Biomedical subjects

S Y Choi

Publications and source records attributed to S Y Choi.

At least 145 records · Page 8Linked to original sources

PubMed1993

High level expression in Saccharomyces cerevisiae of an artificial gene encoding a repeated tripeptide aspartyl-phenylyalanyl-lysine.

A chemically synthesized gene, which encodes a 64 or 128 times-repeated tripeptide, aspartyl-phenylalanyl-lysine, has been cloned onto the yeast expression vector pAM82 containing the PHO5 promoter. The artificial gene (LAP gene) contains the untranslated leader sequence of the E. coli lipoprotein gene (lpp) with its transcription terminator sequence. When yeast AH22 cells transformed by recombinant plasmid containing repeated tripeptide gene were derepressed in low phosphate medium, the artificial polypeptides were synthesized to the amounts of about 30% of the total cell protein. SDS-polyacrylamide gel electrophoresis and immunoblot analysis indicated that the artificial polypeptides synthesized in yeast have molecular weights ranging from about 30,000 and 60,000 and have immunoreactivity with the artificial polypeptides expressed in E. coli. The artificial popypeptides in whole cell extract were insoluble and seem to be synthesized as insoluble aggregates. Electron microscopy showed the presence of inclusion bodies in the cell. These polypeptides can be hydrolyzed to tripeptides with trypsin or chymotrypsin. These properties along with the high expression and easy separation may make the artificial polypeptides a potential raw material for the production of an artificial sweetener, Aspartame.

Amino Acid Sequence↗

PubMed1993

Molecular analysis of three maize 22 kDa auxin-binding protein genes--transient promoter expression and regulatory regions.

The site I 22 kDa auxin-binding proteins from maize are encoded by a small gene family comprising at least five members. Here the cloning and molecular analysis of the Zm-ERabp1, Zm-ERabp4, and Zm-ERabp5 genes is presented. All three encode 22-23 kDa proteins displaying a transit peptide, a C-terminal KDEL sequence, as well as glycosylation and auxin-binding sites. The Zm-ERabp4 and Zm-ERabp5 genes are very similar. The Zm-ERabp1 gene encodes a related protein, but its promoter, leader and signal peptide are very different. Northern analysis using gene-specific oligonucleotide probes indicates that Zm-ERabp4 is expressed in leaves and coleoptiles but weakly in roots, whereas Zm-ERabp5 expression is barely detectable in these tissues. RNA-PCR indicated that all three genes are none the less expressed in many tissues. Primer-extension analysis revealed an unusually long (320 bases) Zm-ERabp1 leader containing an 80 codon ORF which, if expressed, would encode a positively charged protein with some similarity to transcription factors. In a transient promoter-reporter gene expression system using maize leaf protoplasts the Zm-ERabp1 promoter is more active than the Zm-ERabp4 and Zm-ERabp5 promoters. Promoter deletion analysis of Zm-ERabp1 has identified a negative regulatory sequence in a region from -364 bp and -130 bp, deletion of which results in about twofold higher expression. This region contains both enhancer- and G-box-related sequences. Deletion of -126 bp to +64 bp, which contains the TATA box and transcription start, results in a large decrease in expression.

Amino Acid Sequence↗

PubMed1993

Effect of a collagen matrix on healing in periodontal fenestration defects in dogs.

Contralateral periodontal fenestration defects in seven beagle dogs were used to evaluate influence of a collagen matrix on periodontal wound healing. The defects (6 x 4 mm) were created through the buccal cortical plates of the maxillary canine teeth following elevation of mucoperiosteal flaps. The collagen was fitted to the defects on one side. Contralateral defects served as controls. Flaps were repositioned and sutured. Dogs were sacrificed 4 weeks after surgery and block sections including teeth and surrounding structures were prepared for histometric analysis. No meaningful differences in cementum and bone regeneration were observed between treatments. There was seemingly more bone regeneration in the apical than in the coronal aspect of the defects and significantly more cementum regeneration. Root resorption was observed in one collagen and one control defect. Ankylosis was not observed. The results suggest that the maxillary canine periodontal fenestration defect can be used as a model to evaluate factors that may enhance cementum and bone regeneration. The collagen matrix neither enhanced nor inhibited periodontal wound healing in this model.

Alveolar Bone Loss↗

PubMed1992

Properties of aspartate racemase, a pyridoxal 5'-phosphate-independent amino acid racemase.

Aspartate racemase from Streptococcus thermophilus contains no pyridoxal 5'-phosphate or other cofactors such as FAD, NAD+, and metal ions. It was affected by neither carbonyl reagents such as hydroxylamine nor sodium borohydride but was strongly inhibited by iodoacetamide and other thiol reagents. Aspartate, cysteate, and cysteine sulfinate were the only substrates. The Km values for L- and D-aspartate were 35 and 8.7 mM, respectively. The enzyme catalyzed the exchange of alpha-hydrogen of the substrate with the solvent hydrogen. Racemization of L-aspartate in 2H2O showed an overshooting in the optical rotation of aspartate before the substrate was fully racemized. This shows that the removal of alpha-hydrogen of the substrate is at least partially rate-determining. When L- or D-aspartate was incubated with aspartate racemase in tritiated water, tritium was incorporated preferentially into the product enantiomer. The results strongly suggest that aspartate racemase contains two hydrogen acceptors.

Amino Acid Isomerases↗

PubMed1992

Stimulation of protein synthesis in COS cells transfected with variants of the alpha-subunit of initiation factor eIF-2.

The role of eukaryotic initiation factor 2 (eIF-2) phosphorylation in translational control has been demonstrated in vivo by overexpressing variant forms of eIF-2 alpha that are not phosphorylated. COS-1 cells transiently transfected with expression vectors for human eIF-2 alpha contain 10-20-fold more eIF-2 alpha subunit than the endogenous COS cell eIF-2 trimeric complex. Expression of the variant form of eIF-2 alpha, Ser51Asp, where Asp replaces Ser51, causes inhibition of protein synthesis, whereas the Ser48Asp variant does not. When either Ser48 or Ser51 is replaced by Ala, the variants stimulate dihydrofolate reductase synthesis when the eIF-2 alpha kinase, DAI, is activated. In order to elucidate these mechanisms, we have separated eIF-2 trimeric complexes from free overexpressed eIF-2 alpha subunits by fast protein liquid chromatography Superose chromatography. Pulse-labeled cells transfected with wild-type or variant DNAs produced eIF-2 preparations with greater than 10-fold higher specific radioactivity in the alpha-subunit compared to the gamma-subunit, thus demonstrating that the human eIF-2 alpha produced from the plasmids readily exchanges into COS cell eIF-2 complexes. Both wild-type and Ser48Ala variant forms of the free 2 alpha-subunit, further purified by MonoQ chromatography, are poor substrates for the heme-regulated eIF-2 alpha kinase, HRI, but are good substrates for double-stranded RNA-activated inhibitor in vitro; the Ser51Ala variant subunit is not phosphorylated by either kinase. None of the purified free eIF-2 alpha subunits inhibits phosphorylation of eIF-2 in vitro, even at up to 8-fold molar excess. Examination of the extent of eIF-2 alpha phosphorylation in the COS cell eIF-2 complexes by two-dimensional polyacrylamide gel electrophoresis shows that the stimulation of dihydrofolate reductase synthesis by the Ser51Ala variant is most readily explained by failure of eIF-2 to be phosphorylated. Stimulation by the Ser48Ala variant appears to occur by mitigation of the effect of phosphorylation at Ser51 since the double variant, Ser48Ala-Ser51Asp, inhibits protein synthesis less than the single variant Ser51Asp. The evidence argues strongly against there being a second site of phosphorylation involved in translational repression.

Base Sequence↗

PubMed1992

Allotypes of the fourth component of complement in Koreans.

The analysis of genetic polymorphism in C4 was performed on EDTA-plasma from 169 healthy unrelated Koreans. Plasma samples were subjected to high-voltage agarose gel electrophoresis followed by immunofixation. C4B allotypes were further detected by a hemolytic overlay method. The allele frequencies of C4A and C4B were as follows; for C4A, C4A*3 = 0.6099, C4A*4 = 0.1702, C4A*Q0 = 0.1525, C4A*2 = 0.0461, and C4A*R = 0.0213; for C4B, C4B*1 = 0.6406, C4B*2 = 0.2740, C4B*5 = 0.0569, C4B*Q0 = 0.0178, and C4B*R = 0.0107. C4A*3 and C4B*1 were among the most common alleles at each locus. C4A*6 was not detected in this study, but this allele is relatively common in both Caucasoid and Negroid populations. C4B*5 is a common allele in Asian, which is rare in Caucasoids and Negroids. C4B*5 appeared to be a characteristic allele of Oriental. In the C4A locus, five individuals with duplicated allotypes (three C4A 3,3 + 2, one C4A 4,3 + 2, and one C4A 3,3 + 3) were observed, and in the C4B locus, one individual with duplicated allotype (C4B 1,1 + 1) was detected.

Alleles↗

PubMed1992

Reaction mechanism of glutamate racemase, a pyridoxal phosphate-independent amino acid racemase.

Glutamate racemase of Pediococcus pentosaceus contained no cofactor, and was completely inactivated by a thiol reagent. The role of a cysteine residue in the enzyme reaction was studied by chemical modification. The modification of this cysteine residue resulted in a concomitant loss of activity. DL-Glutamate protected the enzyme from inactivation. The inactivated enzyme was reactivated by addition of dithiothreitol. The racemization in 2H2O showed an overshoot in the optical rotation of glutamate before the substrate was completely racemized. This indicates that the removal of alpha-hydrogen is the rate determining step. During the racemization of D- or L-glutamate in 3H2O, tritium was incorporated preferentially into the product. Glutamate is racemized by the enzyme probably through a two base mechanism.

Amino Acid Isomerases↗

PubMed1992

Surgical treatment of periampullary cancer--review of 766 surgical experiences of 8 hospitals.

The incidence of periampullary cancer has been steadily rising in Korea. In the present study, we have reviewed 766 cases of surgically treated periampullary cancers, including 122 cases of our own, which were published in the Korean literature from 1984 to 1992. The 6th decade was the most prevalent age group, occupying 38% of the patients. The ratio of male of female was 1.7 to 1. Approximately 60% of lesion located at the head of the pancreas. Computed tomography which had 85% sensitivity was the most commonly employed modality for a diagnosis. The diagnostic sensitivity of percutaneous transhepatic cholangiography was 72%, of endoscopic retrograde cholangiopancreatography was 71%, and of ultrasonography was 54% in order of frequency. Tumor markers such as CA-19, CEA, and CA-125 were also studied in pancreatic cancer. The combinations of these markers recorded a higher positivity than using solely. The resection rate for lesions at the head of the pancreas was 21%, and that of distal common bile duct, ampulla of vater, and duodenum were 37%, 85%, and 50%, respectively. The morbidity and mortality rates after pancreatoduodenectomy were 44% and 12%, respectively. TNM staging revealed 66% of patients were in stage III, 26% in stage I, and 8% in stage II. The actual 5-year survival rates for cancer of the head of the pancreas was 11%, and that of duodenal cancer, distal choledochal cancer, and ampullary cancer were 21%, 18%, and 15%, respectively. In nonresected group, none survived over 18 months after treatment. Relatively high portion of lymph node metastatic patients may explain the poor survival observed in our series.

Ampulla of Vater↗

PubMed1992

Growth in overcrowded housing: a comparison of the states.

"The present article reports on a research project that is seeking greater understanding of the prevalence of overcrowding [in the United States] and its causes. First we review the definition of overcrowding and describe differences between renters and owners. Next we document the state-by-state variation in crowding levels among renters. Then we explore some of the factors that may explain this variation."

Americas↗

PubMed1992

Brain glutamate decarboxylase and pyrroloquinoline quinone.

Porcine brain glutamate decarboxylase was examined for the presence of covalently bound pyrroloquinoline quinone (PQQ). HPLC analysis of pure glutamate decarboxylase subjected to the hexanol extraction procedure gave negative results when monitored at 320 nm, the maximum of absorbance of 4-hydroxy-5-hexoxy-PQQ. Resolved glutamate decarboxylase exhibits a structureless absorption band at wavelengths longer than 300 nm which cannot be attributed to PQQ. The holoenzyme is not a pyridoxal-quinoprotein; its catalytic mechanism involves the participation of only one cofactor, i.e. pyridoxal-5-P. Free PQQ is a strong inhibitor of the decarboxylase (Ki = 13 microM) and the reaction with the protein results in spectral changes resembling those of polylysine treated with PQQ. If the concentration of free PQQ in some regions of the brain reaches the micromolar level, then PQQ might play a role in the regulation of glutamate decarboxylase activity.

Animals↗

PubMed1991

Effect of cigarette smoking and alcohol consumption in the etiology of cancers of the digestive tract.

This study presents the comparative patterns of risk of selected digestive tract cancers (esophagus, stomach, colon, rectum and liver) for males in relation to cigarette smoking and alcohol drinking, based on the data from case-control studies conducted in the Korea Cancer Center Hospital (KCCH). There was strong positive association between cigarette smoking and esophageal cancer, but none of the other sites was significantly related to cigarette smoking. In esophageal cancer, a dose-dependent effect for cigarette smoking was observed, with the odds ratio ranging from 1.29 for ever smoking up to 1 pack daily to 3.17 for smokers of more than 2 packs per day. The risk declined markedly following cessation of smoking. Cancers of the esophagus, rectum and liver were strongly related to alcohol consumption. Compared with non-drinkers, the OR for heavy drinkers was 9.14 in esophageal cancer, 4.75 in rectal cancer and 2.46 in liver cancer. In cancer of the stomach and colon, however, there was no association with alcohol drinking.

Alcohol Drinking↗

PubMed1991

The mitochondrial ATP synthase of Trypanosoma brucei: developmental regulation through the life cycle.

The mitochondrial H(+)-ATPase of the parasitic protozoan Trypanosoma brucei is shown to be developmentally regulated through the T. brucei life cycle as has been shown for components of the mitochondrial electron transport chain. We have substantiated our results by assaying not only for oligomycin-sensitive ATPase activity but also by determining the level of ATP synthetic activity. These results show that the level of ATPase present in the procyclic form of T. brucei is increased by at least threefold from that of the early bloodstream form while the ATPase activity in the late bloodstream form is only about twofold higher than the early form. ATP synthesis activity shows these same results. We have determined the level of ATP synthase protein present in the life cycle stages by Western analysis employing the antibodies that we have raised against both the water soluble F1 and the membrane-associated F0 moieties which we have purified from T. brucei. The Western blots of the procyclic form show strong reactivity with both the F0 and F1 antibodies. The other two life cycle stages, the early and the late bloodstream forms, show considerably less reactivity, paralleling the activity results. Electron micrographs of the sonicated mitochondrial fraction show inverted vesicles which are studded with knobby H(+)-ATPase in the procyclic form. The early bloodstream vesicles show very few of these characteristic structures, while the late bloodstream form shows a range of vesicles from nearly nude to partially studded.

Adenosine Triphosphatases↗

PubMed1991

Overproduction of glutamate racemase of Pediococcus pentosaceus in Escherichia coli clone cells and its purification.

We previously isolated a 6.0-kb DNA fragment that specifies glutamate racemase activity from the chromosomal DNA of Pediococcus pentosaceus by digestion with HindIII (N. Nakajima, K. Tanizawa, H. Tanaka, and K. Soda, 1986), Agric. Biol. Chem. 50, 2823-2830). We digested it further with EcoRI to obtain a fragment of 1.8 kb, which was blunt-ended and ligated into the SmaI site of vector plasmid pKK223-3. The recombinant plasmid showed a high glutamate racemase activity upon transformation of Escherichia coli W3110 cells with it; the plasmid was named pICR223. Glutamate racemase was overproduced in the clone cells and occurred in inclusion bodies in the cells. The enzyme was solubilized with 6 M urea, renatured by dialysis to remove urea, and purified to homogeneity with an overall yield of about 70% after a single DEAE-cellulose column chromatography. The amount of enzyme produced by the clone cells corresponded to about 38% of the total insoluble protein.

Amino Acid Isomerases↗

PubMed1991

Effect of cigarette smoking and alcohol consumption in the aetiology of cancer of the oral cavity, pharynx and larynx.

This study presents a comparative risk pattern for cancer of the oral cavity, pharynx and larynx, in relation to cigarette smoking and alcohol consumption based on data from case-control studies conducted in Korea Cancer Center Hospital, Seoul, Korea. The risk of cancer of the oral cavity, pharynx and larynx rose for current smokers and declined for ex-smokers. In males the odds ratios (ORs) for these sites rose with duration of smoking and number of cigarettes smoked per day. The relationship is strongest for laryngeal cancer. The risk for all sites was elevated linearly as amount and frequency of alcohol intake increased. Heavy drinkers, i.e. males who drank 90 g ethanol daily had an approximately 15-fold risk of cancer of the oral cavity, an 11-fold risk of pharyngeal cancer and an 11-fold risk of laryngeal cancer compared with non-drinkers. Alcohol drinking was a much stronger risk factor for cancer of the oral cavity than cancer of the pharynx and larynx. Alcohol was a much weaker risk factor for laryngeal cancer than cigarette smoking. Cancer of the oral cavity, pharynx and larynx also showed an interaction between smoking and alcohol, suggesting a synergistic effect.

Adult↗

PubMed1991

Absorption of short-chain fatty acids from the rat cecum in vivo.

Absorption of the short-chain fatty acids (SCFA), acetate, propionate and butyrate, was studied in vivo by measuring their disappearance from the washed cecum of anesthetized rats. The SCFA seemed to be absorbed predominantly by simple passive diffusion, because there was linear absorption over a wide concentration range, and no evidence of competition or enhancement of absorption when more than one SCFA was present in the lumen. Absorption of these three SCFA was independent of chain length. Their absorption was clearly limited by the lipid membrane, because permeability through the unstirred water layers was much greater than through the lipid membrane. Absorption was unaffected by altering the pH of the luminal infusate between 5.4 and 7.4. Based on our observation that, during absorption, there were increases in pH, total CO2 and HCO3- but no change in pCO2, we suggest that SCFA are absorbed primarily via diffusion involving anionic exchange with HCO3-.

Acetates↗

PubMed1991

Use of an anti-low density lipoprotein receptor antibody to quantify the role of the LDL receptor in the removal of chylomicron remnants in the mouse in vivo.

Lipoproteins are removed from the plasma by LDL receptor-dependent and -independent pathways. The relative contribution of these has been established for LDL by using modified lipoproteins, but this has not been possible for apoE-rich lipoproteins, such as chylomicron remnants. To do this, we used a monospecific antibody to the rat LDL receptor. The antibody was injected intravenously into mice followed by 125I-lipoproteins. Blood samples were obtained sequentially and radioactivity measured to determine the plasma clearance of the lipoproteins. The animals were then sacrificed and the tissues removed, dried, and the radioactivity measured to determine tissue uptake. An albumin space was also measured to correct for blood trapping. With 125I-human LDL, approximately 50% of the injected dose was cleared in 180 min. This was reduced to 30% by the antibody and this was identical to the disappearance of reductively methylated LDL. This is a lower estimate of LDL-mediated uptake (40%) than in other species. LDL uptake per gram tissue was similar for the liver and the adrenal gland and was approximately 50% LDL receptor-dependent in both tissues. With 125I-chylomicron remnants, clearance was much more rapid with approximately 50% cleared in 5 min. By agarose gel electrophoresis, radioactivity was not transferred from chylomicron remnants to other lipoprotein classes. Chylomicron remnants with label on only apoB or in 3H-cholesterol esters showed a similar pattern. Combining the estimates of the three labeling procedures, approximately 35% of the 30 s and 25% of the 5 min chylomicron remnant disappearance was LDL receptor dependent. The liver, per gram tissue, took up five times as much radioactivity as the adrenal gland. At 5 min, at least 50% of this was LDL receptor-dependent in liver and 65% in adrenal gland. We conclude that the LDL receptor plays a major, and somewhat similar quantitative role in the clearance of both LDL and chylomicron remnants in the mouse. However, at least in the mouse, non-LDL receptor-mediated lipoprotein clearance is quantitatively important and is also very rapid for chylomicron remnants. Thus, for chylomicron remnants, it can easily compensate for LDL receptors if they are blocked or absent. Further, the tissue distribution of lipoprotein uptake may be directed by factors other than LDL receptor density.

Animals↗

PubMed1991

Hepatocellular carcinoma in extrahepatic bile ducts.

An elongated solid lesion observed on ultrasonography and CT in the biliary tree causing a smooth filling defect on cholangiography was observed in 2 patients. No tumor was observed in the liver parenchyma either on radiography or at operation. Histopathology showed hepatocellular carcinoma. After removal of the intraductal tumors, recurrence was observed in 2 and 6 months, respectively.

Adult↗

PubMed1990

A case-control study of ginseng intake and cancer.

The effect of ginseng consumption on the risk of cancer was investigated by interviewing 905 pairs of cases and controls matched by age, sex, and date of admission to the Korea Cancer Center Hospital, Seoul, Korea. Of the 905 cases 562 (62%) had a history of ginseng intake compared to 674 of the 905 controls (75%) a statistically significant difference (p less than 0.01). The odds ratio (OR) of cancer in relation to ginseng intake was 0.56 (95% confidence interval (CI), 0.45-0.69). Ginseng extract and powder were shown to be more effective than fresh sliced ginseng, the juice, or tea in reducing the OR. Odds ratios for decreasing levels of ginseng intake were 1.00, 0.58, 0.43 and 0.25 for males and 1.00, 0.81, 0.56 and 0.52 for females. A trend test showed a significant decrease in proportion of cancer cases with increasing frequency of intake for males (p less than 10(-5)) as well as for females (p less than 0.05). Chi-square homogeneity tests also confirmed significant differences between cases and controls for both sexes (p less than 10(-3)). The reliability of recall for ginseng use was assessed by interviewing 180 randomly-selected subjects twice using the same questionnaire. The overall agreement in reported ginseng use between the two interviews was 0.85, and the Kappa value was 0.71 (p less than 0.01). These results strongly support the hypothesis of preventive effects of ginseng on cancer suggested by earlier animal studies.

Adult↗