Electron carriers of cytochrome oxidase detectable by electron paramagnetic resonance and their relationship to those traditionally recognized in this enzyme.

On the basis of oxidoreductive rapid kinetic and titration experiments with purified cytochrome c oxidase (EC 1.9.3.1), monitored by electron paramagnetic resonance (EPR) at 13 degrees K and by spectrophotometry at 100 degrees K, a new assignment of EPR signals is proposed. The bulk of both the low-spin (g = 3.0; 2.2; 1.5) and highspin (g = 6; 2) signals is attributed to the component with the properties of traditional cytochrome a. It is further proposed that the absorption band at 655 nm represents the most unambiguous manifestation of the a(3) component.