Liposomes compartmentalized reactions

As a final remark, it is clear that the choice of liposome preparation method depends on the experiment s aim. Since we are dealing with compartmentalized reactions, it is often convenient to reach the maximum entrapment efhciency, in order to have filled vesicles. We will see in next section what are the general strategies to entrap chemicals inside vesicles, and how to feed them with an externally added reactant Another important issue, discussed below, is the chemical compatibility between the hpids, the preparation method, and the (bio)chemicals used in the experiments. 

Figure 17.4 Two general strategies to carry out a compartmentalized reaction X + Y = Z. (A) Liposomes are formed in the presence of X, which is entrapped then the free (unentrapped) X is removed, and later the second reactant Y is added. (B) Liposomes are formed in the presence of reactants X and Y, unentrapped material is removed (or a not-permeant inhibitor is added). The reaction is then started by physical means (e.g., temperature, light). X and Y may represent a single chemical specie, or a collection of reactants. When two or more reactants are simultaneously entrapped, the issue of composition of individual liposome may become relevant for interpretation of data. In panel B, for example, not all liposomes contain both X and Y (this condition may become critical for a large number of reactants)...

In this section we will discuss briefly some theoretical aspects related to the design and realization of compartmentalized reactions, mainly derived from our experience with biochemical systans. As a general premise, we remade that although an ever inoeasing number of published work on this subject (mono- or multi-enzymatic reactions inside liposomes, fatty add vesicles, polymersomes, as well as w/o or w/o/w compartments ) a full understanding of the physico-chemical details of compartmentalized reactions has not been reached. A related field, which has a longer tradition, i.e. that one of enzymes in reverse micelles has revealed interesting compartmentation-dependent mechanisms. ... 

The importance of compartmentalized reactions is constantly growing and evolving. After about 20 years from the first reports on enzymes inside liposomes, current research deals also with the assembly of semi-synthetic cells. 

Entrapment of nucleic acids has also been achieved in liposomes, originally for gene transfer therapy, and later on for the study of the influence of compart-mentalization on biochemical reactions involving DNA and RNA. Entrapped DNA refers to genetic material which is compartmentalized in the internal waterpool of... 

Once established the chemical stability of the urea-urease reaction in the presence of lipids and of the fluorescent probe, the next step towards a successful oscillating system was the encapsulation of the enzyme into POPC liposomes through the droplet transfer method. This innovative method first takes advantage of the facile compartmentalization of water-soluble solutes (enzyme in this case) in water-in-oil (w/o) droplets, and then convert the solute-filled w/o droplets into vesicles that can be dispersed in an acidic solution of urea. 

---