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Potentiometric titration of cytochrome‐ bo type quinol oxidase of Escherichia coli : Evidence for heme‐heme and copper‐heme interaction
Author(s) -
Salerno John C.,
Bolgiano Barbara,
Ingledew W.John
Publication year - 1989
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(89)81249-9
Subject(s) - cytochrome , heme , chemistry , cytochrome c oxidase , heme a , cytochrome c1 , cytochrome c peroxidase , cytochrome c , coenzyme q – cytochrome c reductase , cytochrome b , electron transport complex iv , hemeprotein , photochemistry , stereochemistry , biochemistry , enzyme , mitochondrion , mitochondrial dna , gene
The cytochrome‐ bo quinol oxidase of Escherichia coli contains a high‐spin b ‐type heme (cytochrome o ), a low‐spin b ‐type heme (cytochrome b ) and copper. The EPR signal from cytochrome o is axial high spin and when titrated potentiometrically gives a bell‐shaped curve. The low‐potential side of this curve ( E m7 approx. 160 mV) corresponds to the reduction/oxidation of the cytochrome. The high‐potential side ( E m7 approx. 350 mV) is proposed to be due to reduction/oxidation of a copper center; in the CuII form tight cytochrome o ‐copper spin coupling results in a net even spin system and loss of the EPR spectrum. Optical spectra of the α‐bands of the reduced cytochromes at 77 K show that cytochrome b has its maxima at 564 nm when cytochrome o is oxidized but that this shifts to 561 nm when cytochrome o (max. 555 nm) is reduced. Both a heme‐copper (cytochrome o ‐CuII) and a heme‐heme (cytochrome o ‐cytochrome b ) interaction are indicated in this quinol oxidase. These results indicate that cytochrome‐ bo quinol oxidase has a binuclear heme‐copper catalytic site and suggest striking structural similarity to subunit I of the cytochrome aa 3 system.