Electron nuclear double resonance (ENDOR) of the Qc.- ubisemiquinone radical in the mitochondrial electron transport chain.
We present an electron nuclear double resonance (ENDOR) study of the bound Qc.- ubisemiquinone in the mitochondrial quinol cytochrome c reductase complex. An ENDOR probe specifically modified for insertion into our electron paramagnetic resonance cavity was used for this study. We observed strongly hyperfine-coupled protons whose exchangeable nature indicated they were hydrogen-bonded to the quinone oxygen(s). It is thought that such hydrogen bonds are critical in binding the ubiquinone to protein, in stabilizing its semiquinone form, and in modulating the thermodynamic properties of the bound ubiquinone in the mitochondrial quinol cytochrome c reductase complex. Additional ENDOR features were assigned to protons of the quinone ring itself and to weakly coupled protons that may be associated with nearby amino acids. From very weakly hyperfine-coupled, distant, exchangeable protons there was also ENDOR evidence to suggest proximity and accessibility of the ubiquinone site to the solvent.
Salerno
J C
JC
Department of Biology, Rensselaer Polytechnic Institute, Troy, New York 12180.
Osgood
M
M
Liu
Y J
YJ
Taylor
H
H
Scholes
C P
CP
D000818:Animals; D001665:Binding Sites; D002417:Cattle; D003067:Coenzymes; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D005609:Free Radicals; D006860:Hydrogen Bonding; D066298:In Vitro Techniques; D009682:Magnetic Resonance Spectroscopy; D008929:Mitochondria, Heart / Q000378:metabolism*; D014451:Ubiquinone / Q000737:chemistry / Q000378:metabolism* / Q000031:analogs & derivatives
D003067:Coenzymes; D005609:Free Radicals; D014451:Ubiquinone; C024989:coenzyme Q10