Cytochrome c is an electron-carrying mitochondrial protein. It is a small heme protein containing a single polypeptide chain and a single heme group, which is covalently attached to the polypeptide. The ready fluctuation of cytochrome c within the cell between ferrous and ferric states makes it an efficient biological electron-transporter and it plays a vital role in cellular oxidations in both plants and animals. It is generally regarded as a universal catalyst of respiration, forming the essential electron-bridge between the respirable substrates and oxygen.