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J T Yang

Publications and source records attributed to J T Yang.

At least 73 records · Page 4Linked to original sources
PubMed1988

Isolation and characterization of the gene encoding the heavy chain of Drosophila kinesin.

An antiserum that recognizes the heavy chain of Drosophila kinesin was used to isolate Drosophila cDNA clones. Immunoblot analysis of the proteolytic fragments of the protein produced by one of the cDNA clones has demonstrated that the cDNA clones encode the heavy chain of Drosophila kinesin. The in vitro-synthesized product of the largest cDNA comigrates with Drosophila kinesin heavy chain on NaDodSO4/polyacrylamide gels and binds to taxol-stabilized microtubules in the presence of the nonhydrolyzable analogue of ATP, 5'-adenylyl imidodiphosphate, but not in the presence of ATP or 0.1 M KCl. Analysis of the cDNA clones suggests that there is a single gene encoding kinesin heavy chain in Drosophila located at polytene chromosome position 53A. However, Southern hybridization analyses suggest the presence of related sequences in the Drosophila genome.

Animals↗
PubMed1987

Conformation similarities of the globular and tailed forms of acetylcholinesterase from Torpedo californica.

The conformation of the globular dimer (G2), the tailed asymmetric dodecamer (A12, also containing some tailed octamer A8) and the globular tetramer (G4, prepared by removing the collagen-like tail from A12) of acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7) was studied by circular dichroism (CD) in the ultraviolet region. The G2 and G4 forms had similar conformation with about 40% alpha-helix, 35% beta-sheets and 4% beta-turns; the tailed form had a lower helicity (about 34%) and beta-form (about 25%) content probably because of the presence of the tail whose CD spectrum resembles that of an unordered form, but it had about the same amount of beta-turns as the other two forms. All three forms also had similar CD spectra in the near-ultraviolet region due to their non-peptide chromophores. The pH, thermal and urea denaturation of the three acetylcholinesterase forms was also similar to each other. The pH-dependency of both the enzymatic activity and CD intensity of the three forms showed bell-shaped curves with a plateau at pH 7-8. The activity was completely lost at pH below 5 or above 10, but the corresponding CD spectra retained 70-80% of the original magnitudes. Thermal denaturation of the three forms at pH 7.5 showed a conformational transition and loss of activity between 30 and 40 degrees C, but the CD intensity of the helical band at 222 nm was reduced by only 20-30%. Urea denaturation of the three forms began at 1 M urea; it was protein concentration- and time-dependent. Again, the activity disappeared faster than the decreasing CD intensity. Thus, the overall conformation of the three acetylcholinesterase forms appears to be relatively stable, but their active site is easily perturbed by changing the environment. The loss of activity correlated well with the disappearance of the CD band of tryptophan(s) in the near-ultraviolet region, suggesting that the Trp residue(s) might be at or near the active center of the enzyme.

Acetylcholinesterase↗
PubMed1987

Interaction of snake venom cardiotoxin (a membrane-disruptive polypeptide) with human erythrocytes.

The action of 7.2 microM cardiotoxin on 0.25% human erythrocytes in a plasma extender solution was studied by the interaction of toxin with intact red blood cells and subsequent hemolysis of the cells. The binding of toxin to cells was completed within 10 min, whereas the membrane rigidity was weakened in a non-lytic period for about 25 min. The toxin molecules bound almost exclusively to the membrane. The bound toxin could not be liberated with either 0.5% Triton X-100 or 0.1 N NaOH. The degree of binding was slightly reduced in the presence of 10 mM mono- and divalent inorganic salts. The action of toxin might weaken the in situ association of several proteins that are linked with band 3 protein of the membrane, thus making the cells fragile and altering the shape of the cell to a smooth sphere.

Animals↗
PubMed1987

Conformation similarities of ricin A-chain and trichosanthin.

The conformation of ricin A-chain from castor bean was studied by circular dichroism at pH 4.7, 7 and 9 and compared with that of trichosanthin from the Chinese herb Tianhuafen. The CD spectra of ricin A-chain and trichosanthin were nearly identical at each of the three pHs. Analysis of the data indicated that, like trichosanthin, ricin A-chain had about 29% alpha-helix and 42% beta-sheet but no beta-turn. However, there was a subtle difference in the CD spectra in 20 mM sodium dodecyl sulfate, the addition of which at pH 7 slightly increased the helicity and decreased the content of beta-sheet of ricin A-chain in contrast to a larger increase in helicity at the expense of beta-sheet for trichosanthin, thus indicating a different stability against the surfactant. Native ricin A-chain and trichosanthin had about the same amount of secondary structure, which supports the belief that a high degree of sequence homology of the two proteins [Zhang & Wang (1986) Nature 321, 477-478] may lead to a conformational similarity between them, even though the two proteins are not taxonomically related.

Abortifacient Agents, Nonsteroidal↗
PubMed1986

Conformation of abortifacient proteins: trichosanthin, alpha-momorcharin and beta-momorcharin.

The conformations of three abortifacient proteins, trichosanthin from the Chinese herb Tianhuafen and alpha- and beta-momorcharin from the Chinese herb Kuguazi, were studied by circular dichroism. Their spectra in the ultraviolet region (188-250 nm) were similar to each other and also pH-independent (between pH 5 and 9). All three proteins contained about 30% helix, as compared with 39% for trichosanthin by X-ray diffraction study, and 40-60% beta-sheets, but had no beta-turns, suggesting a structural homology among the proteins. The addition of 20 mM sodium dodecyl sulfate nearly doubled the helicity of beta-momorcharin at the expense of beta-sheets but had a small effect on the conformation of alpha-momorcharin, whereas the corresponding change in conformation for trichosanthin was in between the two momorcharins. This implies a marked difference in stability of the three proteins against the surfactant.

Abortifacient Agents↗
PubMed1986

Competitive binding of dynorphin-(1-13) and beta-endorphin to cerebroside sulfate in solution.

Circular dichroism was used as a probe for competitive binding of two opioid peptides, dynorphin-(1-13) and beta-endorphin, with cerebroside sulfate, a membrane lipid thought to be part of the morphine receptor complex. The rationale was that bound beta-endorphin is partially helical but bound dynorphin-(1-13) remains unordered, thus making it possible to detect the degree of binding of beta-endorphin. The addition of dynorphin-(1-13) to a cerebroside sulfate solution of beta-endorphin invariably displaced beta-endorphin from the peptide-lipid complex, but the addition of beta-endorphin had little effect on dynorphin-(1-13) bound to the lipid. Similar results were obtained for competitive binding of the two peptides with two other amphiphiles, sodium dodecyl and decyl sulfate. The maximum number of binding sites on dynorphin-(1-13) and beta-endorphin was between five and six, which coincides with the five positively charged side chains plus an alpha NH+3 group at the NH2 terminus on both peptide molecules. The results support our working hypothesis that dynorphin-(1-13) may displace beta-endorphin bound to the receptor, which in turn can account for the inhibition of beta-endorphin-induced analgesia by dynorphin-(1-13).

Binding, Competitive↗
PubMed1984

Bis[cyclo(histidylhistidine)]copper(II) complex that mimicks the active center of superoxide dismutase has its catalytic activity.

The formation of copper complexes with bis[cyclo( histidylhistidine )] copper(II) was determined potentiometrically; the maximum coordination number was four deprotonated histidine residues per Cu(II) ion. This complex mimicks the active center of Cu/Zn superoxide dismutase (superoxide:superoxide oxidoreductase, EC 1.15.1.1). Its absorption spectrum showed a broad band above 600 nm as compared with the 670- to 680-nm band of the enzyme. Its CD spectrum had a negative 600- to 605-nm band and a more intense positive band near 780 nm. The band positions were identical with, and the intensities were higher than, those of the enzyme, but the corresponding bands had opposite signs. This can be attributed to the difference in the distorted planar structure between the complex and enzyme. The complex catalyzed the dismutation of superoxide anion; the activity was 1/10th that of the enzyme on a molar basis, but about three times that of the enzyme on a weight basis.

Binding Sites↗
PubMed1984

The formaldehyde-donating activity of N5,N10-methylene tetrahydrofolic acid in xenobiotic biotransformation.

Reaction of reproterol, (7-(3-[2-(3,5-dihydroxyphenyl)-2-hydroxyethylamino]propyl)theophyl line (I), with formaldehyde liberated in a solution of N5,N10-methylene tetrahydrofolic acid at pH 7.3 led to the formation of 7-[3-(4,6,8-trihydroxy-1,2,3,4-tetrahydroisoquinolinyl-2)propyl]th eophylline (II), but no such reaction was observed in a solution of N5-methyl tetrahydrofolic acid. Compound II was also formed by incubation of I with rat-liver subcellular fractions. The highest formaldehyde-donating activity was found in the soluble fraction but some activity was also observed with washed mitochondria and microsomes. Dimedone was transformed to methylene bisdimedone by incubation with the soluble fraction. The amount of formaldehyde liberated in the soluble fraction during a four hour incubation at 22 degrees C was 1-3.6 mumol/g of liver. Metaproterenol and terbutaline, structurally related to I, reacted with formaldehyde to yield the corresponding tetrahydro-isoquinolines. The rate of this chemical reaction for the three drugs correlated with the amount of the tetrahydroquinolines formed by incubation with the soluble fraction and in orally dosed rats.

Animals↗
PubMed1984

Study on in vivo decarboxylation of D-penicillamine in rats.

Carboxy-labeled 14C-D-penicillamine was prepared and dosed at 50 mg/kg to Sprague-Dawley rats kept in metabolism cages. The recovery of 14C in excreta, tissue and expired air was 98.4%. The 14CO2 expired amounted only to 1.5% of the 14C-dose indicating that in vivo decarboxylation of the drug in rats is not a significant metabolic pathway.

Animals↗
PubMed1984

Membrane disintegration and hemolysis of human erythrocytes by snake venom cardiotoxin (a membrane-disruptive polypeptide).

The action of 7.2 microM cardiotoxin on 0.25% (v/v) human erythrocytes in plasma extender solution was studied by osmotic fragility and hemolysis. The toxin loosened the membrane rigidity without lysis for about 25 min and then the cells hemolyzed for about 6 h at 37 degrees. The membrane was not perturbed at 15 degrees. The hemolysis of cells was optimal at 37 degrees and virtually stopped below 20 degrees. Both events could be suppressed by adding inorganic salts or toxin antibody. Once the membrane was loosened, the addition of phospholipase A2 would potentiate the disintegration of erythrocytes. In contrast, hemolysis of erythrocytes by (Lys)n lacked a non-lytic period and was temperature independent and insensitive towards salts and phospholipase A2.

Cobra Cardiotoxin Proteins↗
PubMed1983

Cooperative binding of hexadecyltrimethylammonium chloride and sodium dodecyl sulfate to cytochrome c and the resultant change in protein conformation.

The binding of hexadecyltrimethylammonium chloride (HTAC) and sodium dodecyl sulfate (SDS) to cytochrome c was determined by potentiometric titration and the corresponding changes in protein conformation by circular dichroism (CD). The binding isotherms were biphasic; about 20 surfactant cations or anions were bound to cytochrome c in the first phase. Another 30 or so HTA+ ions were bound in the second phase, which was below the critical micelle concentration of the surfactant, but the binding of dodecyl sulfate ions in the second phase increased sharply near the critical micelle concentration. The binding of both surfactants was highly cooperative and was endothermic; the data in the first phase fitted the Hill plot. The corresponding change in the secondary structure of cytochrome c was small; the CD spectra in the ultraviolet region showed a moderate increase in the helicity in HTAC solution and some changes in conformation in SDS solution. However, the CD spectra for the Soret band indicated a marked change in the local conformation around the heme.

Animals↗
PubMed1982

Lipid-induced ordered conformation of some peptide hormones and bioactive oligopeptides: predominance of helix over beta form.

The conformation of several naturally occurring peptide hormones and bioactive oligopeptides in phospholipid solutions was studied by circular dichroism. Phosphatidylcholine induced a partial helix in human gastrin I at neutral pH, but phosphatidylserine did not unless the five consecutive glutamic acid residues in gastrin were protonated. Reduced somatostatin with two lysines and substance P with one arginine and one lysine were partially helical in phosphatidylserine, but not phosphatidylcholine, solution. Both lipids induced a helical conformation in glucagon and its COOH-terminal fragment (19-29) probably because the helical segment is primarily located at the uncharged COOH terminus. Thus, polypeptides with a helix-forming potential can have the helical conformation only when the peptides carry no charge or charges opposite to those on the polar head of the lipid. Renin substrate, which has potentials for the beta form and beta turn, seemed to form a mixture of the two conformations in phosphatidylserine solution. Angiotensin I with a strong probability for the beta form adopted the beta form in phosphatidylserine solution and sleep peptide with no structure-forming potential remained unordered in lipid solutions. The helix usually predominated over the beta form in lipid solutions if the peptide has potentials for both conformations. This could account for the preponderance of helices in bacteriorhodopsin of the purple membrane, which according to its amino acid sequence would have favored the beta form.

Amino Acid Sequence↗
PubMed1982

Role of aromatic residues in the structure-function relationship of alpha-bungarotoxin.

The conformation of alpha-bungarotoxin and its cyanogen bromide cleaved and nitrated derivatives was studied by circular dichroism (CD). Native toxin contains no helices but some beta forms and possibly beta turns. Its ordered conformation is little affected when the peptide bond between Met-27 and Trp-28 is cleaved; however, the CD due to Trp-28 is abolished. The CNBr-cleaved derivative retains its immunoaffinity toward anti-toxin sera but loses its neurotoxicity toward the acetylcholine receptor. On the basis of both CD and fluorescence spectra, Trp-28 is probably stabilized by a short-range interaction with the carboxylate group of Asp-30. The ordered conformation of the toxin is also unaltered when one of the two tyrosine residues, identified as Tyr-54, is nitrated with tetranitromethane. This Tyr(NO2)-54 derivative possesses both immunoaffinity and neurotoxicity. However, the toxin is denatured and loses its activities when the other tyrosine residue, Tyr-24, is also nitrated in 6 M guanidine hydrochloride, even after the denaturant is removed. Spectrophotometric titration of the toxin indicates that Tyr-54 has a normal apparent dissociation constant (pKa = 9.7) and Tyr-24 ionizes at pH above 11.2. Both tyrosine residues are in a polar environment, but Tyr-24 is not readily accessible to reagents and is stabilized by long-range interactions, probably involving Glu-41.

Amino Acid Sequence↗