Cytochrome C is an inner mitochondrial membrane hemeprotein encoded by CYCS gene. Cytochrome C has two major roles within the cell; firstly, it acts as an electron carrier between Complex III (Cytochrome bc1 complex) and Complex IV (Cytochrome C oxidase). The second important function of Cytochrome C is in apoptosis. In response to extrinsic or intrinsic signals and upon suppression of anti-apoptotic molecules, several pro-apoptotic molecules are activated that disturb the mitochondrial membrane permeability and causes the release of Cytochrome C. Cytochrome C then binds to apoptotic protease activating factor-1 (Apaf-1). This complex interacts with pro-caspase 9 and initiates the caspase cascade resulting in apoptosis. Human Cytochrome C has a molecular mass of 11 kDa. Defect in the CYCS gene is associated with autosomal dominant diseases like thrombocytopenia type 4 (THC4). High levels of Cytochrome C are found in blood leukocytes, kidney, liver, heart and brain.