Ferritin-containing vesicles

However, this is not all as shown in the Figure 10.13, under certain conditions there is a small but significant concentration of small ferritin-containing vesicles of sizes that were not present before the addition of oleate. This clearly shows the process of division, as illustrated in Figure 10.11(b), process i. 

Figure 10.12 Number-weighted size distributions as obtained by cryo-TEM (adapted from Berclaz et al, 2001a, b). (a) Distribution for the pre-formed POPC vesicles ([POPC] = 1.9 mM). (b) Distribution for the vesicle suspension obtained upon addition of oleate to pre-formed ferritin-containing POPC vesicles ([POPC] = 0.2 mM [oleic acid -I- oleate] = 5 mM). Empty ( ) and ferritin-containing ( ) vesicles are represented individually in the histogram, (c) Direct comparison of the number-weighted size distribution of the pre-formed POPC vesicles, which contained at least one ferritin molecule ( ) with the number-weighted size distribution of the ferritin-containing vesicles obtained after oleate addition to pre-formed POPC vesicles ( ). Note that the total of all ferritin-containing vesicles was set to 100%.

Figure 10.10 Transmission electron micrograph of ferritin entrapped in POPC liposomes (palmitoyloleoylphosphatidylcholine). Cryo-TEM micrographs of (a) ferritin-containing POPC liposomes prepared using the reverse-phase evaporation method, followed by a sizing down by extrusion through polycarbonate membranes with 100 nm pore diameters ([POPC] = 6.1 mM) and (b) the vesicle suspension obtained after addition of oleate to pre-formed POPC liposomes ([POPC] = 3 mM, [oleic acid - - oleate] = 3 mM). (Adapted from Berclaz et al, 2001a, b.)...

One way is to label the pre-existing vesicles, and then follow the destiny of the label in the vesicle size distribution. The label that has been used to this aim is ferritin, which has been entrapped into vesicles. Ferritin is an iron-storage protein in plants and mammals, and consists of a hollow protein shell of c. 12 nm containing... 

Figure 10.11 The use of ferritin as a label for the mechanism of growth of vesicles (adapted from Berclaz et al, 2001a b). Schematic representation of the possible vesicle formation and transformation processes when oleate, and oleic acid, are added to pre-formed vesicles which have been labelled, (a) The situation if only de novo vesicle formation occurs, (b) Growth in size of the pre-formed and labeled vesicles which may lead to division, either yielding vesicles that all contain marker molecules (case i, a statistical redistribution of the ferritin molecules) or also yielding vesicles that do not contain markers (case ii). Compare all this with Figure 10.9.

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