Types
Several kinds of cytochrome exist and can be distinguished by spectroscopy, exact structure of the heme group, inhibitor sensitivity, and reduction potential.
Three types of cytochrome are distinguished by their prosthetic groups:
| Type | prosthetic group |
| Cytochrome a | heme a |
| Cytochrome b | heme b |
| Cytochrome d | tetrapyrrolic chelate of iron |
The definition of cytochrome c is not defined in terms of the heme group. There is no "cytochrome e," but there is a cytochrome f, which is often considered a type of cytochrome c.
In mitochondria and chloroplasts, these cytochromes are often combined in electron transport and related metabolic pathways:
| Cytochromes | Combination |
| a and a3 | Cytochrome c oxidase ("Complex IV") with electrons delivered to complex by soluble cytochrome c (hence the name) |
| b and c1 | Coenzyme Q - cytochrome c reductase ("Complex III") |
| b6 and f | Plastoquinol—plastocyanin reductase |
A completely distinct family of cytochromes is known as the cytochrome P450 oxidases, so named for the characteristic Soret peak formed by absorbance of light at wavelengths near 450 nm when the heme iron is reduced (with sodium dithionite) and complexed to carbon monoxide. These enzymes are primarily involved in steroidogenesis and detoxification.
Read more about this topic: Cytochrome
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