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Resonance Raman evidence for an exchangeable protein hydrogen associated with the heme a group of cytochrome oxidase
Author(s) -
Copeland Robert A.,
Spiro Thomas G.
Publication year - 1986
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(86)80334-9
Subject(s) - heme a , chemistry , heme , cytochrome c oxidase , cytochrome , hemeprotein , photochemistry , cytochrome c , resonance raman spectroscopy , raman spectroscopy , redox , resonance (particle physics) , stereochemistry , enzyme , biochemistry , inorganic chemistry , particle physics , physics , optics , mitochondrion
When cytochrome– c oxidase is soaked in D 2 O, downshifts of the cytochrome a formyl C=O stretching mode are seen in the resonance Raman (RR) spectra (413.1 nm excitation) of both the resting and reduced forms. Other changes observed in the reduced protein RR spectra are consistent with involvement of the cytochrome a formyl group in the deuterium effect. The D 2 O–induced RR changes are fully developed during 3–5 days incubation, but are incomplete after 1 h. Extraction of the heme a chromophore in deuterated solvents eliminates these changes, implying that the exchangeable proton is on a protein group in the cytochrome a pocket which H–bonds to the heme formyl. The rate of the D 2 O exchange process is unaffected by enzyme turnover, thus reducing the likelihood that the cytochrome a formyl H–bond is directly involved in the redox–linked mechanism of proton pumping.