Search results for "Biophysic"
showing 10 items of 3565 documents
Eukaryotic tRNAs(Pro): primary structure of the anticodon loop; presence of 5-carbamoylmethyluridine or inosine as the first nucleoside of the antico…
1990
The modified nucleoside U*, located in the first position of the anticodon of yeast, chicken liver and bovine liver tRNA(Pro) (anticodon U*GG), has been determined by means of TLC, HPLC, ultraviolet spectrum and gas chromatography-mass spectrometry. The structure was established as 5-carbamoylmethyluridine (ncm5U). In addition, we report on the primary structures of the above-mentioned tRNAs as well as those which have the IGG anticodon. In yeast, the two tRNA(Pro) (anticodons U*GG and IGG) differ by eight nucleotides, whereas in chicken and in bovine liver, both anticodons are carried by the same 'body tRNA' with one posttranscriptional exception at position 32, where pseudouridine is asso…
A second pathway of activation of the Torpedo acetylcholine receptor channel
1991
We have studied the interaction of the reversible acetylcholine esterase inhibitor (-)physostigmine (D-eserine) with the nicotinic acetylcholine receptor (nAChR) from Torpedo marmorata electric tissue by means of ligand-induced ion flux into nAChR-rich membrane vesicles and of equilibrium binding. We find that (-) physostigmine induces cation flux (and also binds to the receptor) even in the presence of saturating concentrations of antagonists of acetylcholine, such as D-tubocurarine, alpha-bungarotoxin or antibody WF6. The direct action on the acetylcholine receptor is not affected by removal of the methylcarbamate function from the drug and thus is not due to carbamylation of the receptor…
Are there dynamical effects in enzyme catalysis? Some thoughts concerning the enzymatic chemical step.
2015
Highlights • The possible role of enzymatic reaction dynamical effects is examined. • Solution reactions usefully inform the issue of dynamical effects in enzymes. • Division into regions containing and away from the transition state is important. • Motions in passage to/from the transition state need not lead to dynamical effects. • Transition State Theory is usually a reasonable description of enzyme kinetics.
Attracted or repelled?--a matter of two neurons, one pheromone binding protein, and a chiral center.
1998
Abstract Two species of scarab beetles, the Osaka beetle (Anomala osakana) and the Japanese beetle (Popillia japonica), utilize the opposite enantiomers of japonilure, (Z)-5-(1-decenyl)oxacyclopentan-2-one, as their sex pheromones. Each species produces only one of the enantiomers that functions as its own sex pheromone and as a very strong behavioral antagonist for the other species. Using an integrated approach we tested whether the discrimination of these two opposite signals is due to selective filtering by pheromone binding proteins or whether it originates in the specificity of ligand–receptor interactions. We found that the antennae of each of these two scarab species contain only a …
Detection of Single Oxygen Molecules with Fluorescence-Labeled Hemocyanins
2005
This study introduces a method to detect individual oxygen molecules by fluorescence microscopy of single hemocyanins. These respiratory proteins from a tarantula bind oxygen with high affinity. A spectrometric signature of the oxygenated protein is transferred to an attached fluorescence label, which can be detected at the single-molecule level. This technique opens new perspectives for the development of small and sensitive oxygen sensors as well as for the investigation of cooperative oxygen binding in respiratory proteins.
Diffusion of ionic and non-ionic contrast agents in articular cartilage with increased cross-linking--contribution of steric and electrostatic effect…
2013
Abstract Objective To investigate the effect of threose-induced collagen cross-linking on diffusion of ionic and non-ionic contrast agents in articular cartilage. Design Osteochondral plugs (O=6mm) were prepared from bovine patellae and divided into two groups according to the contrast agent to be used in contrast enhanced computed tomography (CECT) imaging: (I) anionic ioxaglate and (II) non-ionic iodixanol. The groups I and II contained 7 and 6 sample pairs, respectively. One of the paired samples served as a reference while the other was treated with threose to induce collagen cross-linking. The equilibrium partitioning of the contrast agents was imaged after 24h of immersion. Fixed char…
Valence Topological Charge-Transfer Indices for Reflecting Polarity: Correction for Heteromolecules
2005
Valence topological charge-transfer (CT) indices are applied to the calculation of dipole moments mu. The mu calculated by algebraic and vector semisums of the CT indices are defined. The model is generalized for molecules with heteroatoms and corrected for sp(3)-heteromolecules. The ability of the indices for the description of the molecular charge distribution is established by comparing them with mu of the valence-isoelectronic series of cyclopentadiene, benzene and styrene. Two CT indices, mu(vec) (vector semisum of vertex-pair mu) and mu(vec)V (valence mu(vec)) are proposed. The mu(vec) behaviour is intermediate between mu(vec) and mu(experiment). The correction is produced in the corr…
Electrostatic Contribution to the Surface Pressure of Charged Monolayers Containing Polyphosphoinositides
2008
Structural and functional studies of lateral heterogeneity in biological membranes have underlined the importance of membrane organization in biological function. Most inquiries have focused on steric determinants of membrane organization, such as headgroup size and acyl-chain saturation. This manuscript reports a combination of theory and experiment that shows significant electrostatic contributions to surface pressures in monolayers of phospholipids where the charge spacing is smaller than the Bjerrum length. For molecules with steric cross sections typical of phospholipids in the cell membrane (approximately 50 A(2)), only polyphosphoinositides achieve this threshold. The most abundant s…
Investigation of Temperature-Induced Phase Transitions in DOPC and DPPC Phospholipid Bilayers Using Temperature-Controlled Scanning Force Microscopy
2004
Under physiological conditions, multicomponent biological membranes undergo structural changes which help define how the membrane functions. An understanding of biomembrane structure-function relations can be based on knowledge of the physical and chemical properties of pure phospholipid bilayers. Here, we have investigated phase transitions in dipalmitoylphosphatidylcholine (DPPC) and dioleoylphosphatidylcholine (DOPC) bilayers. We demonstrated the existence of several phase transitions in DPPC and DOPC mica-supported bilayers by both atomic force microscopy imaging and force measurements. Supported DPPC bilayers show a broad L(beta)-L(alpha) transition. In addition to the main transition …
Local control of antibody binding to hapten-presenting interfaces: Steric and electrostatic interaction
1991
The binding of labeled antibodies to hapten substituted monolayers at the air/water interface has been studied by means of fluorescence microscopy. Haptens with various spacer lengths between the epitope and a hydrocarbon chain, anchoring the molecule to the interface, have been synthesized. With DMPC,a unspecific binding has been shown to predominate over specific binding due to electrostatic interactions. At high surface pressures the bound antibody is detached because of steric interference with the lipid head groups. Due to a reduction of electrostatic interactions, no unspecific binding is observed to monolayers of cholesterol, which carries a small dipole moment. Mixed monolayers of c…