Ee Taek Hwang

Immobilization and stabilization of subtilisin Carlsberg in magnetically-separable mesoporous silica for transesterification in an organic solvent

Subtilisin Carlsberg (SC) was immobilized and stabilized on magnetically-separable mesoporous silica (Mag-MSU-F) in the form of nanoscale enzyme reactors (NERs) based on the ship-in-a-bottle mechanism. Stabilized NERs of SC (NER-SC) were freeze-dried and successfully used for the transesterification of N-acetyl-L-phenylalanine ethyl ester with n-propanol in isooctane. Magnetic separation of Mag-MSU-F facilitated the repeated usages of stable NER-SC. This is the first demonstration for the use of stable and magnetically-separable NERs in an organic solvent, which has the potential for environmentally-friendly synthesis using enzymes in organic solvents.

New functional amorphous calcium phosphate nanocomposites by enzyme-assisted biomineralization.

In the present study, we report on enzyme-assisted formation of biomineralized amorphous calcium phosphate nanocomposites (ACP-NCs). About 100-200 nm sizes of the spherical porous enzyme-assisted ACP-NCs were successfully synthesized via double reverse microemulsion, but no ACP-NCs formed without the enzyme. It is believed that the enzyme was used as an organic template or additive that could regulate the biomineralization process. The enzyme-assisted ACP-NCs were well characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, dynamic light scattering, and Brunauer-Emmett-Teller (BET) criteria. The BET surface area, total pore volume, pore size from adsorption, and pore size from desorption of the ACP-NCs were 163 m(2) g(-1) or 0.37 cm(3) g(-1), 8.87 nm, and 7.48 nm, respectively. The enzyme-assisted ACP-NCs retained about 43% of the catalytic activity of free carboxyl esterase. Furthermore, they preserved their bioactivity even after the 10th reuse and were stable over 10 days even under a stringent shaking conditions. The reported method paves the way for novel biomineralization via enzyme molecules to form functional enzymes containing nanocomposites.

Carbonic anhydrase assisted calcium carbonate crystalline composites as a biocatalyst

In the present study, we report on the carbonic anhydrase (CA)-assisted formation of biomineralized calcium carbonate crystalline composites (CCCCs). Ellipsoidal CCCCs, such as calcite polymorphism, in a micro-size range catalyzed by CA were successfully synthesized with polyethylene glycol and magnetic nanoparticles in the constant CO2 pressure controlled chamber, for the first time. CA-assisted CCCCs characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and dynamic light scattering, showed their crystalline phase with mesoporous property according to Fourier transform infrared and Brunauer–Emmett–Teller area. These CCCCs retained about 43% of free CA esterase activity. Furthermore, the magnet-based separation was also successful for the reuse of the CCCCs. As a result, the CCCCs produced preserved their catalytic activity even after its ten repeated usages, and were stable for more than 50 days under room temperature. The reported method paves the way for novel biomineralization via CA for the formation of functional CA containing nanocomposites and biocatalyst technology applications.

Prediction and classification of the modes of genotoxic actions using bacterial biosensors specific for DNA damages

We report on a novel approach to predict the mode of genotoxic action of chemicals using a series of DNA damage specific bioluminescent bacteria. For this, a group of seven different DNA damage sensing recombinant bioluminescent strains were employed. Each of these strains was tested against model DNA damaging agents, such as mitomycin C (MMC), 1-methyl-1-nitroso-N-methylguanidine (MNNG), nalidixic acid (Nal) and 4-nitroquinoline N-oxide (4-NQO). These biosensors were grouped based on their responses to a specific mode of genotoxic action, such as (a) DNA damage cascade response (biosensor with nrdA-, dinI- and sbmC-lux), (b) SOS response or DNA repair (strains carrying recA-, recN- and sulA-lux), and (c) DNA damage potentially by alkylation (biosensor with alkA-lux). The differential response patterns and its strength of these strains to various model genotoxicants allowed classifying the chemicals potential genotoxic mode. Therefore, it is possible to elucidate and classify the mode of genotoxic impacts of an unknown sample and that together they may be utilized in the pre-screening steps of new drugs, newly synthesized chemicals, food and environmental contaminants.

Aptamers-on-nanofiber as a novel hybrid capturing moiety

In this study, we present a new bio-inspired hybrid capturing moiety, aptamers on a polymeric polystyrene–poly(styrene-co-maleic anhydride) nanofiber, for the purification of target protein. These novel hybrid composites were successfully fabricated by immobilizing aptamers on nanofibers synthesized by electrospinning. The advantageous characteristics of nanofibers, such as a very large surface to volume ratio and flexible modification of the surface, contributed to the greatly improved surface coverage of aptamers, resulting in the highly increased capturing capacity of the target proteins. As a result, this increased capturing capacity led to 85% of recovery yield in the protein purification. In addition to easy preparation and cost effectiveness of this system, these novel aptamers-on-nanofiber composites showed good stability with no conspicuous reduction in the purification efficiency, even after repeated use for seven months.

Highly-stable magnetically-separable organic-inorganic hybrid microspheres for enzyme entrapment

Organic-inorganic hybrid microspheres for a magnetically separable and highly stable enzyme system were successfully fabricated. After enzymes were entrapped, these hybrid microspheres were found to be highly stable for more than 120 days with about 75% of the initial activity preserved, and were successfully reused more than 10 times repeatedly. Furthermore, magnet-based separation was also found to be successful for the repeated usage.

CO2 bioconversion using carbonic anhydrase (CA): effects of PEG rigidity on the structure of bio-mineralized crystal composites.

The combined effect of both carbonic anhydrase (CA) and the rigidity of polyethylene glycol (PEG) were found to assist the bio-mineralized crystallization behavior of CO2 differentially. In this study, different forms of magnetically responsive calcium carbonate (CaCO3) crystal composites were successfully formed from gaseous CO2 by using the different forms of polyethylene glycols (PEGs) in a constant CO2 pressure controlled chamber. Polygonal particles were produced with more rigid polymer chains (branched PEG), whereas less rigid polymer chains (PEG) induced the formation of ellipsoidal particles. However, no morphological changes occurred without the presence of CA.