. Author manuscript; available in PMC: 2015 Apr 9.

Published in final edited form as: Chem Rev. 2014 Mar 3;114(7):3659–3853. doi: 10.1021/cr400327t

Table 31.

Midpoint Potentials of Cyt c and the Metal Sites of CcO (E_m values in mV).

	Cyt c	Cu_A	heme a	heme a₃	Cu_B	Ref
Isolated	283					⁹⁷¹
In mitochondria	235		205	390′		⁹⁷¹
Sub-mitochondria	235		205	365′		⁹⁷¹
Sub-mitochondria					340	⁹⁷³
In mitochondria			195			⁹⁷⁵
In mitochondria			220	380′		⁹⁷⁶
Isolated, Cyt c present		280	230	370′		⁹⁷⁴
Isolated, Cyt c present			210	340–350′		⁹⁷⁷
Isolated, TMPD present			215	340′		⁹⁶⁹
In mitochondria			high 362, low 238^*			⁹⁷⁸

When both heme sites are oxidized the E_m values of Cyt a and a₃ are similar (362 mV). Reduction of one heme lowers the E_m of the other to 238 mV.⁹⁷⁸ ′ Assuming heme a₃ gets reduced before heme a.