This chapter discusses the enzyme entrapment in liposomes. The usefulness of liposomes as vehicles for the administration of enzymes and other therapeutic agents derives from the fact that, as lipid molecules undergo rearrangements prior to the formation of closed structures, there is unrestricted entry of solutes between the planes of polar head groups. In discussing enzyme entrapment, two aspects that are relevant to medical applications will be considered. These are (a) efficient entrapment procedures giving a low liposomal lipid-entrapped enzyme ratio, and (b) criteria for real entrapment as opposed to external binding onto the liposomal surface. Entrapment of an enzyme or of any other solute in liposomes is a passive process: as liposomes form, they embrace and trap volumes of water containing the solutes. In is therefore apparent that the extent to which solutes can be entrapped is proportional to the volume of the aqueous phase within liposomes, which in turn is related to the charge of the inner or outer surface of the lipid bilayer and to the ionic strength of the medium used for the formation of liposomes. The preparation of enzyme-containing liposomes is exceedingly simple. The appropriate lipids are dissolved in an organic solvent, which is subsequently eliminated under reduced pressure, leaving a thin lipid layer on the walls of the flask. This is dispersed with the enzyme solution and liposomes containing the enzyme form spontaneously. Prior to their separation from nonentrapped enzyme, liposomes can be reduced in size by sonication down to mono lamellar structures. © 1976, Elsevier Inc. All rights reserved.
Gregoriadis, G., Leathwood, P. D., & Ryman, B. E. (1971). Enzyme entrapment in liposomes. FEBS Letters, 14(2), 95–99. https://doi.org/10.1016/0014-5793(71)80109-6