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Y Tang

Publications and source records attributed to Y Tang.

At least 19 recordsLinked to original sources
PubMed1992

Chiral separation of nipecotic acid amides.

1-Decyl-3-(N,N-diethylcarbamoyl)piperidine (1) and alpha,alpha'-bis[3-(N-benzyl-N-methylcarbamoyl)piperidinol]-p-xyle ne (2) represent mono-N-substituted and bis-N-substituted carbamoylpiperidines, or nipecotic acid amides, respectively. Initially, several attempts were made to resolve these compounds using beta-cyclodextrin, cellulose carbamate and Pirkle-type columns. However, the interactions of the stereoisomers of the two compounds with these stationary phases did not differ enough to permit satisfactory separations. Baseline resolution was achieved using an alpha 1-acid glycoprotein (AGP) chiral column. The mobile phase was phosphate buffer (pH 7.0). Tetrabutylammonium (TBA) was used as the cationic modifier and ethanol as the uncharged modifier. Circular dichroism was used to identify the enantiomers. Compound 1 was resolved into positive and negative enantiomers and 2 into positive and negative enantiomers and a meso diastereomer. The influence of pH, buffer ionic strength, cationic and uncharged modifier concentrations on retention, chiral selectivity and resolution were evaluated. Based on the results, it is suggested that both ionic and hydrophobic interactions may be responsible for retention and resolution.

Buffers↗
PubMed1992

Synthesis and cholinergic properties of N-aryl-2-[[[5-[(dimethylamino)methyl]-2-furanyl]methyl]thio]ethylamino analogs of ranitidine.

A series of N-aryl-2-[[[5-[(dimethylamino)methyl]-2- furanyl]methyl]thio]ethylamino analogs of the H2-antagonist, ranitidine, was synthesized and the abilities of the compounds to alleviate the cholinergic deficit characteristic of Alzheimer's disease evaluated. The compounds were initially tested for their ability to inhibit human erythrocyte acetylcholinesterase activity in vitro. Selected compounds were further evaluated for butyrylcholinesterase inhibition, M1 and M2 cholinergic receptor binding, potentiation of ileal contractions, and the ability to elevate brain acetylcholine levels in mice. The analogs were compared to tetrahydroaminoacridine and to a recently reported series of bis-[[(dimethylamino)methyl]furans]. The N-aryl-2-[[[5-[(dimethylamino)methyl]-2- furanyl]methyl]thio]ethylamine derivatives were generally comparable to tetrahydroaminoacridine and the bis[[(dimethylamino)methyl]furans] in acetylcholinesterase inhibition, M1/M2 receptor binding, and the potentiation of ileal contractions, while being more potent inhibitors of acetylcholinesterase than butyrylcholinesterase. The 4-nitro-3-pyridazinyl analog, 26, was notable in demonstrating a potent and selective binding to the M2 receptor, with an M2 IC50/M1 IC50 of 0.060. Compounds in which the substituents on the dinitro-N-aryl moiety were relatively small were the best at inhibiting acetylcholinesterase in vitro. The N-aryl-2-[[[5-[(dimethylamino)methyl]-2- furanyl]methyl]thio]ethylamines in general, and those with small N-aryl substituents in particular, were superior to the bis[[(dimethylamino)methyl]furans] in elevating brain ACh levels in mice, probably due to enhanced distribution into the CNS. The 1,5-difluoro-2,4-dinitrophenyl analog, 8, resulted in the largest elevation in brain acetylcholine levels, affording a 53% increase at 88 mg/kg.

Acetylcholine↗
PubMed1992

Synthesis and cholinergic properties of bis[[(dimethylamino)methyl]furanyl] analogues of ranitidine.

The histaminergic H2 antagonist, ranitidine, has also been found to significantly inhibit acetylcholinesterase (AChE) in vitro. In an effort to develop novel, nonquaternary AChE inhibitors capable of penetrating into the CNS and alleviating the cholinergic deficit characteristic of Alzheimer's disease, a series of bis[[(dimethylamino)methyl]furanyl] analogues of ranitidine has been synthesized. All compounds were evaluated for human erythrocyte AChE inhibitory activity and compared to ranitidine, physostigmine, and tetrahydro-9-aminoacridine (THA). The most active AChE inhibitors were N,N'-disubstituted derivatives of 2-nitro-1,1-ethenediamine and 4,6-dinitro-1,3-benzenediamine, with compound 8 demonstrating activity greater than physostigmine. Deletion of the diaminonitroethene group in a series of alkyl and aryl bis-thioethers, yielded a number of slightly less active compounds, comparable in potency to THA. The 13 most active AChE inhibitors all demonstrated a more selective inhibition of AChE, as opposed to butyrylcholinesterase inhibition, than did THA. Compounds 3 and 22 were equally active to THA in potentiating rat ileal contractions. Binding studies demonstrated M1 and M2 cholinergic receptor affinities slightly greater than or equal to THA. Differential receptor binding studies showed compound 12 resembled THA in agonist/antagonist activity. Compounds 11-13 significantly elevated mouse brain acetylcholine levels, when administered at 80% of their approximate lethal doses, but were less active than THA or physostigmine.

Animals↗
PubMed1992

Amino acid sequencing of a trypsin inhibitor by refined 1.6 A X-ray crystal structure of its complex with porcine beta-trypsin.

The stoichiometric complex formed between porcine beta-trypsin and the Momordica charantia, Linn. Cucurbitaceae trypsin inhibitor-A (MCTI-A) was crystallized and its X-ray crystal structure determined using molecular replacement method. The primary sequence and topology of the inhibitor was determined by recognizing the electron density and refined to a final R value of 0.167 (7.0-1.6 A) with RMS deviation of bond lengths from standard values 0.012 A. The sequence was compared with those obtained by other groups and was found to be similar to the squash proteinase inhibitor. Its spatial structure and the conformation of its primary binding segment from Cys-3I (P3) to Glu-7I (P3') which contains the reactive scissile bond Arg-5I C-Ile-6I N were also very similar with other squash family proteinase inhibitors.

Amino Acid Sequence↗
PubMed1992

Protective effect of anisodamine on cultured bovine pulmonary endothelial cell injury induced by oxygen-free radicals.

Anisodamine, a Chinese traditional medicine herb, has been used for treatment of adult respiratory distress syndrome effectively, but little is known about its mechanism. We attempted to investigate if anisodamine could protect bovine pulmonary endothelial cell injury induced by exogenous oxygen-free radicals that were generated by xanthine/xanthine oxidase or opsonized zymosan-stimulated polymorphonuclear leukocytes. Results showed that with the addition of xanthine/xanthine oxidase into cultured bovine pulmonary endothelial cells, production of malondialdehyde and release of lactate dehydrogenase in supernatant increased, and synthesis of prostacyclin decreased. Damaged cellular membranes were revealed by scanning electron microscopy. The same was true for the addition of opsonized zymosan-stimulated polymorphonuclear leukocytes. While treatment with anisodamine greatly attenuated all of the above-mentioned parameters, results showed that (1) cultured bovine pulmonary endothelial cells could be damaged by oxygen-free radicals, (2) anisodamine had a protective effect on this injury as effective as that of superoxide dismutase and catalase, and (3) the membrane-stable action might contribute to the mechanism of protective effect against this injury.

6-Ketoprostaglandin F1 alpha↗
PubMed1992

Building protein backbones from C alpha coordinates.

An automatic procedure for building polyalanine backbones from guiding alpha-carbon positions is presented. Polyalanine backbones are built based on the geometric restraints of angle N-C alpha-C and the knowledge of main-chain dihedral angle distributions. A building module constructs a list of polyalanine backbones that follow exactly the C alpha trace. Then a selection module selects one backbone with the largest portion of phi-psi pairs in favoured regions. Several test cases on C alpha coordinates from X-ray refined structures give acceptable results. Less than 10% of the peptide planes are incorrectly built, and the result is not sensitive to random shift up to 0.5 A of C alpha coordinates.

Amino Acid Sequence↗
PubMed1992

The synthesis of the aortic valve closure sound of the dog by the mean filter of forward and backward predictor.

The application of a new algorithm, the mean filter of forward and backward predictor, to synthesize the aortic component of the second heart sound (A2), according to an exponentially damped sinusoid model, is described. The resulting estimates of four modeling parameters composing each sinusoid of A2 (amplitude, damping factor, frequency, and phase) were used to synthesize the original aortic sounds. The synthesized sounds were then compared to the original sounds recorded on the thorax of six dogs and an error index was computed. The results show that the method is more precise than the forward predictor filter, the backward predictor filter, and the improved KT algorithm. The new algorithm is also highly stable and the error index between the original A2 and the synthesized waveforms is always less than 1%.

Algorithms↗
PubMed1992

[Alteration in resistance of Plasmodium falciparum to chloroquine after cessation of chloroquine medication for twelve years].

In view of the fact the resistance of Plasmodium falciparum to chloroquine occurred extensively in Hainan, a decision was made in 1979 that the use of chloroquine should be quit in the whole province. A longitudinal survey on chloroquine-sensitivity of P. falciparum was carried out during 1981-1991 to observe the variation in resistance of the parasite after the cessation of the chloroquine medication for every 2-3 years. A tendency of progressive decline of resistance was revealed. By using in vitro test, the rate of chloroquine-resistant P. falciparum dropped from 97.9% in 1981 to 60.9% in 1991 (P < 0.001). The mean dosage of chloroquine for complete inhibition of schizont formation declined from 10.46 pmol/microliters in 1981 to 3.02 pmol/microliters in 1991 (P < 0.001). The percentage of population requiring larger dosage (6.4 pmol/microliters to completely inhibit schizont formation declined from 83.3% in 1981 to 17.4% in 1991 (P < 0.001); whereas those requiring small dosage (1.6 pmol/microliters), increased from 4.2% in 1981 to 60.8% in 1991 (P < 0.001). In in vivo test, the rate of chloroquine-resistant P. falciparum decreased from 84.2% in 1981 to 40% in 1991 (P < 0.001). The proportion of RII plus RIII cases of the total resistant cases dropped from 59.4% in 1981 to 37.5% in 1991 (0.02 > P > 0.01).

Animals↗
PubMed1991

In vivo catalysis of a metabolically essential reaction by an antibody.

We have established a growth selection requirement for a catalytic antibody with modest chorismate mutase activity. Conversion of (-)-chorismate into prephenate is the key step in the biosynthesis of the aromatic amino acids tyrosine and phenylalanine. Strains of the yeast Saccharomyces cerevisiae containing an insertion mutation in the structural gene for the enzyme chorismate mutase (EC 5.4.99.5) require exogenous supplements of these two amino acids for efficient growth. Intracellular expression of the heterologous antibody catalyst in one such strain, identified by random mutagenesis and genetic selection, provides a substantial growth advantage under auxotrophic conditions; complementation was not observed with an unrelated esterolytic antibody. In addition to demonstrating that tailored immunoglobulin catalysts can carry out vital biochemical reactions in vivo, these experiments provide a powerful selection assay for identifying genetic changes within the antibody molecule itself that augment chemical efficiency.

Antibodies↗
PubMed1991

Purification and characterisation of the TnsB protein of Tn7: a transposition protein that binds to the ends of Tn7.

Tn7, a large bacterial transposon encodes 5 proteins required for its transposition. We report a rapid and easy purification of one of these proteins, TnsB, from an overexpression strain. This protein was shown to bind to the ends of Tn7, in a bandshift assay, in two distinct stages as a function of protein concentration. DNasel footprinting at each end of Tn7 showed that the TnsB recognition sequence, a set of 22 bp repeats, plus Tn7 termini are protected. Binding of TnsB appeared cooperative but was only observed above a threshold concentration of protein. ATP and Mg2+ had no effect on the pattern of protection, nor did addition of other Tn7-encoded proteins. Hydroxyl radical footprinting, performed at the right end, showed that TnsB binds preferentially to one side of the DNA helix.

Bacterial Proteins↗
PubMed1991

Yeast expression of a catalytic antibody with chorismate mutase activity.

The catalytic antibody 1F7 promotes the rearrangement of chorismate into prephenate. We cloned and sequenced the genes encoding this catalyst to determine the origin of the observed rates and specificity. The antibody cDNAs were modified and inserted into inducible expression vectors. Simultaneous intracellular expression of the light and truncated heavy chains in strains of the yeast Saccharomyces cerevisiae lacking natural chorismate mutase resulted in the production of properly folded and assembled Fab antibody. Assembly of the light and heavy immunoglobulin chains is roughly 60-70% efficient in our in vivo system, lagging behind light chain synthesis throughout log and stationary phase. Nevertheless, high intracellular levels of functional Fab antibody (0.1% of total cellular protein) were obtained with an ultra-high copy number plasmid. As yeast-derived 1F7(Fab) catalyzes the chorismate mutase reaction with the same specific activity as antibody isolated from the hybridoma, our expression system now makes possible the application of classical and "reverse" genetics to the study and improvement of this first-generation abzyme.

Amino Acid Sequence↗
PubMed1991

Determination of the enantiomeric purity of scopolamine isolated from plant extract using achiral/chiral coupled column chromatography.

The optical purity of scopolamine derived from Datura sanguinea was determined using coupled column chromatography. A C18 column was used to separate scopolamine from the additional alkaloids and other biological material present in the vegetal extract. The C18 column was coupled through a six-port switching valve to two beta-cyclodextrin columns in series which were used to resolve the scopolamine enantiomers. A single acetylated beta-cyclodextrin column gives equivalent results to the native cyclodextrin columns because of slightly higher enantioselectivity for scopolamine. A multistep extraction procedure is used to isolate scopolamine from the vegetal material. 4-6% of the scopolamine in the final extract was found to be the d enantiomer. Sample extracts as well as commercial scopolamine hydrobromide were treated under various conditions commonly encountered during typical commercial extraction procedures and analyzed in order to determine if the d enantiomer was present in the original material or if it was produced during the extraction process and, if so, determine which step and conditions contribute to racemization. Both the salt and the extract were found to be susceptible to racemization under basic conditions (greater than or equal to pH 9) although the extract appeared to be more susceptible than the salt. Tropic acid formed from the hydrolysis of scopolamine seemed to be completely racemized even though the remaining scopolamine was only partially racemized. Within experimental error, no d enantiomer was found in the original fresh plant material.

Acetylation↗
PubMed1991

[Proliferation of Reed-Sternberg cells in 5 Hodgkin's cell lines].

Using the monoclonal antibody Ki-67 that detects a cell proliferation-associated human nuclear antigen, incorporations of bromodeoxyuridine (Brud) and 3H-Thymidine, we studied the proliferative capacity of Reed-Sternberg (RS) cells in Hodgkin's cell lines L428, KM-H2, Holden, L540 and L591. The results revealed that in all cell lines, except L591, more than 55% of RS cells were found positive for Ki-67, and over 50% of them had Brud incorporation 5 days after cultivation. The positive score for 3H-Thymidine incorporation was low, and it is assumed that the time taken for 3H-Thymidine in cultivation was short. It shows that at least half of RS cells in these cell lines have proliferation-associated nuclear antigen or can synthesize DNA, and so they are proliferative.

Antibodies, Monoclonal↗
PubMed1991

[Observation of enzyme histochemistry and ultrastructure of brain in kindling rats with epilepsy induced by intraperitoneal injection of coriaria lactone].

Kindling model of epilepsy induced by intraperitoneal injection of Coriaria lactone (CL) was used in the experiment. The dose of CL was 1.25 mg/kg. Thirty rats in various periods of kindling were killed and the materials of cerebral cortex, hippocampus and cerebellum were drawn. The enzyme activities of AchE, NADHD, CCO, LDH, SDH, AcP, ANAE and AkP of these areas were observed with enzyme histochemical techniques. In another three kindled rats, two blank control rats and two NS control rats, the ultrastructure of neurons in hippocampus were observed. The results of experiments showed an increased activity of enzymes related to saccharometabolism and energy metabolism, indicating that the metabolism of brain in rats was increased by repeated kindling seizures. The mechanism of kindling seizure induced by CL may be related to inhibitory effect of CL on AchE activity of brain. The degeneration damage of brain neurons in kindled rats may result from using CL for a long time.

Acetylcholinesterase↗
PubMed1991

The identification of female sandflies of the subgenus Larroussius by the morphology of the spermathecal ducts.

The complete spermathecae of 13 species of Larroussius were dissected and examined. The base of the duct of 4 species (aculeatus, guggisbergi, tobbi, wui) is bell-shaped: they are easily distinguished by differences in shape. Five other species (perniciosus, pedifer, longicuspis, perfiliewi, galilaeus) have lateral structures at the base of the duct: slight differences between perniciosus, pedifer and longicuspis distinguish these species: the structures of perfiliewi and galilaeus are the same. Species of a third group (neglectus, syriacus) have a common duct with no lateral structures: they are distinguishable by minor differences. Two species (ariasi, orientalis) from a fourth group with expanded distal parts of the duct; the size and shape of the expanded parts easily separates the species. The study shows a great variation in the morphology of the base of the spermathecal ducts of Larroussius and confirms the value of this feature in identifying otherwise indistinguishable females of the subgenus.

Animals↗