Activation volumes for intramolecular electron transfer in bovine heart cytochrome c oxidase

摘要

>The present work examines the activation volumes associated with intramolecular electron transfer (ET) within the CO-mixed-valence form of bovine heart cytochrome c oxidase (CcO). Activation volumes for intramolecular ET between cytochrome a ₃ and cytochrome a (k=(6.7±0.9)×105 s−1 at ambient pressure) and between cytochrome a and Cu_A (k=(5.9±1.7)×104 s−1) are found to be +41±5 ml/mol and +28±4 ml/mol, respectively. Examination of the crystal structures of both the fully oxidized and fully reduced forms of bovine heart CcO suggest that the activation volume for the ET between cytochrome a ₃ and cytochrome a arises from structural changes localized at cytochrome a ₃ upon heme reduction. Similarly, the activation volume for the ET between cytochrome a and Cu_A is primarily due to structural changes localized at Cu_A upon reduction of this site. Reduction/oxidation of cytochrome a does not appear to make any significant contribution to the activation volume. Overall, these results suggest conformational regulation of ET by both Cu_A and cytochrome a ₃ but not cytochrome a.