Isolation and characterization of the d(1) domain of Pseudomonas aeruginosa nitrite reductase

Proteolitic digestion of nitrite reductase from Pseudomonas aeruginosa allows to obtain and purify a domain containing only the d(1) heme and constituted by two noncovalently bound peptides. This d(1) domain catalyzes oxygen consumption, and binds carbon monoxide with a kinetic constant slightly higher than the parental dimeric holoenzyme. The capacity to oxidize the physiological substrate, cytochrome c(551), is lost, even when the proteolytic c heme domain is added to this reaction mixture. This finding suggests that the two domains do not have a significant affinity for each other, and are kept together only by being part of the same polypeptide.