cytochrome P460 from Nitrosomonas europaea and similar proteins
Cytochrome (cyt) P460 is a small soluble periplasmic protein that binds the c-type heme cofactor, heme P460, named for its characteristic ferrous Soret peak maximum at 460 nm, which has the distinction of being the only known heme in biology to withdraw electrons from an iron coordinated substrate. The heme P460 in N. europea cyt P460 contains a third proteinaceous cross-link, similar to that found in hydroxylamine oxidoreductase (HAO), but in this case, the cross-link is to a conserved lysine residue, K70. The biological function of cyt P460 is yet to be determined, but it binds hydroxylamine, hydrazine, hydrogen peroxide, and cyanide in the ferric form, and CO in the ferrous form; it also possesses a weak hydroxylamine oxidation/cyt c reduction activity. It belongs to a family, called the cytochrome P460 family, of small mono-heme c-type cytochromes that are predominantly of beta-sheet structure, as opposed to the four elongate, tightly-packed alpha-helices of the widely distributed cytochromes c' of photoheterotrophic and denitrifying bacteria.