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Y T Yang

Publications and source records attributed to Y T Yang.

At least 37 records · Page 2Linked to original sources
PubMed2000

Potent antagonists of gonadotropin releasing hormone receptors derived from quinolone-6-carboxamides.

SAR studies which focused upon the C-6 position of a recently described series of quinolone gonadotropin releasing hormone antagonists are reported. Synthetic access to diverse quinolone-6-carboxamides was achieved via the palladium-catalyzed amino-carbonylation reactions of iodide 4 with various amines. Amides related to 9y were especially potent, functional antagonists of rat and human GnRH receptors.

Amides↗
PubMed2000

Effect of glucose analog supplementation on metabolic flux distribution in anaerobic chemostat cultures of Escherichia coli.

Previous work in our laboratories investigated the use of methyl alpha-glucoside (alpha-MG), a glucose analog that shares a phosphotransferase system with glucose, to modulate glucose uptake and therefore reduce acetate accumulation. The results of that study showed a significant improvement in batch culture performance and a reduction in acetate excretion without any significant effect on the growth rate in complex medium. The current study investigates the effect of supplementing the culture medium with the glucose analog alpha-MG on the metabolic fluxes of Escherichia coli under anaerobic chemostat conditions at two different dilution rates. Anaerobic chemostat studies utilizing complex media supplemented with glucose or glucose and alpha-MG at dilution rates of 0.1 and 0.4 h(-1), were performed, and the metabolic fluxes were analyzed. It was found that the addition of the glucose analog alpha-MG has an effect on the specific production rate of various extracellular metabolites. This effect is slightly greater at the higher dilution rate of 0.4 h(-1). However, the glucose analog does not cause any major shift in the central metabolic patterns. It was further observed that alpha-MG supplementation does not result in the reduction in specific acetate synthesis rate in anaerobic chemostat cultures. These results emphasize the importance of testing different strategies for metabolic manipulation under the actual operating conditions.

Anaerobiosis↗
PubMed2000

[Separation and determination of nycodenz and its impurities by capillary electrophoresis].

Separation and determination of nycodenz (a new radiography reagent) and its impurities by capillary electrophoresis was investigated. Since the analytes were polyols, Na2B4O7-H3BO3 was chosen as the buffer system. The analytes were negatively charged by complexing with borate. Then cetyltrimethylammonium bromide was used to reverse electroosmotic mobility in order to shorten the analysis time. 2-Propanol was added to optimize the separation further. Acceptable results of linearity, precision of corrected peak area and migration time were obtained. The RSD(n = 6) of corrected peak area and migration time were 0.73% and 1.4% respectively. The results obtained by CE were directly compared to those obtained by high performance liquid chromatography.

Contrast Media↗
PubMed2000

[Sample preconcentration technique in capillary electrophoresis].

The methods of improving the detection sensitivity in analysis of trace level components by sample preconcentration technique including sample stacking, field-amplified sample injection, isotachophoresis etc. are reviewed, and 67 references are cited.

Electrophoresis, Capillary↗
PubMed1999

Effect of inactivation of nuo and ackA-pta on redistribution of metabolic fluxes in Escherichia coli.

The nuoA-N gene cluster encodes a transmembrane NADH:ubiquinone oxidoreductase (NDH-I) responsible for coupling redox chemistry to proton-motive force generation. Interactions between nuo and the acetate-producing pathway encoded by ackA-pta were investigated by examining the metabolic patterns of several mutant strains under anaerobic growth conditions. In an ackA-pta strain, the flux to acetate was decreased dramatically, whereas flux to lactate was increased significantly when compared with its parent strain; the fluxes to pyruvate and ethanol also increased slightly. In addition, pyruvate was excreted. A strain carrying the nuo mutation showed metabolic flux distribution similar to the wild type. The ackA-pta-nuo strain showed a different metabolic pattern. It not only exhibited reduced acetate accumulation but also significantly lower ethanol and formate synthesis. Metabolic flux distribution analysis suggests that the excessive carbon flux was redirected at the pyruvate node through the lactate dehydrogenase pathway for lactate formation rather than the pyruvate formate-lyase (PFL) pathway for acetyl-CoA and formate production. The diminished capacity through the formate and ethanol (ADH) pathways was not the result of genetic disruption of functional PFL or ADH production. The introduction of a Bacillus subtilis acetolactate synthase gene returned formate, ethanol, and lactate levels to those of the wild type (ackA(+)pta(+)nuo(+)) strain. Furthermore, transfer of a lactate dehydrogenase mutation yielded a strain producing ethanol as the sole fermentation product. As confirmation of the nuo effect, cultures of the ackA-pta strain, supplemented with an NDH-I inhibitor, produced intermediary levels of flux to ethanol and formate. Mutations in both ackA-pta and nuo are required to significantly reduce the flux through the PFL pathway.

Electron Transport Complex I↗
PubMed1999

Identification and initial structure-activity relationships of a novel non-peptide quinolone GnRH receptor antagonist.

Screening of the Merck sample collection for non-peptide compounds with binding affinity for the rat GnRH receptor led to the identification of the substituted quinolone (1) as a lead compound in the search for a non-peptide GnRH receptor antagonist. Substantial improvements in potency (approximately 300 fold) were achieved by addition of an alkyl amine at the 4-position, a 3,5-dimethylphenyl group at the 3-position and 6-nitro-7-chloro-substitution of the 1 H-quinolone core.

Animals↗
PubMed1999

Investigation of the 4-O-alkylamine substituent of non-peptide quinolone GnRH receptor antagonists.

Synthesis and in vitro activity of the enantiomers of quinolone GnRH antagonist (+/-)-1 are reported. Chiral amino alcohols were prepared from the appropriate cyclic D- or L-amino acids by the Amdt-Eistert homologation followed by reduction of the resulting esters. Incorporation of these pharmacophores was achieved via a novel Mitsunobu alkylation of 4-hydroxyquinolones. The key amine pharmacophore for binding to the rat GnRH receptor was most active in the S-configuration. Ring size was not important for potency with 4, 5, 6, and 7-membered ring amines exhibiting similar potency.

Animals↗
PubMed1999

Metabolic flux analysis of Escherichia coli deficient in the acetate production pathway and expressing the Bacillus subtilis acetolactate synthase.

Several approaches to reduce acetate accumulation in Escherichia coli cultures have recently been reported. This reduction subsequently led to a significant enhancement in recombinant protein production. In those studies, metabolically engineered E. coli strains with reduced acetate synthesis rates were constructed through the modification of glucose uptake rate, the elimination of critical enzymes that are involved in the acetate formation pathways, and the redirection of carbon flux toward less inhibitory byproducts. In particular, it has been shown that strains carrying the Bacillus subtilis acetolactate synthase (ALS) gene not only produce less acetate but also have a higher ATP yield. Metabolic flux analysis of carbon flux distribution of the central metabolic pathways and at the pyruvate branch point revealed that this strain has the ability to channel excess pyruvate to the much less toxic compound, acetoin. The main focus of this study is the systematic analysis of the effects of small perturbations in the host's existing pathways on the redistribution of carbon fluxes. Specifically, a mutant with deleted acetate kinase (ACK) and acetyl phosphotransferase (PTA) was constructed and studied. Results from the metabolic analysis of carbon redistribution show the ackA-pta mutation will reduce acetate level at the expense of the growth rate. In addition, in the ackA-pta deficient strain a much higher lactate formation rate with simultaneously lower formate and ethanol synthesis rates was found. Expression of the B. subtilis ALS in ackA-pta mutants further reduces acetate levels while cell density similar to that of the parent strain is attained.

Acetates↗
PubMed1999

Redistribution of metabolic fluxes in Escherichia coli with fermentative lactate dehydrogenase overexpression and deletion.

Under anaerobic conditions, competition for pyruvate between the branch point enzymes pyruvate formate lyase (PFL, Km = 2 mM) and fermentative lactate dehydrogenase (LDH, Km = 7.2 mM) determines the partition of carbon flux. Two Escherichia coli mutant strains, one deficient in ackA, pta, and ldhA and the other overexpressing LDH, were constructed to systematically analyze the effects of these perturbations in the existing pathways on the redistribution of carbon fluxes. Deletion of the lactate and acetate synthesis pathways was detrimental to cell growth. Carbon flux is forced through ethanol and formate production pathways, resulting in a concomitant increase in those fluxes. In addition, overexpression of LDH simultaneously increases the common flux as well as the flux to the competing acetyl-CoA branch. Overexpression of lactate dehydrogenase (ldhA) in the parent strain increases the lactate synthesis rate from 0.19 to 0.40 mmol/g-biomass-h when the LDH activities increases from 1.3 to 15.3 units. Even an increase of more than 10 times in the LDH activity fails to divert a large fraction of the carbon flux to lactate; the majority of the flux still channels through the acetyl-CoA branch. Overexpression of LDH in the parent strain simultaneously increases the common flux as well as the flux through the acetyl-CoA branch. Subsequently, the flux amplification factors (or deviation indices which can be related to the flux control coefficients) are positive for all three fluxes occurring at the pyruvate node.

Acetyltransferases↗
PubMed1993

[Scanning electron microscopic study on the influence of monoclonal antibody on the invasion of macrophage by Leishmania parasites].

The interaction of promastigotes of Leishmania with mouse peritoneal macrophage in vitro was studied by scanning electron microscopy. The results showed that when promastigotes had been incubated with 1/1,000 McAb for 1 h, morphological changes could be seen in most promastigotes, some promastigotes were lysed and some promastigotes although adhered to the macrophage, but no penetration could be seen. When 1/1,000 McAb had been inactivated at 56 degrees C for 1 h and then incubated with promastigotes, scanning electron microscopic examination showed the promastigotes closely adhered to the surface of macrophage with their anterior end "buried" within macrophage. The results of the present study suggested that the mechanism of promastigote-macrophage adhesion was ligand-receptor binding interaction (Figs. 1-11).

Animals↗
PubMed1991

[Application of monoclonal antibodies against Leishmania donovani, II. Detection of circulating antigen in sera of visceral leishmaniasis before and after treatment].

Monoclonal antibodies L12F7 against the target antigen of L. donovani promastigotes were used for the detection of circulating antigen (CAg) from sera of visceral leishmaniasis patients. The results showed that of 118 serum samples from visceral leishmaniasis tested, 105 were positive (88.9%). 55 normal serum samples were negative. No cross reaction with sera from patients with vivax malaria, schistosomiasis, leprosy and brucellosis, was found. The authors suggested that this assay may be used as a sensitive and new serodiagnostic test for detecting existing infection of visceral leishmaniasis for epidemiological survey and for assessment of cure after effective treatment.

Animals↗
PubMed1989

Feeding pure docosahexaenoate or arachidonate decreases plasma triacylglycerol secretion in rats.

Essential fatty acid (EFA)-deficient rats were fed highly purified methyl esters of docosahexaenoate (22:6n-3), arachidonate (20:4n-6), alpha-linolenate (18:3n-3) or oleate (18:1n-9) (100 mg/day, tube fed for 3-10 days), and their plasma triacylglycerol (TG) secretion rates were measured. Secretion rates of TG into plasma were reduced by tube-feeding 22:6n-3, 20:4n-6, 18:3n-3, but not 18:1n-9, to EFA-deficient rats. A significant reduction occurred after feeding 22:6n-3 for only three days. Feeding 22:6n-3 or 18:3n-3 to EFA-deficient rats for three days also reduced the activities of liver lipogenic enzymes and sharply increased the proportions of 22:6n-3 and 20:5n-3 in liver phospholipid fractions. Mechanisms by which these EFA may reduce lipogenesis are discussed.

ATP Citrate (pro-S)-Lyase↗
PubMed1985

The opioid octapeptide Met5-enkephalin-Arg6-Gly7-Leu8: characterization and distribution in rat spinal cord.

The regional quantitation, immunohistochemical localization and molecular heterogeneity of Met5-enkephalin-Arg6-Gly7-Leu8 were examined in rat spinal cord with a specific radioimmunoassay. A rostrocaudal gradient in Met5-enkephalin-Arg6-Gly7-Leu8 content was observed; the highest levels occurred in sacral cord. Dorsal cord content was higher than that of ventral cord at all spinal segments. Immunohistochemical staining supported and refined the latter observation: a dense network of perikarya and fibers was found in Laminae I and II of the dorsal horn. Cell bodies were frequently observed in lamina IV. Additional terminals were seen around the central canal and in the ventral gray matter, often outlining perikarya of motor neurons. Total Met5-enkephalin-Arg6-Gly7-Leu8 immunoreactivity could be fractionated into two main components using gel filtration chromatography. Nearly half of the total immuno-reactivity eluted as a high molecular weight peptide; the other half which co-eluted with Met5-enkephalin-Arg6-Gly7-Leu8 was further identified to be authentic Met5-enkephalin-Arg6-Gly7-Leu8 on reverse phase high pressure liquid chromatography. The present data, in conjunction with our previous study of Met5-enkephalin and Met5-enkephalin-Arg6-Phe7 indicates that all opioid peptides derived from preproenkephalin A are present in spinal cord and most likely are stored in the same neurons. Immunohistochemical localization of Met5-enkephalin-Arg6-Gly7-Leu8 in dorsal and ventral cord suggest a role for this peptide in both sensory and motor integration.

Animals↗
PubMed1982

Lactate metabolism and cytosolic NADH reducing equivalents in ovine adipocytes.

1. Isolated ovine adipocytes, unlike rat adipose tissue, could utilize lactate at a high rate. 2. When the rate of fatty acid synthesis was attenuated with 5-(tetradecyloxy)-2-furoic acid, a fatty acid synthesis inhibitor, there was a good positive correlation between the rates of lactate oxidation to CO2 and lactate incorporation into fatty acids. 3. Addition of 2,4-dinitrophenol enhanced lactate oxidation to CO2 independent of fatty acid synthesis. Under this condition, estimated cytosolic NADH formation from lactate dehydrogenation exceeded the need of NADH for cytosolic oxaloacetate reduction and for glyceride glycerol formation. 4. Mitochondria isolated from ovine adipocytes oxidized added NADH rapidly in a reconstituted alpha-glycerophosphate shuttle system. 5. It is possible that the ability of ovine adipocytes to utilize lactate may be related to the active alpha-glycerophosphate shuttle for cytosolic NADH reoxidation.

2,4-Dinitrophenol↗
PubMed1982

Glucose metabolism and effect of acetate in ovine adipocytes.

Isolated ovine adipocytes were incubated in vitro with specifically labeled 14C-glucose in the presence or absence of acetate. The flux patterns of glucose carbon through major metabolic pathways were estimated. When glucose was added as the sole substrate, approximately equal portions of glucose carbon (10%) were oxidized to CO2 in the pentose phosphate pathway, in the pyruvate dehydrogenase reaction and in the citrate cycle. Fifteen percent of the glucose carbon was incorporated into fatty acids and 43% was released as lactate and pyruvate. Addition of acetate to the medium increased glucose carbon uptake by 1.5-fold. Most of this increase was accounted for by a sevenfold increase in the activity of the pentose phosphate pathway. Acetate increased glucose carbon fluxes via pentose phosphate pathway to triose phosphates, from triose phosphate to pyruvate, into glyceride glycerol, into lactate and pyruvate and into pyruvate dehydrogenase and citrate cycle CO2. Glucose carbon incorporated into fatty acids was decreased 50% by acetate while, carbon fluxes through the phosphofructokinase-aldolase reactions were not significantly increased. Results of this study suggest that, when glucose is the sole substrate, the conversion of glucose to fatty acids in ovine adipocytes may not be limited by the maximum capacity of hexokinase, the pentose phosphate pathway or enzymes involved in the conversion of triose phosphates to pyruvate and of pyruvate to fatty acid. Acetate increased glucose utilization apparently by increasing activity of the pentose phosphate pathway as a result of enhanced NADPH utilization for fatty acid synthesis.

Acetates↗