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Jin-Mok Lee(이진목),Kwang-Jin Park(박광진),Min-Ju Kim(김민주),In-Jeong Ko(고인정),Jeong-Il Oh(오정일) 한국생명과학회 2010 생명과학회지 Vol.20 No.6
DevSR two-component system은 Mycobacterium smegmatis의 redox sensing에 관련된 주요한 regulatory system이다. DevSR system은 DevS histidine kinase와 DevR response regulator로 구성되어 있다. 저산소 조건에서 DevS histidine kinase는 활성화되어 DevR response regulator를 인산화 시키고, 인산화된 DevR response regulator는 DevR regulon의 transcriptional activator로 작용한다. DevS의 kinase activity는 DevS의 N-terminal에 위치한 GAF domain에 존재하는 heme의 ligand-binding state에 의해 결정된다. 본 연구에서는 C-terminal kinase domain의 redox-responsive cysteine (C547)이 DevS kinase activity의 redox-dependent control과 연관이 있음을 밝혔다. 산소가 존재할 때, C547 residue 사이의 disulfide bond의 형성은 DevS kinase activity를 불활성화 시킨다. β-mercaptoethanol과 dithiothreitol과 같은 환원제를 이용하여 산화된 DevS를 환원시켰을 때, DevS kinase activity가 복원된 것이 관찰되었다. 또한, C547을 alanine으로 치환했을 때, M. smegmatis의 DevS의 sensory 기능을 부분적으로 손상되는 것이 complementation 실험을 통해 in vivo 상에서 증명되었다. The DevSR two-component system is a major regulatory system involved in redox sensing in Mycobacterium smegmatis. The DevSR system consists of the DevS histidine kinase and its cognate DevR response regulator. When exposed to hypoxic conditions, the DevS histidine kinase is activated to phosphorylate the DevR response regulator, leading to the transcriptional activation of the DevR regulation. The ligand-binding state of the heme embedded in the N-terminal GAF domain of DevS determines the kinase activity of DevS. In this study, we demonstrated that the redox-responsive cysteine (C547) in the C-terminal kinase domain is involved in the redox-dependent control of DevS kinase activity. The formation of an intersubunit disulfide bond between the C547 residues in the presence of O₂ led to inactivation of DevS kinase activity. The reduction of the oxidized DevS with reductants such as β-mercaptoethanol and dithiothreitol resulted in the restoration of DevS kinase activity. It was demonstrated in vivo by complementation test that the substitution of C547 to alanine partially impaired the sensory function of DevS in M. smegmatis.
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Guo Xian,Jeong mok Oh(오정목),Junghoon Lee(이정훈),Sangmyung Cho(조상명),Jongtak Yeom(엄종탁),Yoonsuk Choi(최윤석),Namhyun Kang(강남현) 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.5
Wire arc additive manufacturing (WAAM) is a process that combines an electric arc as a heat source and a wire as feedstock to build a component layer by layer. In arc welding, heat input is an important characteristic because it influences the cooling rate, which could affect the mechanical properties and microstructure of the deposition part. We investigated the effect of heat input on the microstructure and mechanical property of the additive layer manufactured for Ti64 alloys. High-heat input (H; 1 kJ/mm) produced a columnar grain exhibiting a large anisotropic property of tensile strength. Low-heat input (L; 0.5 kJ/mm) transformed the columnar grains to the equiaxed ones, and its reason was associated with the solidification cooling rates accelerated. However, the H specimens exhibited a larger tensile strength and hardness than the L specimens, which can be explained by volume fraction of the hardened phase (α’ martensite and secondary α). The microstructure in H and L specimens were further identified by SEM-EDX and TEM. The thermal history in the WAAM deposits was also simulated using finite element method. At the certain temperature gradient, the faster cooling rates produced the more fraction of the equiaxed grains. Furthermore, the H specimens exhibited more thermal cycles calculated to verify the condition that can produce more α’ martensite and secondary α. Therefore, the L specimen changed the grain structure to equiaxed one and reduced the anisotropy of tensile strength significantly.
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Guo Xian,Jeong mok Oh(오정목),Junghoon Lee(이정훈),Sangmyung Cho(조상명),Jongtak Yeom(엄종탁),Yoonsuk Choi(최윤석),Namhyun Kang(강남현) 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.5
Wire arc additive manufacturing (WAAM) is a process that combines an electric arc as a heat source and a wire as feedstock to build a component layer by layer. In arc welding, heat input is an important characteristic because it influences the cooling rate, which could affect the mechanical properties and microstructure of the deposition part. We investigated the effect of heat input on the microstructure and mechanical property of the additive layer manufactured for Ti64 alloys. High-heat input (H; 1 kJ/mm) produced a columnar grain exhibiting a large anisotropic property of tensile strength. Low-heat input (L; 0.5 kJ/mm) transformed the columnar grains to the equiaxed ones, and its reason was associated with the solidification cooling rates accelerated. However, the H specimens exhibited a larger tensile strength and hardness than the L specimens, which can be explained by volume fraction of the hardened phase (α’ martensite and secondary α). The microstructure in H and L specimens were further identified by SEM-EDX and TEM. The thermal history in the WAAM deposits was also simulated using finite element method. At the certain temperature gradient, the faster cooling rates produced the more fraction of the equiaxed grains. Furthermore, the H specimens exhibited more thermal cycles calculated to verify the condition that can produce more α’ martensite and secondary α. Therefore, the L specimen changed the grain structure to equiaxed one and reduced the anisotropy of tensile strength significantly.
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Guo Xian,Jeong mok Oh(오정목),Junghoon Lee(이정훈),Sangmyung Cho(조상명),Jongtak Yeom(엄종탁),Yoonsuk Choi(최윤석),Namhyun Kang(강남현) 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.5
Wire arc additive manufacturing (WAAM) is a process that combines an electric arc as a heat source and a wire as feedstock to build a component layer by layer. In arc welding, heat input is an important characteristic because it influences the cooling rate, which could affect the mechanical properties and microstructure of the deposition part. We investigated the effect of heat input on the microstructure and mechanical property of the additive layer manufactured for Ti64 alloys. High-heat input (H; 1 kJ/mm) produced a columnar grain exhibiting a large anisotropic property of tensile strength. Low-heat input (L; 0.5 kJ/mm) transformed the columnar grains to the equiaxed ones, and its reason was associated with the solidification cooling rates accelerated. However, the H specimens exhibited a larger tensile strength and hardness than the L specimens, which can be explained by volume fraction of the hardened phase (α’ martensite and secondary α). The microstructure in H and L specimens were further identified by SEM-EDX and TEM. The thermal history in the WAAM deposits was also simulated using finite element method. At the certain temperature gradient, the faster cooling rates produced the more fraction of the equiaxed grains. Furthermore, the H specimens exhibited more thermal cycles calculated to verify the condition that can produce more α’ martensite and secondary α. Therefore, the L specimen changed the grain structure to equiaxed one and reduced the anisotropy of tensile strength significantly.
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고인정,김용진,이진목,신선주,오정일,Ko, In-Jeong,Kim, Yong-Jin,Lee, Jin-Mok,Shin, Sun-Joo,Oh, Jeong-Il Korean Society of Life Science 2006 생명과학회지 Vol.16 No.4
본 연구에서는 lacZ transcriptional fusion plasmid를 이용하여 광합성 세균인 Rhodobacter sphaeroides에서의 7가지 광합성유전자 (puf, puc, puhA, bchC, bchE, bchF, bchI) 발현의 경향과 조절을 조사하였다. R. sphaeroides에서 puhA와 bchI를 제외한 모든 광합성유전자들이 호기적 조건과 비교했을 때 혐기적 조건에서 더욱 강하게 발현되었다. puhA 유전자는 bchFNBHLM-RSP0290과 operon을 형성하며, bchI 유전자는 crtA와 operon을 이루는 것으로 나타났다. 광합성 조건에서 자란 R. sphaeroides의 puf, puc, bchCXYZ operon의 발현은 빛의 세기에 비례하는 반면, bchFNBHLM(RSP0290 puhA) operon의 발현은 빛의 세기에 반비례 하였다. bchEJG의 발현은 $10\;W/m^2$의 빛이 조사된 광합성 조건에서 제일 낮았으며, $100\;W/m^2$의 빛의 광합성 조건에서 가장 높았다. R. sphaeroides의 산소인지와 빛 인지에 관련된 세 가지 주요 조절기작에 의한 광합성유전자 조절은 다음과 같다. puf와 bchC는 PpsR repressor와 PrrBA two-component system에 의해 조절된다. 그리고 puc operon은 PpsR, FnrL, PrrBA system에 의해 조절된다. bchE의 발현은 FnrL과 PrrBA system에 의해 조절되는 반면, bchF는 오로지 PpsR에 의해서만 조절된다. PpsR repressor는 강한 세기의 빛 조건에서 bchf 발현억제의 원인이 되며, FnrL은 그 자체가 산소를 인지하는 기능 이외에도 세포질의 산화/환원 상태의 인지에 관련될 것으로 보인다. Here we examined the expression patterns and regulation of seven photosynthesis (PS) genes (puf, puc, puhA, bchC, bchE, bchF, and bchI) in the anoxygenic photosynthetic bacterium, Rhodobacter sphaeroides, based on lacZ reporter gene assay. Expression of the tested PS genes, except puhA and bchI, were strongly induced in R. sphaeroides grown under anaerobic conditions relative to that under aerobic conditions. The puhA and bchI genes appear to form the operons together with bchFNBHLM-RSP0290 and crtA, respectively. Expression of the puf, puc, and bchCXYZ operons in R. sphaeroides grown photosynthetically was proportional to the incident light intensity, whereas that of bchFNBHLM(RSP0290-puhA) was inversely related to light intensity. Expression of bchEJG was lowest under medium-light photosynthetic conditions $(10\;W/m^2)$ and highest under high light conditions $(100\;W/m^2)$. The regulation of PS genes by the three major regulatory systems involved in oxygen- and light-sensing in R. sphaeroides is as following: puf and bchC are regulated by both the PpsR repressor and the PrrBA two-component system. The puc operon is under control of PpsR, FnrL, and PrrBA system. Expression of bchE is controlled by FnrL and PrrBA two-component system, whereas bchF is regulated exclusively by PpsR. It was demonstrated that the PpsR repressor is responsible for high-light repression of bchF and that FnrL might be involved in perceiving the cellular redox state in addition to sensing $O_2$ itself.
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