Oxidation-reduction behavior of the heme c and heme d moieties of Pseudomonas aeruginosa nitrite reductase and the formation of an oxygenated intermediate at heme d1.

Dithionite reduced the heme c moiety of Pseudomonas nitrite reductase almost instantaneously, whereas the spectral change of heme d proceeded in two steps, requiring at least 15 min for completion. The final spectrum coincided well with that obtained by anaerobic reduction with ascorbate, during which a quasi oxidation-reduction equilibrium was established between the two heme groups. The difference in apparent redox potential was calculated to be 24 mV, heme d being more negative. When the enzyme was supplemented with a reductant and molecular oxygen, an oxygenated intermediate appeared at the heme d moiety.