Use of a Reversed-PhaseEvaporationVesicleFormulationfor a

Complement-mediated release of enzyme molecules from reversed-phaseevaporationvesiclesserves as the basisof the sensitivehomogeneousimmunoassayreported here.We found it necessary to co-entrap the substrate glucose 6-phosphate with the bacterial enzyme glucose-6-phosphate dehydrogenase (EC 1.1.1.49) to protect enzyme activity during liposome preparation. Enzyme can be released spe-cificallyfrom these liposomes by incubationwith antibody and complement. The enzyme is not merely available to substrate but is actually physicallyfree of the liposomes. Inhibition of this complement-mediated lysis by theophylline is the basis for the homogeneous liposome immunoassay described.The assay resultsvary linearlywith theophylline concentrationsin plasma in the clinicallyrelevantrange, and serum components do not interfere. The reagents in th