Because cytochrome c plays a major role in apoptosis, its measurement can lead to greater understanding of certain diseases on a cellular level. Cytochrome c is an essential component of the mitochondrial respiratory chain. It is a soluble protein that is localized in the intermembrane space and loosely attached to the surface of the inner mitochondrial membrane. Cytochrome c is important to the process of creating cellular energy, the main function of mitochondria. When mitochondria are damaged, cytochrome c is released into the main body of the cell and, if the cell itself is damaged, into the surrounding tissue. The release of cytochrome c is part of the cascade of cellular events that leads to apoptosis, or programmed cell death. When the cycle that leads to apoptosis begins, cytochrome c appears outside the mitochondria within one hour.


