Influence of membrane fluidity on transport mediated by ubiquinones through phospholipid vesicles

Coenzymes Q10 and Q3 are incorporated into dipalmitoylphosphatidylcholine and egg yolk lecithin liposomes. Dithionite reduction of ferricyanide trapped inside these phospholipid vesicles is taken as a measure of ubiquinone-mediated transport of reducing equivalents. The reaction shows complex pattern with a high order for CoQ. The initial transport rates are very sensitive to the membrane physical state, being considerably reduced at temperatures below the phase transition of the pure dipalmitoylphosphatidylcholine, both for CoQ10 and CoQ3 reconstituted with this phospholipid. It is suggested that a different reaction mechanism operates in fluid and rigid membranes. This suggestion is related to the possible organization of CoQs in phospholipid membranes.