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Probing the access of protons to the K pathway in the Paracoccus denitrificans cytochrome c oxidase
Author(s) -
Richter OliverM. H.,
Dürr Katharina L.,
Kannt Aimo,
Ludwig Bernd,
Scandurra Francesca M.,
Giuffrè Alessandro,
Sarti Paolo,
Hellwig Petra
Publication year - 2005
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2004.04480.x
Subject(s) - paracoccus denitrificans , heme a , chemistry , cytochrome c oxidase , protonation , deprotonation , heme , electron transport complex iv , stereochemistry , redox , enzyme , photochemistry , biochemistry , inorganic chemistry , organic chemistry , ion
In recent studies on heme‐copper oxidases a particular glutamate residue in subunit II has been suggested to constitute the entry point of the so‐called K pathway. In contrast, mutations of this residue (E78 II ) in the Paracoccus denitrificans cytochrome c oxidase do not affect its catalytic activity at all (E78 II Q) or reduce it to about 50% (E78 II A); in the latter case, the mutation causes no drastic decrease in heme a 3 reduction kinetics under anaerobic conditions, when compared to typical K pathway mutants. Moreover, both mutant enzymes retain full proton‐pumping competence. While oxidized‐minus‐reduced Fourier‐transform infrared difference spectroscopy demonstrates that E78 II is indeed addressed by the redox state of the enzyme, absence of variations in the spectral range characteristic for protonated aspartic and glutamic acids at ≈ 1760 to 1710 cm −1 excludes the protonation of E78 II in the course of the redox reaction in the studied pH range, although shifts of vibrational modes at 1570 and 1400 cm −1 reflect the reorganization of its deprotonated side chain at pH values greater than 4.8. We therefore conclude that protons do not enter the K channel via E78 II in the Paracoccus enzyme.