Morphology of proteoliposomes containing fluorescein-phosphatidylethanolamine reconstituted with native and subunit III-depleted cytochrome c oxidase.

Beef heart cytochrome c oxidase was reconstituted in asolectin liposomes containing the pH indicator fluorescein-phosphatidylethanolamine (FPE) by the cholate-dialysis procedure. The influence of FPE on the asolectin liposome size and of the removal of subunit III from the complex on its incorporation into liposomes was analyzed by freeze-fracture electron microscopy. Samples were frozen without the addition of cryoprotectants. The vesicle size distribution of native enzyme reconstituted into asolectin liposomes was homogeneous, 84% of the population having a diameter of 14-37 +/- 7.5 mm. The preparation containing FPE had a similar vesicle size distribution, but with bigger diameter range (20-50 nm). In all three different types of proteoliposome preparations the majority of particles containing vesicles was found to have 1 particle (42-81%). The absence of subunit III did not influence the incorporation of the enzyme into the liposomes and was as good as the preparation with native enzyme (greater than 99%). Therefore we conclude that the suppression of the proton pump activity was due to the intrinsic properties of subunit III and not to defective incorporation into artificial membrane systems.