Cytochromes P460 are small, monoheme enzymes found in diverse classes of bacteria including ammonia oxidizers, methane oxidizers, and denitrifiers. They are named for their metallocofactor, heme P460, which is a highly ruffled c-heme that in the cases of cytochromes P460, feature a covalent heme-lysine cross-link in addition to canonical covalent thioether linkages. Although their exact physiological role(s) remain uncertain, it has been demonstrated that these enzymes are capable of oxidation of hydroxylamine to nitrous oxide via a ferric nitrosyl intermediate. This behavior differentiates these enzymes from the other heme P460-containing enzyme family, the hydroxylamine oxidoreductases (HAOs), which selectively oxidize hydroxylamine to nitric oxide as part of the primary metabolism of bacterial ammonia oxidizers. This lecture will discuss key molecular and electronic structural features of cytochromes P460 that give rise to their reactivity. Focus will be placed on the role of the heme-Lys cross-link, the mechanism by which it is installed, and the nature of the ferric nitrosyl intermediate.

Structure/function relationships underpinning cytochrome P460 redox catalysis

ACS Fall 2021

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