The entrapment of α-chymotrypsin (α-CT) within 70-140 nm liposomes formed from POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) leads to an unexpected and remarkable increase in the thermal stability of the enzyme. This finding is based on the observation that heating aqueous suspensions of α-CT-containing POPC liposomes to 80 °C for 30 minutes resulted in partial enzyme inactivation, whereas the same treatment of aqueous solutions of free α-CT inactivated the enzyme completely. The stabilizing effect of enzyme confinement in the attoliter volumes of the liposomes was found to increase with decreasing numbers of α-CT molecules per liposome. Single-enzyme confinement was particularly effective, as intermolecular interactions between heat-denatured α-CT molecules (causing irreversible inactivation) are not possible.
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