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Aggregation of ligand-modified liposomes by specific interactions with proteins. II: Biotinylated liposomes and antibiotin antibody |
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Nancy J. Lynch, Peter K. Kilpatrick, Ruben G. Carbonell |
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Department of Chemical Engineering, |
Correspondence to Ruben G. Carbonell, Department of Chemical Engineering, North Carolina State University, Box 7905, Raleigh, North Carolina 27695
Funded by:
National Science Foundation
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liposomes; biotin; aggregation kinetics |
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The aggregation of biotinylated phospholipid vesicles (liposomes) cross-linked by antibiotin IgG was studied experimentally and theoretically. The liposomes were either low density liposomes that contained 0.4 mol% biotinylated phospholipid (@100 exposed biotin molecules per liposome), or high density liposomes that contained 2.7 mol% biotinylated phospholipid (@1000 exposed biotin molecules per liposome). The solution turbidity and mean particle size measured by quasi-elastic light scattering (QLS) were monitored throughout the aggregation. Three different lots of antibiotin antibodies, each with different association constants and binding heterogeneities, were used. The antibody binding characteristics affected the aggregation rates. The aggregation kinetics were analyzed using a model based on the Smoluchowski theory of aggregation, fractal concepts of aggregate microstructure, and Rayleigh and Mie light scattering theory. The experimental conditions of liposome concentration, protein concentration, and ligand density under which aggregation occurred correlated well with calculated sticking probabilities based on isotherms describing the adsorption of antibiotin antibody to the liposomes. These results are compared with prior observations made when avidin was used as the cross-linking protein. |