Kinetic study of the reaction of ebselen with peroxynitrite.

The second-order rate constant for the reaction of ebselen with peroxynitrite (ONOO-) is (2.0+/-0.1) X 10(6) M(-1) s(-1) at pH > or = 8 and 25 degrees C, 3-4 orders of magnitude higher than the rate constants observed for cysteine, ascorbate, or methionine. The activation energy is relatively low, 12.8 kJ/mol. This is the fastest reaction of peroxynitrite observed so far. It may allow Se-containing compounds to play a novel role in the defense against peroxynitrite, one of the important reactive species generated during inflammatory processes.