Peroxide-induced spectral perturbations of the 280-nm absorption band of cytochrome c oxidase

UV optical absorption by protein radicals in cytochrome c oxidase

The UV properties of key oxygen intermediates of cytochrome c oxidase have been investigated by transient absorption spectroscopy. The temporal behavior of P(m) species upon aerobic incubation with CO or in the reaction with H(2)O(2) is closely concurred by a new optical shift at 290/260 nm. In the acid-induced conversion of P(m) to F(*), it is replaced by another shift at 323/288 nm. The wavelength and intensity of the UV signal observed in F(*) match closely the properties of model Trp? in agreement with results of ENDOR studies on this species. The UV spectrum of Tyr* gives the closest match with the 290/260 nm signal observed in P(m). On the basis of analysis of possible UV chromophores in CcO and similarity to Tyr*, the 290/260 nm signal is proposed to originate from the H(240)-Y(244)* site. Possible effects of local environment on UV properties of this site are discussed.

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

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)x10(5) s(-1) at ambient pressure) and between cytochrome a and Cu(A) (k=(5.9+/-1.7)x10(4) 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.

Hydrogen peroxide is not released following reaction of cyanide with several catalytically important derivatives of cytochrome c oxidase

We have looked for the production of hydrogen peroxide following reaction of oxidized cytochrome c oxidase and two oxy derivatives (compounds P and F) with cyanide. In each case the final product was the cyanide adduct of cytochrome c oxidase. In no case release of hydrogen peroxide was detected, as gauged by the scopoletin plus horse radish peroxidase assay. The simplest conclusion is that none of these forms of the enzyme contains intact hydrogen peroxide.