Femtosecond Absorption Spectroscopy of Reduced and Oxidized Forms of Cytochrome c Oxidase: Excited States and Relaxation Processes in Heme a and a3 Centers
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Excited electronic states and intraheme relaxation processes in the oxidized and reduced forms of mitochondrial cytochrome c oxidase extracted from a beef heart have been investigated by femtosecond absorption spectroscopy. The spectral and kinetic characteristics of short-lived intermediates have been measured from 80 fs to 20 ps after the photoexcitation. It is found that nonradiative electronic relaxation of the excitation energy in heme a, both in the oxidized (Fe(III)a) and reduced (Fe(II)a) forms, occurs successively as three processes, after the end of which heme a is in the ground state with a large store of vibrational energy. The subsequent vibrational relaxation (heme cooling) lasts for several picoseconds. It is found for reduced heme a3 (Fe(II)a3) that the electronic relaxation occurs as a result of two successive stages, which changes to vibrational relaxation in the ground state. The mechanism and dynamics of electronic excitation energy conversion in cytochrome c oxidase are analyzed.
Keywords:cytochrome c oxidase femtosecond absorption spectroscopy excited electronic states relaxation processes spectral intermediates
We are grateful to A.A. Konstantinov and A.F. Chaikovskii for their interest in this study and valuable remarks.
This study was supported by the State Research Program “Photonics and Opto- and Microelectronics 1.4.01” (2016–2020) of the Republic of Belarus, Russian Foundation for Basic Research (project no. 17-04-00160a), and a grant for the Semenov Institute of Chemical Physics, Russian Academy of Sciences, within state contract 0082-2019-0001 (registration no. AAAA-A19-119012890064-7).
CONFLICT OF INTEREST
The authors declare that they have no conflict of interest.
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