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At least 1,171 records · Page 65Linked to original sources
PubMed1992

Partial characterization and detergent solubilization of the putative glutathione chemoreceptor from hydra.

Feeding behavior in hydra is initiated by the association of glutathione (GSH) with a putative external chemoreceptor. In the present study, the binding of [35S]GSH to hydra membranes has been characterized. Nondisplaceable [35S]GSH binding which compromised previous analyses [Grosvenor, W., Bellis, S., Kass-Simon, G., & Rhoads, D. (1992) Biochim. Biophys. Acta (in press)] was eliminated by treating membranes with an inhibitor of GSH metabolism, borate in combination with L-serine. The specific binding which was not inhibited by borate/serine demonstrated many of the characteristics expected of a ligand/receptor interaction. The binding was rapid, reversible, and saturable. A Scatchard analysis of saturation isotherms indicated a dissociation constant (KD) of 3.4 microM, a value which is in good agreement with concentrations of glutathione which are known to induce feeding behavior. Hydra membranes were detergent-solubilized with 10 mM 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS), 100 mM KCl, and 10% glycerol. The soluble fraction contained 40% of the original saturable, reversible GSH binding activity. The KD for GSH binding to the solubilized preparation was estimated as 2.7 microM, a valuable which is not appreciably different from the KD for binding to intact membranes. The fidelity of GSH binding in the solubilized preparation suggests that this preparation will be useful in further characterization of the putative glutathione chemoreceptor.

Animals↗
PubMed2002

Formation of a trypsin-borate-4-aminobutanol ternary complex.

The formation of ternary complexes involving serine proteases, borate, and an alcohol has important implications for understanding the physiological actions of borate and for the development of tight binding inhibitors for this class of enzymes. Recent studies of a related enzyme, gamma-glutamyl transpeptidase, which is subject to inhibition by a labile serine/borate mixture, have demonstrated that construction of a non-labile boronate analogue results in an inhibitor with nearly 10(5)-fold greater potency. To evaluate the generalization of this biochemistry to serine proteases, we have observed the ternary complex formed from 4-aminobutanol, borate, and trypsin. A combination of (11)B and (1)H NMR and spectrophotometric assays using acetylarginine p-nitroanilide (Ac-Arg-pNA) as the chromogenic substrate all indicate a cooperative binding interaction in which the borate is esterified by the oxygen atoms of the 4-aminobutanol and trypsin residue Ser(195). Two downfield-shifted proton resonances at 15.5 and 16.6 ppm are proposed to arise from the labile imidazolium protons on His(57), indicating a salt bridge interaction with the negatively charged borate. A cooperativity parameter alpha of 0.2 is derived from the assays. These results provide the first direct evidence for formation of a ternary complex involving a serine protease, borate, and an alcohol, and suggest that this represents a general approach for the development of tight binding ligands.

Amino Alcohols↗
PubMed2006

Catalyzed decomposition of urea. Molecular dynamics simulations of the binding of urea to urease.

We present the results of molecular dynamics simulations on the urea/urease system. The starting structure was prepared from the 2.0 A crystal structure of Benini et al. [(1999) Struct. Folding Des. 7, 205-216] of DAP-inhibited urease (PDB code ), and the trimeric structure (2479 residues) resulted in 180K atoms after solvation by water. The force field parameters were derived using the bonded model approach described by Hoops et al. [(1991) J. Am. Chem. Soc. 113, 8262-8270]. Three different systems were analyzed, each one modeling a different protonation pattern for the His320 and His219 residues. In each case, the three monomers of urease have been analyzed separately. The time-averaged structures observed in the three monomers suggest that urease could follow two different competitive mechanisms. A "protein-assisted proton transfer" mechanism points to Asp221 as crucial for catalysis. An "Asp-mediated proton transfer" involves the transfer of a proton from the bridging OH to an NH2 moiety of urea, assisted by Asp360 in the active site. The impact of the simulation results on our understanding of urease catalysis is discussed in detail.

Bacillus↗
PubMed1996

Dityrosine formation in calmodulin: cross-linking and polymerization catalyzed by Arthromyces peroxidase.

We employ bovine brain calmodulin, a protein that is subject to photoactivated dityrosine formation [Malencik, D. A., & Anderson, S. R. (1987) Biochemistry 26, 695; (1994) Biochemistry 33, 13363], as a model for the development of an efficient enzyme-catalyzed protein cross-linking technique. Key steps in the elaboration of the procedure are (1) identification of a peroxidase, from Arthromyces ramosus, that catalyzes dityrosine production in proteins that are not acted on by other common peroxidases, (2) monitoring of the intrinsic fluorescence of dityrosine to determine optimum reaction conditions, achieved with calmodulin in solutions containing boric acid-sodium borate (concentration > or = 0.2 M), approximately pH 8.3, approximately 40 degrees C, and (3) quenching of the reaction with reduced glutathione. Arthromyces peroxidase is the only common peroxidase able to catalyze significant dityrosine production in calmodulin, through a reaction that is largely intermolecular. Gel filtration yields fractions (accounting for approximately 40% of the initial calmodulin) that represent differing mobility ranges in NaDodSO4 polyacrylamide gel electrophoresis and contain close to the maximum possible amounts of dityrosine. The various fractions undergo Ca2+-dependent conformational changes detected in sedimentation velocity and/or fluorescence anisotropy measurements. Most of the samples stimulate the Ca2+-dependent activity of smooth muscle myosin light chain kinase. In catalytic assays utilizing the synthetic phosphatic acceptor peptide, the average activities range from 50 to 100% of that determined for native calmodulin. However, only the least polymerized fraction and the photogenerated calmodulin dimers significantly enhance the p-nitrophenylphosphatase activity of calcineurin. The ability to prepare soluble calmodulin polymers that retain a substantial degree of biological activity and exhibit the intense visible fluorescence of dityrosine illustrates the potential usefulness of Arthromyces peroxidase in the zero-length cross-linking of proteins.

Animals↗
PubMed2004

Reaction properties of the trans-hyponitrite complex [Ru2(CO)4(mu-H)(mu-PBu(t)2)(mu-Ph2PCH2PPh2)(mu-eta2-ONNO)].

The protonation of [Ru(2)(CO)(4)(mu-H)(mu-PBu(t)()(2))(mu-dppm)(mu-eta(2)-ONNO)] (1) with HBF(4) occurs at the oxygen of the noncoordinating side of the trans-hyponitrite ligand to give [Ru(2)(CO)(4)(mu-H)(mu-PBu(t)()(2))(mu-dppm)(mu-eta(2)-ONNOH)][BF(4)] (2) in good yield. The monoprotonated hyponitrite in 2 is deprotonated easily by strong bases to regenerate 1. Furthermore, 1 reacts with the methylating reagent [Me(3)O][BF(4)] to afford [Ru(2)(CO)(4)(mu-H)(mu-PBu(t)()(2))(mu-dppm)(mu-eta(2)-ONNOMe)][BF(4)] (3). The molecular structures of 2 and 3 have been determined crystallographically, and the structure of 2 is discussed with the results of the DFT/B3LYP calculations on the model complex [Ru(2)(CO)(4)(mu-H)(mu-PH(2))(mu-H(2)PCH(2)PH(2))(mu-eta(2)-ONNOH)](+) (2a). Moreover, the thermolysis of 2 in ethanol affords [Ru(2)(CO)(4)(mu-H)(mu-OH)(mu-PBu(t)()(2))(mu-dppm)][BF(4)] (4) in high yield, and the deprotonation of 4 by DBU in THF yields the novel complex [Ru(2)(CO)(4)(mu-OH)(mu-PBu(t)()(2))(mu-dppm)] (5).

Borates↗
PubMed2003

Influence of the extracting solvent upon the structural properties of Amaranth (Amaranthus hypochondriacus) glutelin.

Two amaranth glutelin preparations, Gt-bo extracted with borate buffer at pH 10 and Gt-na extracted with 0.1 N NaOH, were characterized and compared with the amaranth polymerized 11S globulin (Gp, globulin-P). Gt-bo and Gt-na presented very similar polypeptidic composition and a similar reactivity against an anti-Gp polyclonal antibody, although lower than that of Gp. It is demonstrated that Gt-na is composed of denatured and dissociated molecules, whereas Gt-bo consists of folded molecules. The size, polypeptidic composition, thermal stability, and denaturation enthalpy of Gt-bo molecules were similar to those of Gp subjected to a borate treatment at pH 10. The Gp immunoreactivity decreased to the level of Gt reactivity when subjected to alkaline treatment; this could be due to conformational changes. Results suggest that, like Gp, amaranth Gt molecules may be hexameric oligomers of approximately 300 kDa. They would be partially unfolded during the alkaline extraction.

Amaranthus↗
PubMed2005

Asymmetric total synthesis of dibenzocyclooctadiene lignan natural products.

[structure: see text] Full details of the asymmetric total syntheses of the dibenzocyclooctadiene lignans interiotherin A, angeloylgomisin R, gomisin O, and gomisin E (epigomisin O) are presented. The syntheses were based on a unified synthetic strategy involving a novel crotylation using the Leighton auxiliary that occurred with excellent asymmetric induction (>98:2 enantiomeric ratio), a diastereoselective hydroboration/Suzuki-Miyaura coupling reaction sequence, and an atropdiastereoselective biarylcuprate coupling, both of which occurred with total (>20:1) stereocontrol. The syntheses were achieved in six to eight steps from simple aromatic precursors.

Aldehydes↗
PubMed2006

Silica-coated CdTe quantum dots functionalized with thiols for bioconjugation to IgG proteins.

Quantum dots (QDs) have been increasingly used in biolabeling recently as their advantages over molecular fluorophores have become clear. For bioapplications QDs must be water-soluble and buffer stable, making their synthesis challenging and time-consuming. A simple aqueous synthesis of silica-capped, highly fluorescent CdTe quantum dots has been developed. CdTe QDs are advantageous as the emission can be tuned to the near-infrared where tissue absorption is at a minimum, while the silica shell can prevent the leakage of toxic Cd(2+) and provide a surface for easy conjugation to biomolecules such as proteins. The presence of a silica shell of 2-5 nm in thickness has been confirmed by transmission electron microscopy and atomic force microscopy measurements. Photoluminescence studies show that the silica shell results in greatly increased photostability in Tris-borate-ethylenediaminetetraacetate and phosphate-buffered saline buffers. To further improve their biocompatibility, the silica-capped QDs have been functionalized with poly(ethylene glycol) and thiol-terminated biolinkers. Through the use of these linkers, antibody proteins were successfully conjugated as confirmed by agarose gel electrophoresis. Streptavidin-maleimide and biotinylated polystyrene microbeads confirmed the bioactivity and conjugation specificity of the thiolated QDs. These functionalized, silica-capped QDs are ideal labels, easily synthesized, robust, safe, and readily conjugated to biomolecules while maintaining bioactivity. They are potentially useful for a number of applications in biolabeling and imaging.

Biotinylation↗
PubMed2003

An NMR and X-ray study of the structure of the azo coupling product of 4-dimethylaminopent-3-en-2-one and benzenediazonium-tetrafluoroborate.

4-Dimethylaminopent-3-en-2-one reacts with two molecules of benzenediazonium-tetrafluoroborate to give compound 1. The structure of this compound was determined by means of X-ray analysis of its crystal and 1H, 13C and 15N NMR spectra of its solution in CDCl3. The molecule of this compound contains one azo group and one hydrazone group. The substance exists, both in crystal form and in solutions of concentrations above 0.1 mol l(-1), in the form of a dimer, in which the pair of molecules are bound by two hydrogen bonds N-H...N. On diluting the solution, the dimers decompose, the two forms being in an equilibrium that is rapid on the NMR time scale.

Borates↗
PubMed1995

Enamel surfaces after orthodontic bracket debonding.

The enamel surfaces of extracted teeth were studied clinically and with a scanning electron microscope following debonding of orthodontic attachments and subsequent polishing. Excess orthodontic resin was removed with tungsten carbide burs and abrasive discs. Several combinations of polishing agents were evaluated. The no. 30 fluted tungsten carbide bur appeared to be the most efficient method of removing highly filled resin, and it produced the least amount of scarring. A polishing sequence was developed which used resin points and cups followed by a water slurry of fine pumice and brown and green cups. This procedure was tested clinically and appeared to return the enamel to an acceptable condition. This procedure is fast, efficient, and comfortable for the patient.

Aluminum Oxide↗