The redox state influences the interaction of ubiquinones with phospholipid bilayers - A DSC study

Differential scanning calorimetry (DSC) has been used to study the interaction of ubiquinones (UQn) and their reduced forms, ubiquinols (UQnH(2)), with dipalmitoylphosphatidylcholine (DPPC) in multilamellar vesicles. The influence of the redox state has been investigated by comparing the effect of two ubiquinones with four (UQ4) and ten isoprene units (UQ10). In the presence of increasing amounts of UQ4 or UQ4H(2), concomitant shift of the gel to liquid crystalline phase transition towards lower temperatures and vanishing of the pre-transition are observed. Short-chain homologues are thus inserted parallel to phospholipid chains, their quinone ring close to the polar headgroups of the DPPC, with a larger degree of penetration for the reduced form. In addition, broadening and skewing of the main transition peak claim for a lateral self-organization in highly concentrated regions of UQ4 and UQ4H(2), with a redox state influence on the distribution in size and shape of lipid domains. The lipid thermotropic behavior is not affected by the presence of UQ10 which remain homogeneously dispersed within the midplane of the phospholipid bilayer, while effect of reduced UQ10H(2) argues for a different organization.