Cytochrome c-cytochrome oxidase interaction at subzero temperatures.

Cytochrome oxidase forms two distinctive compounds with oxygen at --105 and --90 degrees C, one appears to be oxycytochrome oxidase (Compound A) and the other peroxycytochrome oxidase (Compound B). The functional role of compound B in the oxidation of cytochrome c has been examined in a variety of mitochondrial preparations. The rate and the extent of the reaction have been found to be dependent upon the presence of a fluid phase in the vicinity of the site of the reaction of cytochrome c and cytochrome oxidase. The kinetics of cytochrome c oxidation and of the slowly reacting component of cytochrome oxidase are found to be linked to one another even in cytochrome c depleted preparations, but under appropriate conditions, especially low temperatures, the oxidation of cytochrome c precedes that of this component of cytochrome oxidase. Based upon the identification of the slowly reacting components of cytochrome oxidase with cytochrome c, various mechanisms are considered which allow cytochrome c to be oxidized without the intervention of cytochrome a at very low temperatures, and tunneling seems an appropriate mechanism.