text: Mitochondria play a central role in many other metabolic tasks, such as:
  * Signaling through mitochondrial reactive oxygen species
  * Regulation of the membrane potential
  * Apoptosis-programmed cell death
  * Calcium signaling (including calcium-evoked apoptosis)
  * Regulation of cellular metabolism
  * Certain heme synthesis reactions (see also: Porphyrin)
  * Steroid synthesis
  * Hormonal signaling – mitochondria are sensitive and responsive to hormones, in part by the action of mitochondrial estrogen receptors (mtERs). These receptors have been found in various tissues and cell types, including brain and heart
  * Immune signaling
  * Neuronal mitochondria also contribute to cellular quality control by reporting neuronal status towards microglia through specialised somatic-junctions.
  * Mitochondria of developing neurons contribute to intercellular signaling towards microglia, which communication is indispensable for proper regulation of brain development.
  Some mitochondrial functions are performed only in specific types of cells. For example, mitochondria in liver cells contain enzymes that allow them to detoxify ammonia, a waste product of protein metabolism. A mutation in the genes regulating any of these functions can result in mitochondrial diseases.
  Mitochondrial proteins (proteins transcribed from mitochondrial DNA) vary depending on the tissue and the species. In humans, 615 distinct types of proteins have been identified from cardiac mitochondria, whereas in rats, 940 proteins have been reported. The mitochondrial proteome is thought to be dynamically regulated.