Evaluation of the purity of commercially available phenylalanine ammonia lyase and variables affecting its encapsulation efficiency in cellulose nitrate microcapsules

Oral administration of phenylalanine ammonia lyase (PAL) encapsulated in microcapsules is potentially a novel approach for treatment of phenylketonuria. However, low activity of encapsulated PAL precludes its clinical application. Incomplete entrapment of PAL into cellulose nitrate microcapsules partially accounts for poor activity of encapsulated PAL. One objective of this research was to evaluate manufacturing variables affecting encapsulation efficiency of PAL into cellulose nitrate microcapsules. It was determined that order of addition of hemoglobin solution in preparation of water-in-oil emulsion affected encapsulation efficiency. Additionally, use of freshly prepared cellulose nitrate solution and adjustment of Tris buffer pH at 4°C seemed to increase PAL encapsulation efficiency. Maximum encapsulation efficiency of almost 70% was observed in these studies. The second purpose of this research was to evaluate purity of commercially available PAL as a prelude to radiolabelling. Using polyacrylamide gel electrophoresis and mass spectrometry it was observed that commercially available PAL contains contaminants.