Preparation and properties of cross-linked enzyme aggregates of phenylalanine ammonia lyase in the aminated macroporous silica gel

The cross- linked enzyme aggregates of phenylalanine ammonia lyase ( PAL) in aminated ( activited) macroporous silica gel ( MSG ( SG) - PAL- CLEAs) were prepared by the cross- linked enzyme aggregates technology.The conditions for the preparation of aminated macroporous silica gel and MSG ( SG) - PAL- CLEAs were optimized, respectively.Moreover, stability of free PAL, PAL-CLEAs, MSG-PAL-CLEAs and SG-PAL-CLEAs was evaluated and compared.The optimized conditions for preparing amino- modified macroporous silica gel ( MSG) were as follows: the ratio of APTES and macroporous silica gel, 2∶1 ( v/w) ; temperature, 110℃; time, 10h.The content of amino-group was 480μmol /g under optimized conditions.The optimum conditions for preparing MSG- PAL-CLEAs could be summarized as: 0.05g MSG and 1mL free PAL sulotion ( pH8.8) were incubated at room temperature for 2.5h, and then precipitated with 80%- saturation ammonia sulfate for 1h followed by crosslinking with 1% glutaraldehyde for 1h.The optimized condition for preparing SG- PAL- CLEAs was similar with the MSG- PAL- CLEAs except that the saturation of ammonia sulfate was 40% and the terminal concentration of glutaraldehyde was 1.5%.The results showed that the activity recoveries of MSG- PAL- CLEAs and SG- PALCLEAs were approximately 45%.Moreover, compared with PAL- CLEAs, the reusability and storage stability of MSG- PAL- CLEAs and SG- PAL- CLEAs were improved.MSG- PAL- CLEAs retained about 79% of it initial activities after four transforming batches, but PAL- CLEAs retained about 49% after two transforming batches.At25℃, PAL-CLEAs retained about 26% of it initial activities after 29d, MSG-PAL-CLEAs retained about 50%.