In the denitrification pathway, Pseudomonas aeruginosacytochrome cd1 nitrite reductase catalyzes the reduction of nitrite to nitric oxide;in vitro, this enzyme is also competent in the reduction of O2 to 2H2 O. In this art-icle, we present a comparative kinetic study of the O2 reaction in the wild-type nitrite reductase and in three site-directed mutants (Tyr10fiPhe, His369fiAla and His327fiAla⁄His369fiAla) of the amino acid resi-dues close to thed1 heme on the distal side.
