• Bulletin of the Korean Chemical Society
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• v.22 no.2
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• pp.154-158
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• 2001

The steps for the generation of very thin GaN films on ultrathin AlN/6H-SiC surface by alternating a pulsative supply (APS) of trimethyl gallium and NH3 gases have been examined by ASED-MO calculations. We postulate that the gallium cul ster was formed with the evaporation of CH4 gases via the decomposition of trimethyl gallium (TMG), dimethyl gallium (DMG), and monomethyl galluim (MMG). During the injection of NH3 gas into the reactor, the atomic hydrogens were produced from the thermal decomposition of NH3 molecule. These hydrogen gases activated the Ga-C bond cleavage. An energetically stable GaN nucleation site was formed via nitrogen incorporation into the layer of gallium cluster. The nitrogen atoms produced from the thermal degradation of NH3 were expected to incorporate into the edge of the gallium cluster since the galliums bind weakly to each other (0.19 eV). The structure was stabilized by 2.08 eV, as an adsorbed N atom incorporated into a tetrahedral site of the Ga cluster. This suggests that the adhesion of the initial layer can be reinforced by the incorporation of nitrogen atom through the formation of large grain boundary GaN crystals at the early stage of GaN film growth.

• Journal of Photoscience
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• v.9 no.2
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• pp.150-153
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• 2002

Solar UV light is a well-known carcinogen. UVA radiation is probably carcinogenic to humans. In addition, recent investigations point to the importance of UVA irradiation in the photoaging. We investigated the mechanism of sequence- specific DNA damage using $\^$32/P-Iabeled DNA fragments in relation to carcinogenesis and aging. Furthermore, we investigated whether UVA accelerates the telomere shortening in human WI-38 fibroblasts. The exposure of double- stranded DNA fragments to 365 nm light in the presence of endogenous sensitizers produced sequence-specific cleavage at the 5' site of 5'-GG-3' and 5'-GGG-3' sequences. In addition, HPLC analysis revealed that sensitizers plus 365 nm light increased the 8-oxodG content of double-stranded DNA. We discuss the mechanisms of guanine-specific DNA damagecaused by excited photosensitizers in relation to carcinogenesis and aging.

• Journal of Korean Society of Water and Wastewater
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• v.9 no.2
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• pp.127-135
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• 1995

The purpose of this study was to more fully evaluate the potential for chlorophenol degradation in anaerobic sludge. The pH effects on the ring cleavage of phenol and dechlorination of monochlorophenol isomers and dichlorophenl isomers. This study results are as follows ; Each of the monochlorophenol isomers were degraded in anaerobic sludge. The relatives rates were 2-Chlorophenol > 3-Chlorophenol > 4-Chlorophenol. Biodegradation results for the dichlorophenol isomers in anaerobic sludge are such as 2,3-dichlorophenol and 2,5-dichlorophenol was reductively dechlorinated to 3-chlorophenol, 2,4-dichlorophenol to 4-chlorophenol, 2,6-dichlorophenol to 2-chlorophenol. The two dichlorophenol isomers which did not contain an ortho Cl substituent 3,4-dichlorophenol and 3,5-dichlorophenol were persistent during the 6-week incubation. The rate of dechlorination was enhanced by the presence of a Cl group ortho, rather than para, to the site of dechlorination.

• Bulletin of the Korean Chemical Society
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• v.26 no.12
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• pp.1911-1920
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• 2005

Effective artificial metalloproteases have been designed by using cross-linked polystyrene as the backbone. Artificial active sites comprising Cu(II) complexes as the catalytic site and other metal centers or organic functionalities as binding sites were synthesized. The activity of Cu(II) centers for peptide hydrolysis was greatly enhanced on attachment to polystyrene. By placing binding sites in proximity to the catalytic centers, the ability to hydrolyze a variety of protein substrates at selected cleavage sites was improved. Thus far, the most advanced immobile artificial proteases have been obtained by attaching the aldehyde group in proximity to the Cu(II) complex of cyclen.

• Journal of the Korean Society of Food Science and Nutrition
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• v.20 no.1
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• pp.35-39
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• 1991

Properties of a protease purified from Neungee[Sarcodon aspratus(Berk, ) S. Ito] have been investigated. The enzyme displays a glycosylated serine protease. The enzyme is able to hydrolyze alanine glycine methionine glutamine and cysteine of N-CBZ and N-t-BOC-L-amino acid derivatibes relatively strongly but splits valine proline and isoleucine derivatives with low affinity which means the enzyme has the broad substrate spectrum toward the amino acids. Interestingly the enzyme was inhibited by bromelain inhibitor. That is the active site environ-ment of the enzyme is believed to be similar to that of bromelain However peptide mapping studies show that the two enzymes have distinct different cleavage sites.

• Korean Journal of Microbiology
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• v.24 no.2
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• pp.86-90
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• 1986

The DNA methylated by Hpa II methylase was not cleaved by Sma, I, Ava I and Nae I endonucleases. This experimental data could be interpreted as strong evidences that Sma I, Ava I and Nae I methylases which yet to be isolated would methylate on the inmost cytosine nucleotide within their hexameric recognition sequences. The facts that Sma I, Ava I and Nae I endonucleases can not cleave the DNA methylated by Hpa II methylase are the valuable informations for protecting DNAs upon cleavage reactions by Sma I, Ava I and NAe I endonucleases especially for cDNA insertion experiments into vector DNAs using Sma I, Ava I and Nae I oligonucleotide linkers. In the case of Xma I endonuclease, partially cleaved DNA fragments were observed although the reaction rate was greatly decreased. This result implies that the methylation site of Xma I methylase which yet to be isolated would not be the same as that of Hpa II methylase in Xma I sequence.

• Journal of Microbiology and Biotechnology
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• v.14 no.6
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• pp.1280-1285
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• 2004

Retron is a prokaryotic genetic element, producing a short single-stranded DNA covalently linked to RNA (msDNA-RNA) by a reverse transcriptase (RT). In retron EC83, msDNA is further processed at between the 4th and the $5^{th}$ nucleotides, leaving a 79 nucleotide-long single-stranded DNA as a final product. To investigate this site-specific cleavage in msDNA synthesis, we purified the RT protein of retron EC83. Initially, RT ORF was cloned under the tac promoter, but the expression was very poor largely because of poor translation. In order to facilitate translation, the nucleotide sequence for the first nine amino acids was randomized with synonymous codons. This change of downstream sequence of translational initiation codon greatly affected the efficiency of translation. We could isolate clones which greatly increased RT production, and their sequences were compared to those of the low producers. The overproduced protein was purified and was shown to have RT activity.

• Microbiology and Biotechnology Letters
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• v.18 no.1
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• pp.94-97
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• 1990

The restriction cleavage map of multi-copy recombinant plasmid, pJY502 (5.5 kb), carrying the thiostrepton resistance gene (tsr) was determined. Comparison of the restriction pattern with that of Streptomyces plasmids previously demonstrated that pJY502 was novel. The plasmid pJY502 had a broad host range in Streptomyces and contained single BgtII site for cloning purpose. Transformation frequency of pJY502 was $2.2 \times 10^5$ in S. lividans. E. coti-Streptomyces bifunctional plasmid, pJY504, was also constructed.

• Journal of Microbiology and Biotechnology
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• v.5 no.5
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• pp.269-273
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• 1995

A thermotolerable restriction endonuclease. Svil, found in Streptomyces violochromogenes D2-5 was purified. For the purification, streptomycin sulfate and ammonium sulfate precipitation was used. Ph osphocellulose P-ll, DEAE-Cellulose and Sephacryl-S200 HR colum chromatography were also performed. The purified enzyme was found to be homogeneous and the molecular weight of the enzyme estimated by polyacrylamide gel electrophoresis containing 0.1$%$ SDS was about 32, 000 daltons. The recognition sequence and cleavage site of the enzyme were determined to be $5^1$-$TT\downarrow CGAA$-$3^1$ which is the same sequence as that of Asull. Unlike Asull, however, the Svil shows high thermal stability.

• Proceedings of the Korean Biophysical Society Conference
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• 1996.07a
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• pp.4-4
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• 1996

$\alpha$$_1$-arantitrypsin, a member of the serpin (serine protease inhibitor) family, undergoes a large structural rearrangement upon the cleavage and insertion of the reactive site loop. This conformational change is driven by the metastability of the native serpin structures and has an important role in the regulation of the inhibitory-serpin function. (omitted)