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The role of tryptophan 272 in the Paracoccus denitrificans cytochrome c oxidase
Author(s) -
MacMillan Fraser,
Budiman Kerstin,
Angerer Heike,
Michel Hartmut
Publication year - 2006
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/j.febslet.2006.01.054
Subject(s) - paracoccus denitrificans , electron paramagnetic resonance , catalytic cycle , chemistry , electron transfer , stereochemistry , cytochrome c oxidase , electron paramagnetic resonance spectroscopy , photochemistry , tyrosine , tryptophan , active site , enzyme , crystallography , biochemistry , nuclear magnetic resonance , amino acid , physics
The mechanism of electron coupled proton transfer in cytochrome c oxidase (C c O) is still poorly understood. The P M ‐intermediate of the catalytic cycle is an oxoferryl state whose generation requires one additional electron, which cannot be provided by the two metal centres. The missing electron has been suggested to be donated to this binuclear site by a tyrosine residue. A tyrosine radical species has been detected in the P M and F intermediates (formed by addition of H 2 O 2 ) of the Paraccocus denitrificans C c O using electron paramagnetic resonance (EPR) spectroscopy. From the study of conserved variants its origin was determined to be Y167 which is surprising as this residue is not part of the active site. Upon inspection of the active site it becomes evident that W272 could be the actual donor of the missing electron, which can then be replenished from Y167 or from the Y280‐H276 cross link in the natural cycle. To address the question, whether such a direct electron transfer pathway to the binuclear centre exists two tryptophan 272 variants in subunit I have been generated. These variants are characterised by their turnover rates as well as using EPR and optical spectroscopy. From these experiments it is concluded, that W272 is an important intermediate in the formation of the radical species appearing in P M and F intermediates produced with hydrogen peroxide. The significance of this finding for the catalytic function of the enzyme is discussed.