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Biomedical subjects

S C Kuo

Publications and source records attributed to S C Kuo.

At least 127 records · Page 7Linked to original sources
PubMed1975

Action of cytochalasin A, a sulfhydryl-reactive agent, on sugar metabolism and membrane-bound adenosine triphosphatase of yeast.

Cytochalasin A at 10-20 mug/ml inhibits growth and sugar uptake by Saccharomyces strain 1016. The effects of cytochalasin A in intact cells were completely prevented when 1 mM cysteine or dithiothreitol was added along with cytochalasin A, but were not eliminated by thiols added after inhibition had occurred. Purified yeast hexokinase, glucose-6-P dehydrogenase, phosphofructokinase and aldolase were not sensitive to cytochalasin A (20 mug/ml). Glyceraldehyde-3-P dehydrogenase was strongly inhibited by cytochalasin A (5 mug/ml); activity was promptly restored by thiols. Anaerobic glycolysis was inhibited by cytochalasin A or by iodoacetate; unlike iodoacetate, cytochalasin A did not cause accumulation of sugar phosphates. In contrast, cytochalasin A, but not iodoacetate, inhibited isolated membrane-bound ATPases. Cytochalasin A is a sulfhydryl-reactive agent and has membrane-related effects (adenosine triphosphatase) which may well be the basis of its interference with energy-dependent uptake of solutes.

Adenosine Triphosphatases↗
PubMed1973

Lomofungin, an inhibitor of deoxyribonucleic acid-dependent ribonucleic acid polymerases.

Lomofungin, an antibiotic active against fungi, yeasts, and bacteria, was found to be a potent inhibitor of purified Escherichia coli deoxyribonucleic acid (DNA)-dependent ribonucleic acid (RNA) polymerase. It prevents RNA synthesis by a direct interaction with the polymerase and not with the template or substrate; chain elongation is halted promptly. Three DNA-dependent RNA polymerases isolated from Saccharomyces strain 1016 were also sensitive to the antibiotic. Lomofungin does not appear to react generally with proteins, as bovine serum albumin did not prevent the inhibitory effect and numerous other enzymes were not affected by lomofungin.

Antifungal Agents↗
PubMed1973

Saccharomyces mutants with invertase formation resistant to repression by hexoses.

Production of invertase by many strains of yeast is repressed in the presence of hexoses. This phenomenon interferes with studies on the secretion of invertase and with the preparation of large quantities of the enzyme for examination of its chemical and physical characteristics. Saccharomyces strain 303-67, a diploid carrying the single gene SUC-2 for (hexose repressible) invertase production, was subjected to ultraviolet irradiation. No single-step mutations to high level resistance were detected. By a two-step irradiation process mutants were obtained with differing degrees of resistance. The biochemical and genetic characteristics of these mutants are summarized with particular emphasis on FH4C (the most resistant). Although the steady state level of cyclic 3', 5'-adenosine monophosphate (cyclic AMP) was usually slightly higher in cells grown in low- rather than in high-glucose media, the level of cyclic AMP was not correlated with the sensitivity of invertase synthesis to glucose repression. In mutant FH4C, 1 to 2% of the total cell protein is present as invertase; synthesis of alpha-glucosidase is also resistant to repression by hexoses. This mutant does not sporulate and is probably a haploid of a-mating type with low frequency of conjugation and poor viability of conjugants. Mutants 1016 and 1710 are substantially resistant to hexose repression and still sporulate well. They may be useful for genetic analysis of hexose resistance.

Culture Media↗
PubMed1972

Inhibition by 2-deoxy-D-glucose of synthesis of glycoprotein enzymes by protoplasts of Saccharomyces: relation to inhibition of sugar uptake and metabolism.

The synthesis of the glycoprotein enzymes, invertase and acid phosphatase, by protoplasts of Saccharomyces mutant 1016, is inhibited by 2-deoxy-d-glucose (2-dG) after a 20- to 30-min lag period under conditions (external sugar to 2-dG ratio of 40:1) which cause only a slight decrease in total protein synthesis. Formation of one intracellular enzyme, alpha-glucosidase, is also sensitive, but production of another, alkaline phosphatase, is unaffected. A nonmetabolized glucose analogue, 6-deoxy-d-glucose, had no inhibitory effect. The total uptake of external fructose and maltose was decreased by 2-dG after a lag period of about the same duration as that before the inhibition of synthesis of enzymes or of mannan and glucan; during this time 2-dG was taken up by the protoplasts and accumulated primarily as 2-dG-6-phosphate (2-dG-6-P). Studies in vitro showed that 2-dG-6-P inhibits both yeast phosphoglucose isomerase and phosphomannose isomerase. The intracellular levels of the 6-phosphates of glucose, fructose, and mannose did not increase in the presence of 2-dG. We suggest that the high internal level of 2-dG-6-P blocks synthesis of the cell wall polysaccharides and glycoproteins in two ways. It directly inhibits the conversion of fructose-6-P to glucose-6-P and to mannose-6-P. At the same time, it restricts the transport of fructose and maltose into the cell; however, the continuing limited uptake of the sugars still provides sufficient energy for protein synthesis. The cessation of alpha-glucosidase synthesis is probably a result of depletion of the internal pool of maltose (the inducer). Our findings support the suggestion that restriction of synthesis of the carbohydrate moiety of glycoproteins reduces formation of the active enzyme.

Acid Phosphatase↗
PubMed1971

Osmotic regulation of invertase formation and secretion by protoplasts of Saccharomyces.

Osmotic regulation of invertase formation and secretion by protoplasts of Saccharomyces was examined using sorbitol, KCl, NaCl, or magnesium sulfate as the osmotic support. The synthesis and secretion of the enzyme is remarkably sensitive to the osmolarity of the supporting medium irrespective of the particular support employed. Invertase formation was inhibited at high osmolarity and was maximal at 0.65 to 0.75 osmolal, even though some leakage of the intracellular enzyme alpha-glucosidase and of ultraviolet (UV)-absorbing materials occurred under these conditions. The reduction of invertase formation and secretion due to high osmolarity was eliminated promptly when protoplasts were transferred into a medium of lower osmolarity. The rate of fructose uptake and of threonine incorporation into protein was decreased by high osmolarity; also reduction of invertase formation could be partially reversed by increasing the level of sugar supplied as energy source. Thus changes in the permeability of the plasma membrane (and presumably also in its structure) are important factors in the response of protoplasts to high osmolarity, though certainly not the complete explanation. Protoplasts suspended in 0.8 m sorbitol, with 10mm fructose as the energy source, increased their invertase level 5- to 10-fold during a 2-hr incubation without substantial release of alpha-glucosidase or UV-absorbing materials. Both the large and small forms of invertase were present in the protoplasts, but only the large form was released into the medium when enzyme was being actively synthesized. Formation and secretion of newly formed invertase and the release of enzyme initially present were inhibited by cycloheximide.

Absorption↗
PubMed1971

Production of phenotypically epimeraseless yeast by L-arabinose.

The previous report from this laboratory that l-arabinose is a gratuitous inducer of the galactose transport system has been found to be an artefact resulting from the combination of galactose contamination of commercial samples of l-arabinose and inhibition by l-arabinose of galactose metabolism by inactivation of uridine-diphosphate-glucose-4-epimerase. As a result of l-arabinose inhibition of the metabolism of the contaminating galactose, galactose itself serves as a gratuitous inducer, producing phenotypically epimeraseless yeast.

Arabinose↗
PubMed1970

Galactose transport in Saccharomyces cerevisiae. 3. Characteristics of galactose uptake in transferaseless cells: evidence against transport-associated phosphorylation.

The characteristics of the inducible galactose transport system in bakers' yeast were studied in uridine diphosphate, galactose-1-phosphate uridylyl-transferaseless cells. Transferaseless cells transport galactose at the same initial rate as wild-type cells and accumulate a mixture of free galactose and galactose-1-phosphate. The addition of (14)C-labeled galactose to cells preloaded with unlabeled galactose and galactose-1-phosphate results in a higher rate of labeling of the free-sugar pool than of the galactose-1-phosphate pool. These results support other evidence that galactose uptake in bakers' yeast is a carrier-mediated, facilitated diffusion and that phosphorylation is an intracellular event after uptake of the free sugar.

Biological Transport↗
PubMed1969

Capacity of aspartic acid to increase the bacterial count on suspensions of Escherichia coli after freezing.

The addition of 2% Trypticase to a minimal salts-glucose plating medium increased the bacterial count of frozen and thawed suspensions of Escherichia coli 451B cells, even when precautions were taken to remove toxic trace elements from the plating diluent. Hydrolysis of the Trypticase with HCl or H(2)SO(4) reduced its count-increasing activity. Treatment of the H(2)SO(4) hydrolysate with a cation-exchange resin greatly improved its capacity to replace Trypticase. Addition of a mixture of amino acids approximating the composition of casein also increased the plate count when added at a level equivalent to 0.1% casein, but at 2% it depressed the count. Tests of amino acids in the mixture revealed that aspartic acid could replace Trypticase completely as a supplement to the basal medium. When added at a level of 2.5 mm, aspartic acid doubled and occasionally tripled the plate count of a suspension of frozen and thawed cells. Glutamic acid, alanine, and to a lesser extent certain other amino acids also showed a capacity to increase the count. Cysteine was without significant effect. Serine and other amino acids depressed the count. None of the amino acids or other supplements affected the count of suspensions of cells that had not been frozen. The effect of adding aspartic acid, cysteine, or Trypticase to the basal medium on the bacterial count of suspensions of various strains of E. coli, Aerobacter aerogenes, Serratia marcescens, and two species of Pseudomonas after freezing was examined. The response to the supplements was unique for each organism.

Acetates↗
PubMed1967

Metabolic injury to bacteria. II. Metabolic injury induced by distilled water or Cu++ in the plating diluent.

When distilled water from a tin-lined still served as the plating diluent, cells of Aerobacter aerogenes developed symptoms of metabolic injury as evidenced by increased counts on supplemented, as compared with minimal, plating medium. Cysteine was as effective as yeast extract as a supplement to the minimal medium in increasing the viable count. Mg(++) and, to a lesser extent, phosphate buffer at the concentrations tested protected unfrozen cells, but not cells which had been frozen and stored, against the loss of capacity to grow on minimal medium. When the plating diluent consisted of distilled water redistilled in an all-glass still, the symptoms of metabolic injury did not appear. Spectrographic analysis revealed the presence of 10(-7)m Cu(++) in the distilled water, and Cu(++) added to redistilled water serving as the plating diluent reproduced the metabolic injury effects induced by distilled water. It was concluded that freezing and storage damaged the cell membrane, rendering it more penetrable by toxic elements which were thereby enabled to act at sites in the cell where Mg(++) and other solutes in the plating diluent could not serve as effective antagonists. Increased recovery of cells on supplemented medium could be ascribed to the capacity of the supplements to remove toxic elements which had become bound to the cells during suspension in the plating diluent.

Buffers↗
PubMedDate not supplied

Ibuprofen affects arylamine N-acetyltransferase activity in Helicobacter pylori from peptic ulcer patients.

Arylamine N-acetyltransferase (NAT) activities with 2-aminofluorene and p-aminobenzoic acid were determined in the bacterium Helicobacter pylori collected from peptic ulcer patients. Cytosols or suspensions of H. pylori with or without specific concentrations of ibuprofen co-treatment showed different percentages of 2-aminofluorene and p-aminobenzoic acid acetylation. The data indicate that there was decreased NAT activity associated with increased levels of ibuprofen in H. pylori cytosols. Inhibition of growth studies on H. pylori demonstrated that ibuprofen elicited a dose-dependent bactericide effect in H. pylori cultures, i.e. the greater the concentration of ibuprofen, the greater the inhibition of growth to H. pylori. For the cytosol and intact bacteria examinations, the apparent values of Km and Vmax were decreased after co-treatment with 40 microM ibuprofen. This report is the first demonstration of ibuprofen inhibition of arylamine N-acetyltransferase activity and ibuprofen inhibition of growth in the bacterium H. pylori.

Arylamine N-Acetyltransferase↗
PubMedDate not supplied

[Educational effects of a short-term diabetes camp for children].

A Diabetes camp provides children with fun and educational experience. Seventeen diabetic school children (12 boys and 5 girls) participated in a short-term diabetes camp from April 16 to 17, 1988. Their ages ranged from 8.5 to 13.2 years with an average of 11.3 +/- 1.5 (mean +/- SD) years. The duration of their diabetes varied from 0.05 to 5.3 years with an average of 2.7 +/- 3.3 years. The camp staff consisted of a pediatric endocrinologist, 3 nurses, 4 dietitians, 3 social workers, 4 assistant diabetes educators, and 2 counsellors who were specialized in music and recreational activities. The children's abilities in managing their diabetes were assessed by using a scoring system before and after the camping. Wilcoxon matched-pairs signed-rank tests with significance levels set at p < 0.05 (two-tailed) were conducted to determine whether there were any significant changes in the results from pre- and postcamp assessments. The children showed significant improvement in using glucose-monitoring devices, drawing insulin, injecting insulin, and choosing the right exchange of food with the p values of less than 0.05, 0.01, 0.01, and 0.01 respectively. We concluded that this short-term diabetes camp was educational for school children with diabetes. The campers improved their knowledge and skill in management of diabetes.

Adolescent↗