Morphology of proteoliposomes containing fluorescein-phosphatidylethanolamine reconstituted with native and subunit III-depleted cytochromec oxidase

Beef heart cytochromec oxidase was reconstituted in asolectin liposomes containing the pH indicator fluorescein-phosphatidylethanolamine (FPE) by the cholate-dialysis procedure. The influence of PFE 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 homogenous, 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 (>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.Dedicated to the memory of Dr. R. P. Casey.