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1.  Noninvasive Markers for the Diagnosis of Nonalcoholic Fatty Liver Disease 
Endocrinology and Metabolism  2013;28(4):280-282.
PMCID: PMC3871044  PMID: 24396692
2.  Clinical Marker of Platelet Hyperreactivity in Diabetes Mellitus 
Diabetes & Metabolism Journal  2013;37(6):423-428.
Atherothrombotic complications are important causes of morbidity and mortality in diabetic patients. Diabetes has been considered to be a prothrombotic status. Several factors contribute to the prothrombotic condition, such as increasing coagulation, impaired fibrinolysis, endothelial dysfunction, and platelet hyperreactivity. Among the factors that contribute to the prothrombotic status in diabetes, altered platelet function plays a crucial role. Although understanding platelet function abnormalities in diabetes still remains as a challenge, more attention should be focused on platelet function for effective management and the prediction of atherothrombotic events in diabetic patients. This review will provide an overview on the current status of knowledge of platelet function abnormalities and clinical marker of platelet hyperreactivity in patients with diabetes.
PMCID: PMC3881326  PMID: 24404513
Blood platelets; Diabetes mellitus; Hyperreactivity; Marker
4.  How Can We Measure the Effects of Exercise in Daily Life? 
Korean Diabetes Journal  2010;34(1):21-22.
PMCID: PMC2879898  PMID: 20532016
6.  Hemoglobin A1c Is Positively Correlated with Framingham Risk Score in Older, Apparently Healthy Nondiabetic Korean Adults 
Endocrinology and Metabolism  2013;28(2):103-109.
Several studies have suggested that elevated levels of hemoglobin A1c (HbA1c) are associated with cardiovascular disease (CVD) in nondiabetic individuals. However, it is unclear whether HbA1c levels can serve as a simple screening marker for increased CVD risk in nondiabetic individuals. Our objective was to evaluate the relationship between HbA1c levels and CVD risk using the Framingham risk score (FRS) in older, apparently healthy nondiabetic Korean adults.
We retrospectively studied 2,879 Korean adults between the ages of 40 and 79 who underwent voluntary health check-ups at the Health Promotion Center of our hospital from July 2009 to June 2011. Subjects were subdivided based on their HbA1c levels into four groups: tertiles within the HbA1c normal tolerance range and a group for subjects with an increased risk for diabetes (IRD).
The mean FRS for the upper tertile (9.6±3.8) group was significantly higher than that of the middle tertile (8.4±4.0) and lower tertile (7.6±3.8) groups. In addition, FRS was highest in the IRD group (10.5±3.7). Multiple linear regression analysis demonstrated that HbA1c levels exhibited a significant positive correlation with FRS when adjusted for confounding variables in all subjects (β±standard error [SE], 0.018±0.002; R2, 0.131), women (β±SE, 0.023±0.003; R2, 0.170), and men (β±SE, 0.016±0.004; R2, 0.109).
HbA1c levels were positively correlated with FRS in older, apparently healthy nondiabetic Korean adults. We propose that HbA1c levels may reflect CVD risk in nondiabetic individuals.
PMCID: PMC3811715  PMID: 24396663
Hemoglobin A, glycosylated; Framingham risk score; Nondiabetic individuals
7.  Evaluation of Immunogenicity and Safety of the New Tetanus-Reduced Diphtheria (Td) Vaccines (GC1107) in Healthy Korean Adolescents: A Phase II, Double-Blind, Randomized, Multicenter Clinical Trial 
Journal of Korean Medical Science  2013;28(4):586-592.
This phase II clinical trial was conducted to compare the immunogenicity and safety of a newly developed tetanus-reduced diphtheria (Td) vaccine (GC1107-T5.0 and GC1107-T7.5) and control vaccine. This study was also performed to select the proper dose of tetanus toxoid in the new Td vaccines. Healthy adolescents aged between 11 and 12 yr participated in this study. A total of 130 subjects (44 GC1107-T5.0, 42 GC1107-T7.5 and 44 control vaccine) completed a single dose of vaccination. Blood samples were collected from the subjects before and 4 weeks after the vaccination. In this study, all subjects (100%) in both GC1107-T5.0 and GC1107-T7.5 groups showed seroprotective antibody levels (≥ 0.1 U/mL) against diphtheria or tetanus toxoids. After the vaccination, the geometric mean titer (GMT) against diphtheria was significantly higher in Group GC1107-T5.0 (6.53) and GC1107-T7.5 (6.11) than in the control group (3.96). The GMT against tetanus was 18.6 in Group GC1107-T5.0, 19.94 in GC1107-T7.5 and 19.01 in the control group after the vaccination. In this study, the rates of local adverse reactions were 67.3% and 59.1% in GC1107-T5.0 and GC1107-7.5, respectively. No significant differences in the number of adverse reactions, prevalence and degree of severity of the solicited and unsolicited adverse reactions were observed among the three groups. Thus, both newly developed Td vaccines appear to be safe and show good immunogenicity. GC1107-T5.0, which contains relatively small amounts of tetanus toxoid, has been selected for a phase III clinical trial.
PMCID: PMC3617313  PMID: 23579367
Tetanus-Reduced Diphtheria (Td) Vaccine; Immunogenicity; Safety
8.  Clinical Features of Symptomatic Meckel's Diverticulum in Children: Comparison of Scintigraphic and Non-scintigraphic Diagnosis 
Meckel's diverticulum (MD) has various clinical manifestations, and diagnosis or selectection of proper diagnostic tools is not easy. This study was conducted in order to assess the clinical differences of MD diagnosed by scintigraphic and non-scintigraphic methods and to find the proper diagnostic tools.
We conducted a retrospective review ofthe clinical, surgical, radiologic, and pathologic findings of 34 children with symptomatic MD, who were admitted to Gachon University Gil Medical Center, Inha University Hospital, and The Catholic University of Korea, Incheon St. Mary's Hospital between January 2000 and December 2012. The patients were evaluated according to scintigraphic (12 cases; group 1) and non-scintigraphic (22 cases; group 2) diagnosis.
The male to female ratio was 7.5 : 1. The most frequent chief complaint was lower gastrointestinal (GI) bleeding in group 1 and nonspecific abdominal pain in group 2, respectively. The most frequent pre-operative diagnosis was MD in both groups. Red blood cell (RBC) index was significantly lower in group 1. MD was located at 7 cm to 85 cm from the ileocecal valve. Four patients in group 1 had ectopic gastric tissues causing lower GI bleeding. The most frequent treatment modality was diverticulectomy in group 1 and ileal resection in group 2, respectively.
To diagnose MD might be delayed unless proper diagnostic tools are considered. It is important to understand indications of scintigraphic and non-scintigraphic methods according to clinical and hematologic features of MD. Scintigraphy would be weighed in patients with anemia as well as GI symptoms.
PMCID: PMC3746044  PMID: 24010105
Meckel's diverticulum; Scintigraphy; Meckel's scan; Diagnosis; Child; Radionuclide imaging
9.  miR-34 miRNAs provide a barrier for somatic cell reprogramming 
Nature cell biology  2011;13(11):1353-1360.
Somatic reprogramming induced by defined transcription factors is a low efficiency process that is enhanced by p53 deficiency 1-5. To date, p21 is the only p53 target shown to contribute to p53 repression of iPSC (induced pluripotent stem cell) generation 1, 3, suggesting additional p53 targets may regulate this process. Here, we demonstrated that mir-34 microRNAs (miRNAs), particularly miR-34a, exhibit p53-dependent induction during reprogramming. mir-34a deficiency in mice significantly increased reprogramming efficiency and kinetics, with miR-34a and p21 cooperatively regulating somatic reprogramming downstream of p53. Unlike p53 deficiency, which enhances reprogramming at the expense of iPSC pluripotency, genetic ablation of mir-34a promoted iPSC generation without compromising self-renewal and differentiation. Suppression of reprogramming by miR-34a was due, at least in part, to repression of pluripotency genes, including Nanog, Sox2 and Mycn (N-Myc). This post-transcriptional gene repression by miR-34a also regulated iPSC differentiation kinetics. miR-34b and c similarly repressed reprogramming; and all three mir-34 miRNAs acted cooperatively in this process. Taken together, our findings identified mir-34 miRNAs as novel p53 targets that play an essential role in restraining somatic reprogramming.
PMCID: PMC3541684  PMID: 22020437
10.  Ascorbic acid prevents loss of Dlk1-Dio3 imprinting and facilitates generation of all-iPS cell mice from terminally differentiated B cells 
Nature genetics  2012;44(4):398-S2.
The generation of induced pluripotent stem cells (iPSCs) often results in aberrant epigenetic silencing of the imprinted Dlk1-Dio3 gene cluster, which compromises the cells’ ability to generate entirely iPSC-derived adult mice (“all-iPSC mice”). Here, we show that reprogramming in the presence of ascorbic acid attenuates hypermethylation of Dlk1-Dio3 by enabling a chromatin configuration that interferes with binding of the de novo DNA methyltransferase Dnmt3a. This allowed us to generate all-iPSC mice from mature B cells, which have thus far failed to support the development of exclusively iPSC-derived postnatal animals. Our data demonstrate that transcription factor-mediated reprogramming can endow a defined, terminally differentiated cell type with a developmental potential equivalent to that of embryonic stem cells. More generally, these findings indicate that culture conditions during cellular reprogramming can strongly influence the epigenetic and biological properties of resultant iPSCs.
PMCID: PMC3538378  PMID: 22387999
11.  New Betulinic Acid Derivatives as Potent Proteasome Inhibitors 
In this study, 22 new betulinic acid (BA) derivatives were synthesized and tested for their inhibition of the chymotrypsin-like activity of 20S proteasome. From the SAR study, we concluded that the C-3 and C-30 positions are the pharmacophores for increasing the proteasome inhibition effects, and larger lipophilic or aromatic side chains are favored at these positions. Among the BA derivatives tested, compounds 13, 20, and 21 showed the best proteasome inhibition activity with IC50 values of 1.42, 1.56, and 1.80 µM, respectively, which are three- to four-fold more potent than the proteasome inhibition controls LLM-F and lactacystin.
PMCID: PMC3171619  PMID: 21856154
12.  Effectiveness of Nicardipine for Blood Pressure Control in Patients with Subarachnoid Hemorrhage 
The purpose of the study is to determine the effectiveness and safety of nicardipine infusion for controlling blood pressure in patients with subarachnoid hemorrhage (SAH).
We prospectively evaluated 52 patients with SAH and treated with nicardipine infusion for blood pressure control in a 29 months period. The mean blood pressure of pre-injection, bolus injection and continuous injection period were compared. This study evaluated the effectiveness of nicardipine for each Fisher grade, for different dose of continuous nicardipine infusion, and for the subgroups of systolic blood pressure.
The blood pressure measurement showed that the mean systolic blood pressure / diastolic blood pressure (SBP/DBP) in continuous injection period (120.9/63.0 mmHg) was significantly lower than pre-injection period (145.6/80.3 mmHg) and bolus injection period (134.2/71.3 mmHg), and these were statistically significant (p < 0.001). In each subgroups of Fisher grade and different dose, SBP/DBP also decreased after the use of nicardipine. These were statistically significant (p < 0.05), but there was no significant difference in effectiveness between subgroups (p > 0.05). Furthermore, controlling blood pressure was more effective when injecting higher dose of nicardipine in higher SBP group rather than injecting lower dose in lower SBP group, and it also was statistically significant (p < 0.05). During the infusion, hypotension and cardiogenic problems were transiently combined in five cases. However, patients recovered without any complications.
Nicardipine is an effective and safe agent for controlling acutely elevated blood pressure after SAH. A more systemic study with larger patients population will provide significant results and will bring solid evidence on effectiveness of nicardipine in SAH.
PMCID: PMC3471255  PMID: 23210033
Nicardipine; Hypertension; Subarachnoid hemorrhage; Aneurysm
13.  A rapid and scalable system for studying gene function in mice using conditional RNA interference 
Cell  2011;145(1):145-158.
RNA interference is a powerful tool for studying gene function, however, the reproducible generation of RNAi transgenic mice remains a significant limitation. By combining optimized fluorescence-coupled miR30-based shRNAs with high efficiency ES cell targeting, we developed a fast, scalable pipeline for the production of shRNA transgenic mice. Using this system, we generated eight tet-regulated shRNA transgenic lines targeting Firefly and Renilla luciferases, Oct4 and tumor suppressors p53, p16INK4a, p19ARF and APC and demonstrate potent gene silencing and GFP-tracked knockdown in a broad range of tissues in vivo. Further, using an shRNA targeting APC, we illustrate how this approach can identify predicted phenotypes and also unknown functions for a well-studied gene. In addition, through regulated gene silencing we validate APC/Wnt and p19ARF as potential therapeutic targets in T cell acute lymphoblastic leukemia/lymphoma and lung adenocarcinoma, respectively. This system provides a cost-effective and scalable platform for the production of RNAi transgenic mice targeting any mammalian gene.
PMCID: PMC3244080  PMID: 21458673
14.  Inhibitory Effects of Olmesartan on Catecholamine Secretion from the Perfused Rat Adrenal Medulla 
The present sutdy aimed to determine whether olmesartan, an angiotensin II (Ang II) type 1 (AT1) receptor blocker, can influence the CA release from the isolated perfused model of the rat adrenal medulla. Olmesartan (5~50 µM) perfused into an adrenal vein for 90 min produced dose- and time-dependent inhibition of the CA secretory responses evoked by ACh (5.32 mM), high K+ (56 mM, a direct membrane-depolarizer), DMPP (100 µM) and McN-A-343 (100 µM). Olmesartan did not affect basal CA secretion. Also, in adrenal glands loaded with olmesartan (15 µM), the CA secretory responses evoked by Bay-K-8644 (10 µM, an activator of voltage-dependent L-type Ca2+ channels), cyclopiazonic acid (10 µM, an inhibitor of cytoplasmic Ca2+ -ATPase), veratridine (100 µM, an activator of voltage-dependent Na+ channels), and Ang II (100 nM) were markedly inhibited. However, at high concentrations (150~300 µM), olmesartan rather enhanced the ACh-evoked CA secretion. Taken together, these results show that olmesartan at low concentrations inhibits the CA secretion evoked by cholinergic stimulation (both nicotininc and muscarinic receptors) as well as by direct membrane depolarization from the rat adrenal medulla, but at high concentrations it rather potentiates the ACh-evoked CA secretion. It seems that olmesartan has a dual action, acting as both agonist and antagonist at nicotinic receptors of the isolated perfused rat adrenal medulla, which might be dependent on the concentration. It is also thought that this inhibitory effect of olmesartan may be mediated by blocking the influx of both Na+ and Ca2+ into the rat adrenomedullary chromaffin cells as well as by inhibiting the Ca2+ release from the cytoplasmic calcium store, which is thought to be relevant to the AT1 receptor blockade, in addition to its enhancement on the CA secreton.
PMCID: PMC2933441  PMID: 20827339
Olmesartan; Catecholamine secretion; Adrenal medulla; AT1 receptor blockade
15.  Fermentative Production of Thymidine by a Metabolically Engineered Escherichia coli Strain▿  
Thymidine is an important precursor in the production of various antiviral drugs, including azidothymidine for the treatment of AIDS. Since thymidine-containing nucleotides are synthesized only by the de novo pathway during DNA synthesis, it is not easy to produce a large amount of thymidine biologically. In order to develop a host strain to produce thymidine, thymidine phosphorylase, thymidine kinase, and uridine phosphorylase genes were deleted from an Escherichia coli BL21 strain to develop BLdtu. Since the genes coding for the enzymes related to the nucleotide salvage pathway were disrupted, BLdtu was unable to utilize thymidine or thymine, and thymidine degradation activity was completely abrogated. We additionally expressed T4 thymidylate synthase, T4 nucleotide diphosphate reductase, bacteriophage PBS2 TMP phosphohydrolase, E. coli dCTP deaminase, and E. coli uridine kinase in the BLdtu strain to develop a thymidine-producing strain (BLdtu24). BLdtu24 produced 649.3 mg liter−1 of thymidine in a 7-liter batch fermenter for 24 h, and neither thymine nor uridine was detected. However, the dUTP/dTTP ratio was increased in BLdtu24, which could lead to increased double-strand breakages and eventually to cell deaths during fermentation. To enhance thymidine production and to prevent cell deaths during fermentation, we disrupted a gene (encoding uracil-DNA N-glycosylase) involved in DNA excision repair to suppress the consumption of dTTP and developed BLdtug24. Compared with the thymidine production in BLdtu24, the thymidine production in BLdtug24 was increased by ∼1.2-fold (740.3 mg liter−1). Here, we show that a thymidine-producing strain with a relatively high yield can be developed using a metabolic engineering approach.
PMCID: PMC2675214  PMID: 19251902
16.  Isomaltose Production by Modification of the Fructose-Binding Site on the Basis of the Predicted Structure of Sucrose Isomerase from “Protaminobacter rubrum”▿ † 
Applied and Environmental Microbiology  2008;74(16):5183-5194.
“Protaminobacter rubrum” sucrose isomerase (SI) catalyzes the isomerization of sucrose to isomaltulose and trehalulose. SI catalyzes the hydrolysis of the glycosidic bond with retention of the anomeric configuration via a mechanism that involves a covalent glycosyl enzyme intermediate. It possesses a 325RLDRD329 motif, which is highly conserved and plays an important role in fructose binding. The predicted three-dimensional active-site structure of SI was superimposed on and compared with those of other α-glucosidases in family 13. We identified two Arg residues that may play important roles in SI-substrate binding with weak ionic strength. Mutations at Arg325 and Arg328 in the fructose-binding site reduced isomaltulose production and slightly increased trehalulose production. In addition, the perturbed interactions between the mutated residues and fructose at the fructose-binding site seemed to have altered the binding affinity of the site, where glucose could now bind and be utilized as a second substrate for isomaltose production. From eight mutant enzymes designed based on structural analysis, the R325Q mutant enzyme exhibiting high relative activity for isomaltose production was selected. We recorded 40.0% relative activity at 15% (wt/vol) additive glucose with no temperature shift; the maximum isomaltose concentration and production yield were 57.9 g liter−1 and 0.55 g of isomaltose/g of sucrose, respectively. Furthermore, isomaltose production increased with temperature but decreased at a temperature of >35°C. Maximum isomaltose production (75.7 g liter−1) was recorded at 35°C, and its yield for the consumed sucrose was 0.61 g g−1 with the addition of 15% (wt/vol) glucose. The relative activity for isomaltose production increased progressively with temperature and reached 45.9% under the same conditions.
PMCID: PMC2519274  PMID: 18552181
17.  Hypoxia-induced IL-18 Increases Hypoxia-inducible Factor-1α Expression through a Rac1-dependent NF-κB Pathway 
Molecular Biology of the Cell  2008;19(2):433-444.
Interleukin-18 (IL-18) plays pivotal roles in linking inflammatory immune responses and tumor progression and metastasis, yet the manner in which this occurs remains to be sufficiently clarified. Here we report that hypoxia induces the transcription and secretion of IL-18, which subsequently induces the expression of hypoxia-inducible factor-1α (HIF-1α). Mechanistically, IL-18 induces HIF-1α through the activity of the GTPase Rac1, which inducibly associates with the IL-18 receptor β (IL-18Rβ) subunit, via a PI3K-AKT-NF-κB–dependent pathway. Importantly, the knockdown of the IL-18Rβ subunit inhibited IL-18–driven tumor cell metastasis. Collectively, these findings demonstrate a feed-forward pathway in HIF-1α–mediated tumor progression, in which the induction of IL-18 by hypoxia or inflammatory cells augments the expression of both HIF-1α and tumor cell metastasis.
PMCID: PMC2230593  PMID: 18003981
18.  noxin, a Novel Stress-Induced Gene Involved in Cell Cycle and Apoptosis▿  
Molecular and Cellular Biology  2007;27(15):5430-5444.
We describe a novel stress-induced gene, noxin, and a knockout mouse line with an inactivated noxin gene. The noxin gene does not have sequelogs in the genome and encodes a highly serine-rich protein with predicted phosphorylation sites for ATM, Akt, and DNA-dependent protein kinase kinases; nuclear localization signals; and a Zn finger domain. noxin mRNA and protein levels are under tight control by the cell cycle. noxin, identified as a nitric oxide-inducible gene, is strongly induced by a wide range of stress signals: γ- and UV irradiation, hydrogen peroxide, adriamycin, and cytokines. This induction is dependent on p53. Noxin accumulates in the nucleus in response to stress and, when ectopically expressed, Noxin arrests the cell cycle at G1; although it also induces p53, the cell cycle arrest function of Noxin is independent of p53 activity. noxin knockout mice are viable and fertile; however, they have an enlarged heart, several altered hematopoietic parameters, and a decreased number of spermatids. Importantly, loss or downregulation of Noxin leads to increased cell death. Our results suggest that Noxin may be a component of the cell defense system: it is activated by various stress stimuli, helps cells to withdraw from cycling, and opposes apoptosis.
PMCID: PMC1952090  PMID: 17515607
19.  Cloning and Characterization of the xyl1 Gene, Encoding an NADH-Preferring Xylose Reductase from Candida parapsilosis, and Its Functional Expression in Candida tropicalis 
Applied and Environmental Microbiology  2003;69(10):6179-6188.
Xylose reductase (XR) is a key enzyme in d-xylose metabolism, catalyzing the reduction of d-xylose to xylitol. An NADH-preferring XR was purified to homogeneity from Candida parapsilosis KFCC-10875, and the xyl1 gene encoding a 324-amino-acid polypeptide with a molecular mass of 36,629 Da was subsequently isolated using internal amino acid sequences and 5′ and 3′ rapid amplification of cDNA ends. The C. parapsilosis XR showed high catalytic efficiency (kcat/Km = 1.46 s−1 mM−1) for d-xylose and showed unusual coenzyme specificity, with greater catalytic efficiency with NADH (kcat/Km = 1.39 × 104 s−1 mM−1) than with NADPH (kcat/Km = 1.27 × 102 s−1 mM−1), unlike all other aldose reductases characterized. Studies of initial velocity and product inhibition suggest that the reaction proceeds via a sequentially ordered Bi Bi mechanism, which is typical of XRs. Candida tropicalis KFCC-10960 has been reported to have the highest xylitol production yield and rate. It has been suggested, however, that NADPH-dependent XRs, including the XR of C. tropicalis, are limited by the coenzyme availability and thus limit the production of xylitol. The C. parapsilosis xyl1 gene was placed under the control of an alcohol dehydrogenase promoter and integrated into the genome of C. tropicalis. The resulting recombinant yeast, C. tropicalis BN-1, showed higher yield and productivity (by 5 and 25%, respectively) than the wild strain and lower production of by-products, thus facilitating the purification process. The XRs partially purified from C. tropicalis BN-1 exhibited dual coenzyme specificity for both NADH and NADPH, indicating the functional expression of the C. parapsilosis xyl1 gene in C. tropicalis BN-1. This is the first report of the cloning of an xyl1 gene encoding an NADH-preferring XR and its functional expression in C. tropicalis, a yeast currently used for industrial production of xylitol.
PMCID: PMC201247  PMID: 14532079
20.  Purification and Characterization of a Novel Mannitol Dehydrogenase from a Newly Isolated Strain of Candida magnoliae 
Mannitol biosynthesis in Candida magnoliae HH-01 (KCCM-10252), a yeast strain that is currently used for the industrial production of mannitol, is catalyzed by mannitol dehydrogenase (MDH) (EC In this study, NAD(P)H-dependent MDH was purified to homogeneity from C. magnoliae HH-01 by ion-exchange chromatography, hydrophobic interaction chromatography, and affinity chromatography. The relative molecular masses of C. magnoliae MDH, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and size-exclusion chromatography, were 35 and 142 kDa, respectively, indicating that the enzyme is a tetramer. This enzyme catalyzed both fructose reduction and mannitol oxidation. The pH and temperature optima for fructose reduction and mannitol oxidation were 7.5 and 37°C and 10.0 and 40°C, respectively. C. magnoliae MDH showed high substrate specificity and high catalytic efficiency (kcat = 823 s−1, Km = 28.0 mM, and kcat/Km = 29.4 mM−1 s−1) for fructose, which may explain the high mannitol production observed in this strain. Initial velocity and product inhibition studies suggest that the reaction proceeds via a sequential ordered Bi Bi mechanism, and C. magnoliae MDH is specific for transferring the 4-pro-S hydrogen of NADPH, which is typical of a short-chain dehydrogenase reductase (SDR). The internal amino acid sequences of C. magnoliae MDH showed a significant homology with SDRs from various sources, indicating that the C. magnoliae MDH is an NAD(P)H-dependent tetrameric SDR. Although MDHs have been purified and characterized from several other sources, C. magnoliae MDH is distinguished from other MDHs by its high substrate specificity and catalytic efficiency for fructose only, which makes C. magnoliae MDH the ideal choice for industrial applications, including enzymatic synthesis of mannitol and salt-tolerant plants.
PMCID: PMC169128  PMID: 12902227
21.  Purification and Characterization of a Novel Erythrose Reductase from Candida magnoliae 
Erythritol biosynthesis is catalyzed by erythrose reductase, which converts erythrose to erythritol. Erythrose reductase, however, has never been characterized in terms of amino acid sequence and kinetics. In this study, NAD(P)H-dependent erythrose reductase was purified to homogeneity from Candida magnoliae KFCC 11023 by ion exchange, gel filtration, affinity chromatography, and preparative electrophoresis. The molecular weights of erythrose reductase determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel filtration chromatography were 38,800 and 79,000, respectively, suggesting that the enzyme is homodimeric. Partial amino acid sequence analysis indicates that the enzyme is closely related to other yeast aldose reductases. C. magnoliae erythrose reductase catalyzes the reduction of various aldehydes. Among aldoses, erythrose was the preferred substrate (Km = 7.9 mM; kcat/Km = 0.73 mM−1 s−1). This enzyme had a dual coenzyme specificity with greater catalytic efficiency with NADH (kcat/Km = 450 mM−1 s−1) than with NADPH (kcat/Km = 5.5 mM−1 s−1), unlike previously characterized aldose reductases, and is specific for transferring the 4-pro-R hydrogen of NADH, which is typical of members of the aldo/keto reductase superfamily. Initial velocity and product inhibition studies are consistent with the hypothesis that the reduction proceeds via a sequential ordered mechanism. The enzyme required sulfhydryl compounds for optimal activity and was strongly inhibited by Cu2+ and quercetin, a strong aldose reductase inhibitor, but was not inhibited by aldehyde reductase inhibitors and did not catalyze the reduction of the substrates for carbonyl reductase. These data indicate that the C. magnoliae erythrose reductase is an NAD(P)H-dependent homodimeric aldose reductase with an unusual dual coenzyme specificity.
PMCID: PMC165123  PMID: 12839736
22.  1,8-Dihydroxynaphthalene (DHN)-Melanin Biosynthesis Inhibitors Increase Erythritol Production in Torula corallina, and DHN-Melanin Inhibits Erythrose Reductase 
The yeast Torula corallina is a strong erythritol producer that is used in the industrial production of erythritol. However, melanin accumulation during culture represents a serious problem for the purification of erythritol from the fermentation broth. Melanin biosynthesis inhibitors such as 3,4-dihydroxyphenylalanine and 1,8-dihydroxynaphthalene (DHN)-melanin inhibitors were added to the T. corallina cultures. Only the DHN-melanin inhibitors showed an effect on melanin production, which suggests that the melanin formed during the culturing of T. corallina is derived from DHN. This finding was confirmed by the detection of a shunt product of the pentaketide pathway, flaviolin, and elemental analysis. Among the DHN-melanin inhibitors, tricyclazole was the most effective. Supplementation with tricyclazole enhanced the production of erythritol while significantly inhibiting the production of DHN-melanin and DHN-melanin biosynthetic enzymes, such as trihydroxynaphthalene reductase. The erythrose reductase from T. corallina was purified to homogeneity by ion-exchange and affinity chromatography. Purified erythrose reductase was significantly inhibited in vitro in a noncompetitive manner by elevated levels of DHN-melanin. In contrast, the level of erythrose reductase activity was unaffected by increasing concentrations of tricyclazole. These results suggest that supplemental tricyclazole reduces the production of DHN-melanin, which may lead to a reduction in the inhibition of erythrose reductase and a higher yield of erythritol. This is the first report to demonstrate that melanin biosynthesis inhibitors increase the production of a sugar alcohol in T. corallina.
PMCID: PMC161539  PMID: 12788746
24.  Fumarate-Mediated Inhibition of Erythrose Reductase, a Key Enzyme for Erythritol Production by Torula corallina 
Torula corallina, a strain presently being used for the industrial production of erythritol, has the highest erythritol yield ever reported for an erythritol-producing microorganism. The increased production of erythritol by Torula corallina with trace elements such as Cu2+ has been thoroughly reported, but the mechanism by which Cu2+ increases the production of erythritol has not been studied. This study demonstrated that supplemental Cu2+ enhanced the production of erythritol, while it significantly decreased the production of a major by-product that accumulates during erythritol fermentation, which was identified as fumarate by instrumental analyses. Erythrose reductase, a key enzyme that converts erythrose to erythritol in T. corallina, was purified to homogeneity by chromatographic methods, including ion-exchange and affinity chromatography. In vitro, purified erythrose reductase was significantly inhibited noncompetitively by increasing the fumarate concentration. In contrast, the enzyme activity remained almost constant regardless of Cu2+ concentration. This suggests that supplemental Cu2+ reduced the production of fumarate, a strong inhibitor of erythrose reductase, which led to less inhibition of erythrose reductase and a high yield of erythritol. This is the first report that suggests catabolite repression by a tricarboxylic acid cycle intermediate in T. corallina.
PMCID: PMC124133  PMID: 12200310

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