions were quenched by applying the mixtures to PD10 columns equilibrated in buffer A. Equilibrated protein was used directly in the selenophosphate synthetase assay (4).