Preparation, activity and structure of cross-linked enzyme aggregates (CLEAs) with nanoparticle

Cross-linked enzyme aggregates (CLEAs) have emerged as an interesting biocatalyst design for enzyme immobilization. However, the commercialization of CLEAs is often hampered by their shortcomings, such as poor-controlled particle size, low activity and sticky characteristic. In order to overcome these drawbacks, five nanoparticles (NPs) (nano-TiO₂, nano-MgO, nano-Ni, nano-Cu and nano-Fe₃O₄) were used to improve CLEAs activity and structure in this study. Results showed that moderate dosage of nano-TiO₂ addition increased CLEAs activity, and the most increment was 15.2% relative to CLEAs without NPs. This was possibly due to more channels and smaller size particle of CLEAs after nano-TiO₂ addition. Moreover, nano-TiO₂ addition not only decreased fluorescence intensity but also caused the red shift in tryptophan (Trp) and tyrosine (Typ) residues. Nano-TiO₂ addition decreased K_m and increased V_max of CLEAs. These changes were benefit to the activity and structure of CLEAs. However, addition of other four NPs (nano-MgO, nano-Ni, nano-Cu and nano-Fe₃O₄) did not increase CLEAs activity and even decrease CLEAs activity due to less amorphous cavities and larger or discrete particle size than CLEAs without NPs. In addition, FT-IR results showed that NPs addition increases the content of regular structure of CLEAs, and causes a partial transformation of β-turn into β-sheet. This study showed that it was potential to improve CLEAs performance by nano-TiO₂ addition.