Cross-linkedα-amylase aggregates on Fe3O4 magnetic nanoparticles modified with polydopamine/polyethyleneimine for efficient hydrolysis of starch

In this workα-amylase was immobilized on magnetic Fe3O4 nanoparticles with polyethylenimine(PEI)/polydopamine(PDA)coating or 3-aminopropyl triethoxysilane(APTES)for the first time via adsorption–precipitation–cross-linking.Compared with the freeα-amylase,the resultant magnetic cross-linkedα-amylase aggregates(PEI/PDA-M-CLEAs and N-M-CLEAs)exhibited excellent thermal and storage stability as well as pH stability.After storage at 25°C for 60 days,freeα-amylase only retained 60%of its initial activity,while PEI/PDA-M-CLEAs and N-M-CLEAs retained 80%and 78%of their initial activities,respectively.Furthermore,N-M-CLEAs and PEI/PDA-M-CLEAs showed good reusability.After 6 repeated uses,PEI/PDA-M-CLEAs and N-M-CLEAs still maintained 65%and 62%of their initial activities,respectively.Especially,PEI/PDA-M-CLEAs and N-M-CLEAs exhibited higher starch hydrolysis efficiency than freeα-amylase.The maximum dextrose equivalent(DE)values of starch hydrolysis by PEI/PDA-M-CLEAs and N-M-CLEAs reached 29.24%and 28.79%within 90 min,respectively.However,the maximum DE values of starch hydrolysis by the freeα-amylase was only 27.89%even in 150 min.The magnetic cross-linkedα-amylase aggregates could be introduced as effective biocatalyst for industrial applications in production of maltose syrups.

Assembly of IMPDH2-Based,CTPS-Based,and Mixed Rod/Ring Structures Is Dependent on Cell Type and Conditions of Induction

Inhibition of guanosine triphosphate（GTP） and cytidine triphosphate（CTP） biosynthetic pathways induces cells to assemble rod/ring（RR） structures,also named cytoophidia,which consist of the enzymes cytidine triphosphate synthase（CTPS） and inosine-50-monophosphate dehydrogenase 2（IMPDH2）.We aim to explore the interaction of CTPS and IMPDH2 in the generation of RR structures.He La and COS-7 cells were cultured in normal conditions or in the presence of 6-diazo-5-oxo-L-norleucine（DON）,ribavirin,or mycophenolic acid（MPA）.Over 90% of DON-treated cells presented RR structures.In He La cells,35% of the RR structures were positive for IMPDH2 alone,26% were CTPS alone,and 31% were IMPDH2/CTPS mixed,while in COS-7 cells,42% of RR were IMPDH2 alone,41% were CTPS alone,and 10% were IMPDH2/CTPS mixed.Ribavirin and MPA treatments induced only IMPDH2-based RR.Cells were also transfected with an N-terminal hemagglutinin（NHA）-tagged CTPS1 construct.Over 95% of NHA-CTPS1 transfected cells with DON treatment presented IMPDH2-based RR and almost 100% presented CTPS1-based RR;when treated with ribavirin,over 94% of transfected cells presented IMPDH2-based RR and 37% presented CTPS1-based RR,whereas 2% of untreated transfected cells presented IMPDH2-based RR and 28% presented CTPS1-based RR.These results may help in understanding the relationship between CTP and GTP biosynthetic pathways,especially concerning the formation of filamentous RR structures.