Cytochrome

Definition

Any of a class of redox-active proteins containing a heme cofactor with a central iron atom, functioning as electron carriers in metabolic pathways including the electron transport chain. Cytochromes are classified by heme type (a, b, c, or d) and binding mode, and are essential to oxidative phosphorylation, detoxification, and P450-mediated metabolism.

Etymology

From Greek kytos (cell) + chrōma (color), referring to their pigmented heme groups.

Example

Cytochrome P450 monooxygenases in insects metabolize plant allelochemicals and synthetic insecticides; elevated cytochrome P450 activity is a major mechanism of pyrethroid resistance in Anopheles mosquitoes and Heliothis moths.

Related Terms

• electron transport chain
• heme
• oxidative phosphorylation
• cytochrome P450
• mitochondrion
• respiration
• detoxification

Usage Notes

The term encompasses diverse functional classes; cytochrome c is a conserved electron shuttle between complexes III and IV, while cytochrome P450s constitute a large superfamily of enzymes involved in xenobiotic metabolism. In arthropod toxicology, 'cytochrome' often specifically references P450s when discussing resistance. Distinct from hemoglobin and myoglobin despite shared heme chemistry.