Structural characteristics and redox activity of the cubic monoolein/ubiquinone-10/water phase

Abstract

Ubiquinone-10 (UQ₁₀), a mitochondrial carrier of electrons and protons, has been entrapped in a bicontinuous Pn3m cubic phase of monoolein (MO) and water (W) at a concentration of 0.34 mol% with respect to MO. X-ray diffraction, FT-IR and cyclic voltammetry techniques have been used to study the crystallographic structure, molecular features and redox activity of the cubic MO/UQ₁₀/W phase of 60.8:0.5:38.7 wt% composition compared to the cubic MO/W phase of 61:39 wt% composition. The X-ray data indicate that this low amount of UQ₁₀ leaves the crystallographic structure of the Pn3m cubic phase unaltered (the lattice parameters were 96.8±2.2 and 98.1±0.5 Å for the binary and ternary systems, respectively). According to the FT-IR spectroscopy measurements, the acyl chains of MO in the both cubic phases contain similar types and concentrations of nonplanar (gauche) conformers. The headgroup-sensitive features of the FT-IR spectra also indicate that the MO bilayer arrangement is similar in the binary and ternary cubic phases. The cyclic voltammograms of the gold electrode coated by the cubic MO/UQ₁₀/W phase show that the entrapped UQ₁₀ undergoes electrochemically irreversible UQ₁₀/UQ₁₀H⁻ transition over the pH range from 6 to 8. The diffusion coefficient of the coenzyme was determined to 1.9×10⁻⁸ cm²/s by the same technique. The location and redox function of UQ₁₀ in the cubic phase are discussed on the basis of the obtained electrochemical results.

In honour of Professor K. Larsson on the occasion of his 60th birthday