Use of Liposomes to Model Aggregation and Fusion Phenomena

Vesicle aggregation by the antibody was studied by turbidimetry and freeze-fracture electron microscopy of samples frozen throughout the course of the aggregation. Rapid freezing was achieved with a double propane-jet apparatus. The advantage in using liposomes in studying aggregation and fusion phenomena stems from the possibility of controlling and manipulating their compositions and sizes. In addition, a variety of substances can be encapsulated in vesicles or incorporated in their membranes, which forms the basis for fusion assays based on aqueous contents or membrane mixing. The experimental problem is to determine the state of aggregation directly by counting particles or indirectly from certain spectroscopic procedures. Estimates were calculated from Smoluchowski-type kinetic equations, extended to include dissociation reactions. An extension of the analytic solution for the monomer-dimer system yielded a closed form expression for t in the general case. The analysis of kinetics of the overall fusion process56 indicated a dramatic increase in the rate constant of dissociation in this temperature range.