Open AccessThe physical state of ubiquinone‐10, in pure form and incorporated into phospholipid bilayers
Author(s) -
CASTRESANA José,
ALONSO Alicia,
ARRONDO JoséLuis R.,
GOÑI Félix M.,
CASAL Héctor
Publication year - 1992
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1992.tb16737.x
Subject(s) - thermotropic crystal , phospholipid , membrane , phase (matter) , isotropy , bilayer , chemistry , crystallography , liquid crystal , lipid bilayer , phase transition , chemical physics , liquid crystalline , organic chemistry , materials science , thermodynamics , biochemistry , optics , physics , optoelectronics
Long‐chain quinones are essential components of both bacterial and eukaryotic respiratory chains, and some of the main unsolved questions on energy transduction in membranes are complicated by the lack of consistent information on the physical state of the quinones in membrane bilayers. We have recorded, at various temperatures and under different conditions, the infrared spectra of ubiquinone‐10 (the main species in mitochondria) and several analogues. The C = O stretching vibration band located at 1663–1670 cm −1 has been identified as the most sensitive one to phase and environmental changes. Three distinct phases have been characterized in which pure ubiquinone‐10 may exist: crystalline (LC 1 ), isotropic liquid (I L ) and liquid crystalline (L c ). The only allowed thermotropic transitions are LC 1 → I L , I L → L c and L c → LC 1 . Our investigations with pure quinones provide a simpler and more detailed description of their phase changes than any of the previous studies and shed light on their behaviour in membranes. When incorporated into phospholipid bilayers, ubiquinone‐10 appears to be removed from the aqueous environment and is found to exist, in the 4–70°C range, in an isotropic liquid phase, in the form of small aggregates.