Strategies to maximize the encapsulation efficiency of phenylalanine ammonia lyase in microcapsules

The activity of phenylalanine ammonia lyase (PAL) encapsulated in cellulose nitrate microcapsules is only 23% of the activity of PAL in Tris buffer. This lower activity is partially due to its incomplete encapsulation. The objective of the study was to maximize the encapsulation efficiency (EE) of PAL by optimizing different formulation parameters. PAL was purified using size exclusion chromatography and then radioiodinated using the Iodo-gen reaction. Use of 125I-PAL showed that PAL had an EE of 45% in cellulose nitrate microcapsules. Formulation parameters including concentration of polymer in solution, stirring speed and ratio of aqueous phase volume to organic phase volume were individually optimized to maximize the EE of PAL. The reformulated microcapsules showed an EE of PAL of 80%. The dramatic increase in EE was reflected in a marked (119%) increase in the activity of encapsulated PAL compared to its activity in the original microcapsules. Eighty two percent of the encapsulated PAL was physically present in the aqueous core while 18% was entrapped in the microcapsule membrane. Distribution of PAL activity in the microcapsule was in concordance with its physical distribution.