|Alternate Names:||CYC, CYCS|
|Structure and Function:||
Cytochrome c is a water-soluble mitochondrial intermembrane-space protein loosely attached to the inner mitochondrial membrane. It is approximately 13 kDa. It plays important roles in two processes: oxidative phosphorylation and apoptosis.
As an electron carrier in oxidative phosphorylation, cytochrome c shuttles four electrons, one at time, via its heme group from Complex III (cytochrome c reductase) to Complex IV (cytochrome c oxidase).
As a crucial player in apoptosis (programmed cell death), cytochrome c is released from the mitochondria to the cytosol where it binds to an adaptor subunit, APAF-1 in the presence of dATP, leading to activation of caspase 9. Caspase 9 triggers activation of other caspases which cleave and destroy other proteins. This results in cell death.
Defects in CYCS are the cause of thrombocytopenia type 4 (THC4) [MIM:612004]; also known as autosomal dominant thrombocytopenia type 4.
Because cytochrome c leaves the apoptotic cell following induction of apoptosis it is being increasingly recognized as a potentially useful circulating extracellular diagnostic and prognostic biomarker for disease conditions in which apoptosis is involved.
Review of potential cytochrome c biomarker applications.