Hyon Soo Han

Gene Cloning, Sequencing, and Expression of an Esterase from Acinetobacter lwoffii I6C-1

The esterase-encoding gene, estA, was cloned from Acinetobacter lwoffii I6C-1 genomic DNA into Escherichia coli BL21(DE3) with plasmid vector pET-22b (pEM1). pEM1 has a 4.4-kb EcoRI insert that contained the complete estA gene. A 2.4-kb AvaI-SphI DNA fragment was subcloned (pEM3) and sequenced. estA gene encodes a protein of 366 amino acids (40,687 Da) with a pI of 9.17. The EstA signal peptide was 31 amino acids long, and the mature esterase sequence is 335 amino acids long (37.5 kDa). The conserved catalytic serine residue of EstA is in position 210. The EstA sequence was similar to that of the carboxylesterase from Acinetobacter calcoaceticus (75% identity, 85% similarity), Archaeoglobus fulgidus (37% identity, 59% similarity), and Mycobacterium tuberculosis (35% identity, 51% similarity). These enzymes contained the conserved motif G-X1-S-X2-G carrying the active-site serine of hydrolytic enzyme. The EstA activity in A. lwoffii I6C-1 remains constant throughout the stationary phase, and the activity in E. coil BL21 (DE3) with pEM1 was similar to A. lwoffii I6C-1.

Potential use of P-32 ophthalmic applicator: Monte Carlo simulations for design and dosimetry.

Postoperative beta-irradiation after pterygium excision has been considered a valuable therapeutic procedure to reduce the recurrence rate. Recently, it was reported that beta-irradiation also substantially reduced the risk of surgical failure after glaucoma surgery. Pure beta-irradiation using a 90Sr/Y applicator has been almost exclusively used for this purpose. As an alternative to 90Sr/Y beta-irradiation, we propose treatment with betas of a 32P source. While 32P has a lower maximum energy (1.71 MeV) than 90Sr/Y (2.27 MeV), it has an average energy comparable to that of 90Sr/Y. Furthermore, it can be produced easily in a nuclear reactor by neutron activation and is considered a less hazardous material. Monte Carlo simulations for the dosimetry of proposed 32P applicators were performed using the MCNP5 code. The structure and dimension of the 32P applicators were based on those of the 90Sr/Y applicators currently available, while medical plastic encapsulation and liquid source were chosen to enhance beta-dose to the surface of the conjunctiva. The 32P applicator showed that the surface dose distribution (up to 0.75 mm depth) is very similar to that of 90Sr/Y. However, beyond 0.75 mm depth, the 32P doses decrease with depths more rapidly than 90Sr/Y doses. In order to achieve the same surface dose rate, the required 32P activity is about three times that for a 90Sr/Y applicator. We conclude that the proposed 32P applicator can deliver therapeutic doses to the target lesion while sparing the lens better than the 90Sr/Y applicator. The 32P activity required to deliver therapeutic doses can be produced in a 30 MW reactor available at the Korea Atomic Energy Research Institute.

A radioimmunoassay method for detection of DNA based on chemical immobilization of anti-DNA antibody

High selectivity provided by biomolecules such as antibodies and enzymes has been exploited during the last two decades for development of biosensors. Of particular importance are efficient immobilization methods for biomolecules in order to preserve their biological activities. In this study, we have evaluated immobilization strategies for an anti-DNA antibody on a self-assembled monolayer of ω-functionalized thiols. The antibody was immobilized via peptide bond formation between the primary amines in the antibody and the carboxyl groups on the self-assembled monolayer. The peptide bond coupling was achieved by activating COOH groups on the surface through N-Hydroxysuccimide (NHS)-ester formation, followed by acylation of NH2 group in the antibody. DNA binding activity of the immobilized antibody was examined by counting β emission from 35S-labeled DNA.

Dosimetry of a new P‐32 ophthalmic applicator

PURPOSE The potential of P-32 ophthalmic applicator irradiation after pterygium excision has been demonstrated as an alternative to Sr∕Y-90 irradiation. This study aimed to provide the clinical dosimetry for this new applicator. METHODS The prototype of a cylindrical P-32 applicator was fabricated according to the Monte Carlo (MC)-based design study. At a nominal activity of 6 mCi (0.22 GBq), the absorbed dose rate at the front surface (i.e., reference dose rate) was measured by using an extrapolation ionization chamber (EC). The radiochromic film (RCF) was also used to measure the reference dose, axial depth dose distributions and transaxial dose profiles at various depths in water. RESULTS The reference dose rate was 3.89 ± 0.14 cGy∕s for EC and 3.84 ± 0.25 cGy∕s for RCF. The depth dose rate was reduced approximately by an order of magnitude for every 2 mm depth in water. Measured depth doses in depths of 0.5-2.5 mm agreed with Monte Carlo data within ±3%. Due to nonuniform absorption of P-32 into an absorbent disk, the dose profiles were not symmetric and decreased more rapidly toward the periphery than those predicted by the MC. The authors confirmed no leakage of P-32 activities and negligible exposure rate around the hand grip of the applicator. CONCLUSIONS The P-32 applicator can deliver therapeutic doses to the surface of the conjunctiva, while sparing the lens better than Sr∕Y-90 applicators. The doses at any points from the P-32 applicator could be calculated by using the measured dosimetry data. They also confirmed no leakage of the source, reliable integrity of the applicator, and negligible exposure level around the hand grip of the applicator. However, due to a possibility of nonuniform distributions of P-32 in an absorbent disk, measuring dose profiles as well as the reference dose rate for every new applicator would be recommended.

Dosimetry of a New P-32 Ophthalmic Applicator

Purpose: A 90Sr/Y applicator has been used as a β-source for postoperative irradiation after pterygium excision. As an alternative to 90Sr/Y irradiation, we proposed treatments with 32P. This study aims to provide the dosimetry for this new applicator. Method and Materials: A 32P ophthalmic applicator, of which the design and materials were optimally designed by Monte Carlo simulations, was fabricated by the Korea Atomic Energy Research Institute. The absorbed dose at the front surface of the cylindrical 32P applicator was measured by using an extrapolation ionization chamber. Radiochromic film (RCF) was used to measure depth dose distributions and dose profiles at various depths. A micro-MOSFET detector was used for depth dose measurements. Results: The absorbed dose rates to the reference point (i.e., at the centre on the front surface of 32P applicator) were 0.238 ± 0.012 cGy/s for an extrapolation ionization chamber, 0.280 ± 0.001 cGy/s for RCF, and 0.257 ± 0.020 cGy/s for MOSFET. The axial depth dose rate was reduced into approximately 1/10 as 32P betas penetrate every 2 mm depth. Measured data in depths of 1 mm to 3.5 mm agreed with Monte Carlo data. Due to non-uniform absorption of 32P into an absorbent disk, the dose at the centre of trans-axial plane was 2%–4% less than the peak dose around the periphery. We confirmed no leakage of 32P activities and negligible exposure rate around the hand grip of the applicator. Conclusions: The 32P applicator can deliver uniform therapeutic doses to the surface of the conjunctiva, while sparing the lens better than 90Sr/Y applicators. The doses at any points from the 32P applicator can be calculated by using these measured data sets. The safety of 32P applicator was confirmed. However, prior to the clinical application of every new applicator, safety, dose uniformity, and absorbed dose rate at the reference point should be carefully evaluated by the method developed in this study.