쿠싱증후군 환자에서 당 대사 이상 정도에 따른 인슐린 감수성과 인슐린 저항성의 변화

정인경,김성훈,정재훈,민용기,이명식,이문규,유형준,안규정,노정현,김동준,김광원 대한내분비학회 2003 Endocrinology and metabolism Vol.18 No.4

연구배경 당질 코르티코이드는 당 대사에 매우 중요한 호르몬으로 내인성 당질 코르티코이드 과다상태인 쿠싱증후군에서는 말초조직에서 인슐린 저항이 증가하고 이를 보상하고자 인슐린 분비의 증가로 고인슐린혈증이 동반된다고 보고되고 있다. 하지만 생체 내에서와 달리 시험관내에서는 췌도세포에 당질 코르티코이드를 장시간 처리하면, 인슐린 분비 및 생합성이직접적으로 억제됨이 확인된 바 있어 쿠싱증후군 환자에서 당뇨병의 원인으로는 아마도 말초조직에서 증가된 인슐린 저항성 뿐 아니라 이를 충분히 보상하지 못하는 췌장에서의 인슐린 분비 저하가 같이 동반되어있지 않을까 하는 가설을 세우게 되었고, 아직까지 당질코르티코이드가 당대사 이상을 일으키는 기전에 대해 쿠싱증후군을 당대사 정도에 따라 인슐린 감수성과 분비능을 분석한 연구는 없었기에 이를 알아보고자 하였다. 방법: 삼성서울병원에서 쿠싱증후군으로 진단 받은 환자 15명을 대상으로 하였다. 이에 대한 대조군으로는 쿠싱증후군 환자와 같은 성별 그리고 체질량지수를 갖은 15명의 건강한 성인을 대상으로 비교 하였다 쿠싱증후군 환자를 대상으로 경구당부하 검사를 통해 당대사 정도를 정상군, 내당능장애군, 그리고 당뇨병군으로 나눈 후 정맥 당부하 검사를 시행하여 각군의 인슐린 저항성과 인슐린 분비능의 지표를 비교하고, 수술 후 쿠싱증후군이 완치된 상태에서 수술 전후의 당대사 지표의 변화를 조사하였다. 결과: 1) 쿠싱증후군 환자 중 정상인은 20%, 내당능 장애는 27%, 그리고 당뇨병은 53%였다. 체질량지수, 나이, 그리고 발병 기간은 세 군간에 의미 있는 차이가 없었으나, 24시간 소변검사의 코르티솔 농도는 당뇨병군에서 의미있게 높았다. 2) 정맥당부하 검사 결과, 인슐린 감수성 지표인 Sl는쿠싱증추린」서 1.58±0.10[×10^(-4)(min^(-1)(μU/mL)^(-1)]로 정상 대조군의 3.37±0.49[×10^(-4)(min^(-1)(μU/mL)^(-1)]에 비해 의미있게 낮았으나(P=0.024), 쿠싱증후군 환자 중 NGT, IGT, DM 군간에 서로 통계적인 차이는 없었다. 3) SG는 정상 대조군과 쿠싱증후군 환자간에는 의미있는 차이가 없었고, 쿠싱 증후군에 있어서 당대사가 악화될수록 감소하는 경향을 보였으나 의미있는 차이는 없었다. 4) 인슐린 분비능의 지표인 AIRg는 정상인에 비해 전체 쿠싱증후군 환자의 경우 증가하는 경향을 보였으나 의미있는 차이는 없었다. 하지만 쿠싱증후군 환자중에서 당대사 상태에 따라 NGT군은 1299 (1297∼1310)(mu/g/min ×10^(-2))로 정상 대조군(368.9±98.6[mu/g/min ×10^(-2)]) 보다도 의미있게 높았고, DM군{202.2 (91.1~371.4) [mu/g/min ×10^(-2)}은 NGT군에 비해 의미있게 낮았다(P=0.0031). 5) 15명중 현재 완치 상태에 있는 6명에 대해 수술전과 후로 비교하였다. 수술 전 당대사 상태가 1명은정상, 1명은 내당능 장애, 그리고 4명은 당뇨병이었으나 수술 후 시행한 경구 당부하 검사상 모두 정상 당대사 상태를 보였다. 6) 수술 후 완치된 환자 6명에 있어 인슐린 감수성지표인 Sl는 수술전에 중앙값이 1.22[×10^(-4)(min^(-1)(μU/mL)^(-1)]로 대조군에 비해 의미있게 감고』어 있었으나(p.0.05), 수술후 10.95 [×10^(-4)(min^(-1)(μU/mL)^(-1)]로 정상 수준으로 회복되었고(P=0.0022), 인슐린 분비능을 나타내는 AIRg [mu/g/min ×10^(-2)] 값도 정상수준으로 회복되었다. 특히 인슐린 분비능의 회복양상은 혈당농도에 따라 판이하게 나타나서, 정상과 내당능장애 상태에 있던 2명은 수술전에 1201 [mu/g/min ×10^(-2)]로 증가되어 있던 AIRg 값이 수술 후 정상 수준으로 감소하였고, 수술 전에 당뇨병 상태에 있던 4명의 경우 245.9 [mu/g/min ×10^(-2)]로 인슐린 분비능이 감고il어 있었는데 이들은 수술 후 모두 정상 수준으로 증가되었다 (P=0.0286). 결론: 쿠싱증후군 환자에서 당대사 이상은 80%로 높은 유병률을 보였다. 모든 쿠싱증후군환자에서 인슐린 감수성은 정상인에 비해 저하되어 있어 말초조직의 인슐린 저항이 선행됨을 시사하며, 인슐린 분비능은 당대사의 정도에 따라 다르게 나타났는데, 정상 당대사군에서는 인슐린의 저항성을 극복할 만큼 정상 대조군보다 더 많은 양의 인슐린 분비를 하다가 고코르티솔혈증이 심할수록 인슐린 분비능의 감소로 당뇨병으로 진행됨을 확인할 수 있었고, 이런 인슐린 저항성과 인슐린 분비장애는 수술 후 다시 회복되는 가역적인변화를 보였다. Background: Glucocorticoid plays an important role in the control of carbohydrate metabolism. Patients with Cushing's syndrome have been reported to have an increased incidence of carbohydrate intolerance due to peripheral insulin resistance and hyperinsulinemia, although the exact incidence and nature of this disorder have remained unclear. Few results have been published about insulin resistance and insulin secretion according to the level of glucose concentration, or about the reversibility of such defects in patients with Cushing's syndrome. Methods: To assess the effect of glucocorticoid on the insulin sensitivity and insulin secretion in Cushing's syndrome, 15 patients with Cushing's syndrome were classified into 3 groups (normal glucose tolerance: NGT, impaired glucose tolerance: IGT, diabetes: DM) according to the degree of glucose tolerance based on the oral glucose tolerance test (OGTT). Insulin modified, frequently sampled, intravenous glucose tolerance test (FSIGT) was performed before and after curative surgery on these patients and on 15 healthy control subjects. Data were evaluated by non-parametric statistical analysis. Results: 1) Among the 15 patients with Cushing's syndrome, 3 (20%) were NGT, 4 (27%) IGT, and 8 (53%) DM, based on OGTT. Twenty-four hour urinary free cortisol (UFC) was significantly higher in the DM group. 2) Insulin sensitivity index (SI) of Cushing's syndrome was significantly lower than that of the control group p=0.0024), but was not significantly different among the three Cushing's syndrome groups of NGT, IGT and DM. 3) Glucose mediated glucose disposal (SG) (Ed- confirm this abbreviation; it does not seem to match the definition) of Cushing's syndrome was not significantly different from that of the control group. 4) Insulin secretion (AIRg) of Cushing's syndrome tended to be high, but it was not significantly different from that of control. However, according to the level of glucose concentration there was significant difference in AlRg among the three Cushing's syndrome groups p=0.0031); AIRg of DM was significantly lower than that of NGT. 5) After surgical treatment, parameters of insulin sensitivity and insulin secretion were normalized in 6 cured patients; 1 with NGT, 1 with IGT, and 4 with DM, preoperatively. Median SI of all 6 patients was significantly improved up to the normal range postoperatively p=0.0022). Median AIRg of these 6 patients was balanced around that of normal control postoperatively p=0.0286). Conclusion: Eighty percent of patients with Cushing's syndrome had abnormality of carbohydrate metabolism. Insulin sensitivity was significantly decreased in Cushing's syndrome. Insulin secretion was significantly higher only in the NGT and IGT groups of Cushing's syndrome. As the hypercortisolemia is exacerbated, insulin secretion is significantly decreased and causes DM, suggesting that glucocorticoid has a direct or indirect toxic effect on the pancreatic beta cell (J Kor SOC Endocrinol 18:392-403, 2003).

신장기능영상용 방사성의약품 Bz - MAG3 ( Benzoylmercaptoacetylglycylglycylglycine ) 의 키트화 및 체내분포

고창순(Chang Soon Koh),이명철(Myung Chul Lee),정준기(June Key Chung),이동수(Dong Soo Lee),김영주(Young Ju Kim),정재민(Jae Min Jeong),장영수(Young Soo Chang),조정혁(Jung Hyuk Cho) 대한핵의학회 1996 핵의학 분자영상 Vol.30 No.3

N/A The MAG3 is a tubular excreting radiopharmaceutical for renal image. We synthe-sized benzoyl MAG3 (Bz-MAG3) and made a kit for labeling with Tc-99m. We checked the labeling effeciency of Tc-99m labeled MAG3 and biodistribution. Labeling efficiency was checked by TLC- SG (acetonitrile/H2O=2/1). After injecting of 1 mCi of Tc-99M-MAG3 to ICR-mice, Tmax(min), T1/2(min) were obtained in the renogram. Sequencial images (30sec, 2min, 5min, 10min, 15min, 20min) of TC-99m-MAG3 were compared with those of commercial Tc-99m-DTPA (Du Pont Merck Pharmaceutical Co.) kit. 1) The Rf value of synthesized Tc-99m-MAG3 was 0.78 and labeling efficiency was 97.5±1.9% (n=10). 2) The dynamic images of the Tc-99m-MAG3 were better than those of the Tc-99m-DTPA. 3) The Tmax(min.) and T1/2(min.) of Tc-99m-MAG3 (n=10) were 1.5±0.5 (left), 1.4±0.4(right), and 4.3±1.4 (left), 4.8±2.0 (right), respectivel. The Tmax(min.) and T1/2(min.) of Tc-99m-DTPA (n=7) were 2.7±1.6 (left), 2.7±1.6 right), and 3.8±1.7 (left), 4.5±2.7 (right), respectively. The quaility of image and labeling efficiency of the synthesized Bz-MAG3 kit were excellent, that it was supposed to be used in routine clinical work.

Dose-linear pharmacokinetics of oleanolic acid after intravenous and oral administration in rats

Jeong, Dong Won,Kim, Young Hoon,Kim, Hui Hyun,Ji, Hye Young,Yoo, Sun Dong,Choi, Won Rack,Lee, Soo Min,Han, Chang-Kyun,Lee, Hye Suk WILEY PUBLISHERS 2007 BIOPHARMACEUTICS AND DRUG DISPOSITION Vol.28 No.2

<P>The pharmacokinetics of oleanolic acid was evaluated in vitro and in vivo. From Caco-2 cell permeation studies, oleanolic acid was a low permeability compound with no directional effects, suggesting a low in vivo absorption mediated by a passive diffusion. Oleanolic acid was metabolically unstable following incubation with rat liver microsomes in the presence of NADPH. After intravenous injection at doses of 0.5, 1 and 2 mg/kg doses, oleanolic acid showed dose-linear pharmacokinetics as evidenced by unaltered CL (28.6–33.0 ml/min/kg), V<SUB>ss</SUB> (437–583 ml/kg), dose-normalized AUC (16.0–17.9 µg min/ml based on 1 mg/kg) and t<SUB>1/2</SUB> (41.9–52.7 min). Following oral administration of oleanolic acid at doses of 10, 25 and 50 mg/kg, T<SUB>max</SUB>, t<SUB>1/2</SUB>, dose-normalized C<SUB>max</SUB> (66–74 ng/ml based on 25 mg/kg) and dose-normalized AUC (5.4–5.9 µg min/ml based on 25 mg/kg) were comparable between 25 and 50 mg/kg dose, but the plasma concentrations at 10 mg/kg dose were not measurable as they were below the limit of quantitation (2 ng/ml). The absolute oral bioavailability was 0.7% for oral doses of 25 and 50 mg/kg. The extent of urinary excretion was minimal for both i.v. and oral doses. The very low oral bioavailability of oleanolic acid could be due to a poor absorption and extensive metabolic clearance. Copyright © 2007 John Wiley & Sons, Ltd.</P>

Effects of hydrogen plasma treatment on SnO2:F substrates for amorphous Si thin film solar cells

Min-Seung Choi,Young-Ju Lee,Jung-Dae Kwon,Yongsoo Jeong,Ju-Yun Park,강용철,Pung Keun Song,Dong-Ho Kim 한국물리학회 2013 Current Applied Physics Vol.13 No.8

We investigated the effects of hydrogen plasma treatment on the physical and electrical properties of fluorine-doped tin oxide (FTO) films used for amorphous silicon (a-Si) thin film solar cells. A slight increase in carrier concentration by the hydrogen doping effect was observed for the FTO film exposed to the hydrogen plasma for 5 min. For further exposure to the plasma, the chemical reduction became prominent and resulted in deterioration of the electrical and optical properties of the film. XPS analysis revealed that the chemical reduction of SnO2 to Sn metallic state occurs on the surface region. It was found that the defects formed by hydrogen plasma act as recombination centers at the interface between FTO electrode and p-layer of a-Si solar cells. This phenomenon resulted in the deterioration of the cell performance. The averaged conversion efficiency (6.82%) of the cells on pristine FTO hydrogen substrate was decreased to 5.81% for the cells on FTO treated for 5 min, which is mainly attributed to the decrease in short-circuit current density.

초기 자궁내막암 환자에서의 복강경유도하 질식 자궁절제술과 복식 자궁절제술에 대한 비교 연구

김민규 ( Min Kyu Kim ),최동석 ( Dong Seok Choi ),김우영 ( Woo Young Kim ),최철훈 ( Chel Hun Choi ),김태중 ( Tae Joong Kim ),이정원 ( Jeong Won Lee ),김병기 ( Byoung Gie Kim ),이제호 ( Je Ho Lee ),배덕수 ( Duk Soo Bae ) 대한산부인과학회 2006 Obstetrics & Gynecology Science Vol.49 No.12

목적: 초기 자궁내막암의 수술적치료 시 복강경유도하 질식 자궁절제술 및 골반림프절절제술군과 복식수술군의 수술결과 및 재발율에 대해 비교하고자하였다. 연구 방법: 2003년 3월부터 2005년 5월까지 초기 자궁내막암 환자를 인구학적 특성이 같은 63명을 선택하여 복강경유도하 질식 자궁절제술 및 골반림프절절제술군 26명, 복식수술군 37명으로 나누어 수술 전후 혈색소 차이, 평균수술시간, 취득한 골반림프절갯수, 평균재원일수, 추가치료율, 재발률을 비교하였다. 결과: 복강경유도하 질식 자궁절제술 및 골반림프절절제술을 시행한 군과 복식수술을 시행한 군과의 비교에서 수술 전후 혈색소 차이, 평균수술시간, 취득한 골반림프절 갯수, 평균재원일수, 재발률에 통계적으로 유의한 차이가 없었다. 결론: 초기 자궁내막암의 수술 시 복강경유도하 질식자궁절제술 및 골반림프절절제술 방법이 복식방법에 비해 수술결과 및 재발률에 통계적으로 유의한 차이가 없으며 그 대체 수술법으로 많은 활용이 기대되었다. Objective: To compare laparoscopic surgery with conventional abdominal surgery in patients with early stage endometrial cancer. Methods: A retrospective review of 63 patients with early stage endometrial cancer managed between March 2003 and May 2005. Two groups were defined whether they had been treated by laparoscopy (case group: n=26) or by laparotomy (control group: n=37). We compared age, body mass index (BMI), hemoglobin change, operation time, number of pelvic lymph nodes, hospital stay, case with adjuvant treatment and recurrence between two groups. Results: There was no statistical difference in characteristics (age, BMI, nulliparity, previous abdominal surgery, FIGO stage, histologic grade). between case and control group. In addition, there was no statistical difference in operation data and outcomes between two groups. Hemoglobin changes were 1.1 g/dL (case group) vs 1.7 g/dL (control group) (p=0.072). Operation time was 131 min vs. 115 min. The numbers of lymph nodes obtained were 8.7 vs 7.7 (right) 9.2 vs. 7.6 (left). Hospital stays were 8.4 vs. 9.2 days. Adjuvant treatment cases were 7 vs. 15. Recurrent case was one in each group. Two patients initially evaluated by laparoscopy were converted to laparotomy due to bleeding and adhesion. Conclusion: Laparoscopic surgery for treatment of early endometrial cancer is a safe and effective alternative to laparotomy . However, long-term survival and risk of recurrence have yet to be determined.

The Effect of pH and Various Cations on the GTP Hydrolysis of Rice Heterotrimeric G-protein α Subunit Expressed in Escherichia Coli

Seo, Hak-Soo,Jeong, Jin-Yong,Nahm, Min-Yeop,Kim, Sam-Woong,Lee, Sang-Yeol,Bahk, Jeong-Dong Korean Society for Biochemistry and Molecular Biol 2003 Journal of biochemistry and molecular biology Vol.36 No.2

Previously, we reported the biochemical properties of RGA1 that is expressed in Escherichia coli (Seo et al., 1997). The activities of RGA1 that hydrolyzes and binds guanine nucleotide were dependent on the $MgCl_2$ concentration. The steady state rate constant ($k_{cat}$) for GTP hydrolysis of RGA1 at 2 mM $MgCl_2$ was $0.0075{\pm}0.0001\;min^{-1}$. Here, we examined the effects of pH and cations on the GTPase activity. The optimum pH at 2 mM $MgCl_2$ was approximately 6.0; whereas, the pH at 2 mM $NH_4Cl$ was approximately 4.0. The result from the cation dependence on the GTPase (guanosine 5'-triphosphatase) activity of RGA1 under the same condition showed that the GTP hydrolysis rate ($k_{cat}=0.0353\;min^{-1}$) under the condition of 2mM $NH_4Cl$ at pH 4.0 was the highest. It corresponded to about 3.24-fold of the $k_{cat}$ value of $0.0109\;min^{-1}$ in the presence of 2 mM $MgCl_2$ at pH 6.0.

G-CSF로 체내 증폭된 골수를 이용한 동종 조혈모세포이식

이종욱,김정아,민창기,김희제,엄현석,박수정,서정곤,김동욱,홍영선,민우성,김춘추,김동집 대한조혈모세포이식학회 1998 대한조혈모세포이식학회지 Vol.3 No.2

연구배경: 이식시 주입되는 골수세포수는 생착 속도 및 생존율과 밀접한 관계가 있으나, 임상적으로 환자의 체중이 공여자에 비해 지나치게 많을 때 단위 체중당 환자에게 주입되는 세포의 양이 적어 문제가 될 수 있다. 방법: 저자들은 가톨릭 조혈모세포이식 센터에서 동종 골수이식을 시행한 환자들 중 환자의 체중이 공여자에 비해 10kg이상 많은 경우 골수 채취 전에 공여자에게 3일간 피하로 G-CSF(10ug/kg/day)를 투여하여 골수를 체내(in vivo) 증폭시킨 후 골수이식을 시행한 25예의 환자를 대상으로 고식적인 방법으로 골수이식을 시행한 위험인자가 일치되는 대조군과 비교하여 이식된 세포수, 혈구의 회복속도 및 이식편대 숙주반응(GVHD)의 발생율, 그리고 생존율 등을 비교 분석하였다. 결과: 단기간의 G-CSF 투여로 증폭된 골수의 총 유핵세포수, 단핵구수는 대조군에 비해 3-5배, CD34 + 세포수는 6배 증폭되었으며, 두 군간에 세포의 면역표현형(CD4, CD5, CD7, CD8, CD20)의 차이는 없었다. 중성 백혈구 수가 0.5×10^(9)/L 이상 회복되는 시기는 두 군간의 차이가 없었으나(15.5일 vs 16일; p=0.131), 혈소판 수가 30×10^(9)/L 이상으로 회복되는 시기는 G-CSF 투여군에서 의의있게 단축되었다(20일 vs 26일; p=0.013). 두 군간 급성 및 만성 GVHD의 발생률과 정도의 차이는 없었으며, 이식 후 재발 및 생존율의 차이도 없었다. 결론: 이식전 공여자에게 단기간 G-CSF를 주사하여 생체내에서 골수 조혈모세포를 증폭시킨 후 이식하는 방법은 공여자와 환자의 심각한 체중 차이로 인해 단위체중당 이식되는 조혈모세포양이 부족한 환자들에게 안전하고 유용한 방법일 뿐만 아니라 GVHD의 증가 없이 빠른 혈구회복을 기대할 수 있는 이식기법이라고 생각한다. 향후 증폭된 골수 조혈모세포의 특성 연구 및 이의 효용성을 확인하기 위한 전향적인 연구가 필요하리라고 생각된다. Background: Sufficient stem cell doses are necessary to overcome engraftment failure in allogeneic bone marrow transplantation(BMT). Cell doses harvested may depend on body weight (BW) difference between donor and recipient. In practice, it is important to achieve large number of stem cells from donor who were lower BW than that of recipient. Methods: We have tried to inject G-CSF(10ug/kg/day) subcutaneously for 3 days to the allogeneic donor with lower BW than recipient before harvest to increase BM inoculum. BM was infused into patients without any manipulation on day 5. A total 25 patients were enrolled; 12 AML, 6 ALL, 5 SAA and 2 CML(expansion group). We compared the expansion group with 25 historical control patients, matched for diagnosis and clinical characteristics, who underwent unprimed BMT. Results: Recipient BW is not different between the expansion and control group. However, allogeneic donors in the control group weigh heavier than those in the expansion group. The yield of TNC, MNC, and CD34^(+) cells from G-CSFprimed BM was significantly higher than that from unprimed BM. There was no difference in immunophenotyping analysis(CD4, CD5, CD7, CD8, CD20) between two groups. The median time reaching to absolute neutrophil count more than 0.5×10^(9)/L was not different(15.5 vs 16 days: p=0.131), but time to platelet recovery more than 30×10^(9)/L was significantly shorter for the patients who received G-CSF-primed BM (20 vs 26 days: p=0.013). There was no difference in the incidence of acute and chronic GVHD, relapse rate and overall survival between the two groups with a median follow-up of 13 months. Conclusion: These data suggest that the short-term administration of G-CSF to an allogeneic donor prior to BM harvest seems to be a feasible method to achieve an adequate number of cell doses for patients who weigh higher than donors. Randomized, prospective study is needed to evaluate the efficacy of allogeneic BMT using in vivo expansion of BM by G-CSF.

허혈 유사 조건이 심방근의 활동전위 특성에 미치는 영향

김재하,주정민,조용범,신동호,안병희,주신배,김상형 대한순환기학회 1999 Korean Circulation Journal Vol.29 No.11

A study of ^99mTc-sestamibi labeling condition using radio-chromatography

Moon, Sung-Hyun,Lee, Yun-Sang,Lee, Dong Soo,Chung, June-Key,Jeong, Jae Min Korean Society of Radiopharmaceuticals and Molecul 2017 Journal of radiopharmaceuticals and molecular prob Vol.3 No.1

Tc-99m labeled sestamibi ($^{99m}Tc$-MIBI) is one of most widely used radiopharmaceuticals for myocardial SPECT imaging. Radiolabeling of $^{99m}Tc$-MIBI is recommended by heating in $100^{\circ}C$ water bath for 15 min. However, the water bath might be a source of contamination. Thus, if radiolabeling of $^{99m}Tc$-sestamibi can be performed at room temperature, then it would be more convenient to use in clinical application. In this study, we performed the radiolabeling of $^{99m}Tc$-MIBI in different temperature conditions or using different instruments to find out the efficient labeling condition. We studied the $^{99m}Tc$-MIBI labeling at room temperature or $100^{\circ}C$ heating block, and checked the labelling yields every 1 min for 10 min using radio-TLC with 2 different eluents-saline and acetone. From the experiment, we confirmed that the $^{99m}Tc$-MIBI can be labeled over 90% yield but not completed at room temperature. However, the $^{99m}Tc$-MIBI labeling was completed when it was performed in the $100^{\circ}C$ heating block. Finally, we proved that heating is essential for complete $^{99m}Tc$-MIBI labelling, furthermore using heating block is also possible instead of water bath.

The Effect of pH and Various Cations on the GTP Hydrolysis of Rice Heterotrimeric G-protein α Subunit Expressed in Escherichia Coli

( Hak Soo Seo ),( Jin Yong Jeong ),( Min Yeop Nahm ),( Sam Woong Kim ),( Sang Yeol Lee ),( Jeong Dong Bahk ) 생화학분자생물학회 2003 BMB Reports Vol.36 No.2

Previously, we reported the biochemical properties of RGAl that is expressed in Escherichia coli(Seo et al., 1997). The activities of RGAl that hydrolyzes and binds guanine nucleotide were dependent on the MgCl_(2) concentration. The steady state rate constant (k_(cat)) for GTP hydrolysis of RGAl at 2 mM MgCl_(2) was 0.0075±0.0001 min^(-1). Here, we examined the effects of pH and cations on the GTPase activity. The optimum pH at 2mM MgCl_(2) was approximately 6.0; whereas, the pH at 2 mM NH_(4)Cl was approximately 4.0. The result from the cation dependence on the GTPase (guanosine 5`-triphosphatase) activity of RGAl under the same condition showed that the GTP hydrolysis rate (k_(cat)=0.0353 min^(-1)) under the condition of 2mM NH_(4)Cl at pH 4.0 was the highest. It corresponded to about 3.24-fold of the k_(cat) value of 0.0109 min^(-1) in the presence of 2mM MgCl_(2) at pH 6.0.