<unk>  (abbreviated<unk> ,<unk> , infrequently<unk> 450) is a very large and diverse superfamily of hemoproteins found in all domains of life. <unk>  use a plethora of both exogenous and endogenous compounds as substrates in enzymatic reactions. Usually they form part of multicomponent electron transfer chains, called<unk> -containing systems.
The most common reaction catalysed by<unk>  is a monooxygenase reaction, e.g. insertion of one atom of oxygen into an organic substrate (RH) while the other oxygen atom is reduced to water:
RH + O2 + 2H+ + 2e– → ROH + H2O<unk>  enzymes have been identified from all lineages of life, including mammals, birds, fish, insects, worms, sea squirts, sea urchins, plants, fungi, slime molds, bacteria and archaea. More than 7700 distinct<unk>  sequences are known (as of September 2007; see the web site of the<unk>  Nomenclature Committee for current counts).
The name<unk>  is derived from the fact that these are colored ('chrome') cellular ('cyto') proteins, with a "pigment at 450 nm", so named for the characteristic Soret peak formed by absorbance of light at wavelengths near 450 nm when the heme iron is reduced (often with sodium dithionite) and complexed to carbon monoxide.
Cytochrome P450
Caspase
Cytochrome c oxidase
Aminotransferases
Cytochrome b559
Ubiquinol oxidase
Enzyme
Transaminase