Individual heme a and heme a3 contributions to the Soret absorption spectrum of the reduced bovine cytochrome c oxidase

• Published in: Biochimica et biophysica acta. Bioenergetics 2023-04, Vol.1864 (2), p.148937-148937, Article 148937
• Main Authors: Diuba, Artem V., Vygodina, Tatiana V., Azarkina, Natalia V., Arutyunyan, Alexander M., Soulimane, Tewfik, Vos, Marten H., Konstantinov, Alexander A.
• Format: Article
• Language: English
• Subjects: Absorption spectra; Biochemistry, Molecular Biology; Cytochrome c oxidase; Femtosecond pump-probe spectroscopy; Life Sciences
• ISSN: 0005-2728; 1879-2650
• DOI: 10.1016/j.bbabio.2022.148937

Bovine cytochrome c oxidase (CcO) contains two hemes, a and a3, chemically identical but differing in coordination and spin state. The Soret absorption band of reduced aa3-type cytochrome c oxidase consists of overlapping bands of the hemes a2+ and a32+. It shows a peak at ∼444 nm and a distinct shoulder at ∼425 nm. However, attribution of individual spectral lineshapes to hemes a2+ and a32+ in the Soret is controversial. In the present work, we characterized spectral contributions of hemes a2+ and a32+ using two approaches. First, we reconstructed bovine CcO heme a2+ spectrum using a selective Ca2+-induced spectral shift of the heme a2+. Second, we investigated photobleaching of the reduced Thermus thermophilus ba3- and bovine aa3-oxidases in the Soret induced by femtosecond laser pulses in the Q-band. The resolved spectra show splitting of the electronic B0x-, B0y-transitions of both reduced hemes. The heme a2+ spectrum is shifted to the red relative to heme a32+ spectrum. The ∼425 nm shoulder is mostly attributed to heme a32+. [Display omitted] •Bovine CcO a2+ Soret band is a split electronic 447.5-nm peak with a minimal short-wavelength satellite.•a2+ α-band is also split.•a32+ Soret band is a split electronic 441-nm peak with a short-wavelength satellite.•Ratio of integrals under a2+ and a32+ Soret bands is approximately 1 to 2.