Ubiquinone is an essential component of the electron transport chain in mammals and most bacteria and participates in aerobic cellular respiration.1-3 Lipoquinone function in membrane systems has been widely studied, and the exact location and conformation within membranes remains controversial. In this study, we determined the location, orientation, and conformation of ubiquinone-2 (UQ-2), a truncated analog of UQ-10, in model membrane system to compare the results to previously studied MK-2. We carried out a series of 1H-1H 2D NOESY and ROESY NMR spectroscopic studies that demonstrated that UQ-2 adopts a folded conformation in polar and non-polar organic solvents, as well as in AOT reverse micelles, a model membrane system (Figure 1). In all four solvents examined in this study (DMSO, acetonitrile, pyridine, and benzene), UQ-2 was found to adopt a folded, U-shaped conformation.3 On the other hand, UQ-2 adopts a more open U-shaped conformation in the hydrophobic solvents, benzene and pyridine, which documents the fact that the environment will impact the conformation of the UQ-2 side chain.3 The conformations of the truncated analog, UQ-2, can be compared to ubiquinone-10, a cofactor in the eukaryotic electron transport chain. The differences in conformation within the cellular membrane likely impact reactivity of UQ-10 in vital cellular redox processes.

Ubiquinone-2 adopts a folded, u-shaped conformation in the respiratory complex

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