Splitting of the O-O bond at the heme-copper catalytic site of respiratory oxidases

• Published in: Science advances 2017-06, Vol.3 (6), p.e1700279-e1700279
• Main Authors: Poiana, Federica, von Ballmoos, Christoph, Gonska, Nathalie, Blomberg, Margareta R A, Ädelroth, Pia, Brzezinski, Peter
• Format: Article
• Language: English
• Subjects: Biochemistry; biokemi; SciAdv r-articles
• ISSN: 2375-2548; 2375-2548
• DOI: 10.1126/sciadv.1700279

Heme-copper oxidases catalyze the four-electron reduction of O to H O at a catalytic site that is composed of a heme group, a copper ion (Cu ), and a tyrosine residue. Results from earlier experimental studies have shown that the O-O bond is cleaved simultaneously with electron transfer from a low-spin heme (heme a/b), forming a ferryl state ( ; Fe =O , Cu -OH ). We show that with the ba oxidase, at low temperature (10°C, pH 7), electron transfer from the low-spin heme b to the catalytic site is faster by a factor of ~10 (τ ≅ 11 μs) than the formation of the ferryl (τ ≅110 μs), which indicates that O is reduced before the splitting of the O-O bond. Application of density functional theory indicates that the electron acceptor at the catalytic site is a high-energy peroxy state [Fe -O -O (H )], which is formed before the ferryl. The rates of heme b oxidation and ferryl formation were more similar at pH 10, indicating that the formation of the high-energy peroxy state involves proton transfer within the catalytic site, consistent with theory. The combined experimental and theoretical data suggest a general mechanism for O reduction by heme-copper oxidases.