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Evidence for two H 2 O 2 ‐binding sites in ferric cytochrome c oxidase Indication to the O‐cycle?
Author(s) -
Vygodina Tatyana,
Konstantinov Alexander A.
Publication year - 1987
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(87)80258-2
Subject(s) - chemistry , cytochrome c oxidase , heme , oxidase test , ligand (biochemistry) , stereochemistry , cytochrome , absorption (acoustics) , redox , ferric , enzyme , crystallography , photochemistry , inorganic chemistry , biochemistry , receptor , physics , acoustics
H 2 O 2 addition to the oxidized cytochrome c oxidase reconstituted in liposomes brings about a red shift of the Soret band of the enzyme and an increased absorption in the visible region with two distinct peaks at ∼570 and 605 nm. Throughout pH range 6–8.5, the spectral changes at 570 nm and in the Soret band titrate with very similar pH‐independent K d values of 2–3,μM. At the same time, K d of the peroxide complex measured at 605 nm increases markedly with increased H + activity reaching the value of 18 ± 2 μM at pH 6.0. This finding may indicate the presence of two different H 2 O 2 ‐binding sites in the enzyme with different affinity for the ligand at acid pH. The Soret and 570 nm band effects are suggested to report H 2 O 2 coordination to heme iron of a 3 , whereas the maximum at 605 nm could arise from H 2 O 2 binding to Cu a 3 followed by the enzyme transition into the ‘pulsed’ (or ‘420/605’) conformation. Possible implication of the two H 2 O 2 ‐binding sites for the cytochrome oxidase redox and proton‐pumping mechanisms are discussed.