Structural Characterization of Cytochrome from an Ammonia-Oxidizing Bacterium.

The ammonia-oxidizing bacterium expresses two cytochromes in the P460 superfamily that are predicted to be structurally similar. In one, cytochrome (cyt) P460, the substrate hydroxylamine (NHOH) is converted to nitric oxide (NO) and nitrous oxide (NO) requiring a unique heme-lysyl cross-link in the catalytic cofactor. In the second, cyt , the cross-link is absent, and the cytochrome instead binds HO forming a ferryl species similar to compound II of peroxidases.

Cytochrome ' Is a Variant in the P460 Superfamily Lacking the Heme-Lysyl Cross-Link: A Peroxidase Mimic Generating a Ferryl Intermediate.

A defining characteristic of bacterial cytochromes (cyt's) in the P460 family is an unusual cross-link connecting the heme porphyrin to the side chain of a lysyl residue in the protein backbone. Here, via proteomics of the periplasmic fraction of the ammonia-oxidizing bacterium (AOB) , we report the identification of a variant member of the P460 family that contains a methionyl residue in place of the cross-linking lysine. We formally designate this protein cytochrome "'" to distinguish it from other members bearing different residues at this position (e.