Search PubMed⌕ Search

Biomedical subjects

D W Urry

Publications and source records attributed to D W Urry.

At least 73 records · Page 4Linked to original sources
PubMed1987

Solvent determined conformation of gramicidin affects the ability of the peptide to induce hexagonal HII phase formation in dioleoylphosphatidylcholine model membranes.

It is shown by 31P-NMR and small angle X-ray scattering that induction of an hexagonal HII phase in dioleoylphosphatidylcholine model membranes by external addition of gramicidin A' depends on the solvent which is used to solubilize the peptide. Addition of gramicidin from dimethylsulfoxide or trifluoroethanol solution leads to HII phase formation whereas addition of the peptide from ethanol does not. This solvent dependence is shown by circular dichroism to be correlated with the peptide conformation. The channel conformation appears to be responsible for HII phase formation by gramicidin.

Chemical Phenomena↗
PubMed1987

On the mechanism of channel-length dependence of gramicidin single-channel conductance.

Single-channel conductance data on four different gramicidin channel lengths demonstrate that conductance magnitude is neither inversely dependent on the square of the channel length nor on the image force arising from differences in the extent of lipid dimpling (Jordan and Vayl (1985) Biochim. Biophys. Acta 818, 416-420). Rather the conductance differences are consistent with the decreased off-rate constant for the singly occupied state as the ionic radius decreases from that of cesium ion to sodium ion coupled with the decreased probability of the doubly occupied channel due to increased ion-ion repulsion as the channel is shortened (Urry et al. (1984) Biochim. Biophys. Acta 774, 115-119).

Cesium↗
PubMed1987

Cell attachment and chemotaxis can utilize the same peptide sequence of fibronectin.

Fibronectin and fragments of the parent molecule are involved in cell-substrate attachment, cell migration and chemotaxis. The cell attachment sequence, Gly-Arg-Gly-Asp-Ser-Pro, was synthesized and tested for its ability to effect ligamentum nuchae fibroblast chemotaxis. This hexapeptide and fibronectin itself both caused directed cell migration, with maximal activity in the 10(-10) to 10(-9) M range. These data demonstrate that the fibronectin cell binding site and chemotaxis site share a common sequence.

Animals↗
PubMed1987

Open channel noise. III. High-resolution recordings show rapid current fluctuations in gramicidin A and four chemical analogues.

Using a technique for high-resolution recording of currents from lipid bilayers, we have measured the current fluctuations in open channels formed by gramicidin A (GA) and the four analogues L-Ala7-GA, L-Leu5-GA, con D-Leu5a-L-Ala5b-GA and, des-L-Val7-D-Val8-GA. Over the frequency range 40 Hz-20 kHz the fluctuations in each type of channel showed flat (frequency independent) spectral densities which ranged from 1.1 to 2.4 times the value expected from shot noise. Larger values were obtained at 200 mV membrane potential than at 100 mV, and with 200 mM CsCl than with 1 M CsCl as the bath solution. A likely explanation for the excess noise would be the existence of brief interruptions in the channel current lasting less than 3 microseconds.

Electric Conductivity↗
PubMed1986

Temperature dependence of length of elastin and its polypentapeptide.

Comparison of the temperature dependence of elastomer length of the cross-linked protein, elastin, and of gamma-irradiation cross-linked poly(VPGVG), the polypentapeptide of elastin, with that of latex rubber demonstrate markedly dissimilar behaviors between a classical rubber and the protein and polypeptide elastomers. In the absence of a load latex rubber expands with increasing temperature as is known for classical rubbers comprised of a network of random chains whereas the protein and polypeptide elastomers markedly decrease in length. When under load with a constant applied force, as a classical rubber, latex linearly decreases length with increasing temperature whereas the decrease in length is very non-linear with temperature increase for the protein and polypeptide elastomers. The protein and polypeptide elastomers examined here do not exhibit the characteristic and fundamental temperature dependence of length considered typical of networks of random chains. Accordingly the more complex and even inverse behavior of elastin and the polypentapeptide of elastin in the absence of load require consideration of structural perspectives different from those of a random chain network with negligible interchain interactions.

Amino Acid Sequence↗
PubMed1986

Synthesis, characterization, and black lipid membrane studies of [7-L-alanine] gramicidin A.

With a view to study the relevance of side-chain orientation in the transport of cations through a gramicidin transmembrane channel and to identify an analogue with favorable characteristics, [L-Ala7] gramicidin A was synthesized, purified, verified, and characterized by high-performance liquid chromatography, by carbon-13 and proton magnetic resonance spectra, and by circular dichroism spectra in methanol. Complete incorporation as the channel state was achieved when packaged in lysolecithin-containing lipid bilayers. The single-channel conductance data in diphytanoyllecithin/n-decane membranes are presented along with those of synthetic gramicidin A (GA). [L-Ala7] GA exhibits the highest most probable single-channel conductance so far reported for an analogue occurring at 28 pS as compared to 21 pS for GA under similar conditions. Also, a dramatic reduction in the dispersity of conducting states is observed with about 76% of the events falling in a narrow 1.75-pS conductance window as compared to about 31% of the events for GA under identical conditions. Thus, with the above characteristics, [L-Ala7]GA appears to be a very good candidate for a thorough study of ionic mechanism. The present results indicate that elements intrinsic to the channel proper are rate-limiting for GA and that there is no interfacial polarization or diffusion-controlled association at 1 M KCl and a 100-mV applied potential.

Chromatography, High Pressure Liquid↗
PubMed1986

In vitro calcification and in vivo biocompatibility of the cross-linked polypentapeptide of elastin.

The in vitro calcifiability and molecular weight dependence of calcification of the polypentapeptide, (L X Val1-L X Pro2-Gly3-L X Val4-Gly5)n, which had been gamma-irradiation cross-linked have been determined when exposed to dialyzates of normal, nonaugmented fetal bovine serum. The material was found to calcify: calcifiability was found to be highly molecular weight dependent and to be most favored when the highest molecular weight polymers (n approximately equal to 240) had been used for cross-linking. The in vivo biocompatibility, biodegradability, and calcifiability of the gamma-irradiation cross-linked polypentapeptide were examined in rabbits in both soft and hard tissue sites. The material was found to be biocompatible irrespective of its physical form and to be biodegradable but with n of 200 or less it was not shown to calcify or ossify in the rabbit tibial nonunion model.

Animals↗
PubMed1986

Potassium-39 NMR of K+ interaction with the gramicidin channel and NMR-derived conductance ratios for Na+, K+ and Rb+.

A potassium-39 NMR study of potassium ion interaction with the gramicidin transmembrane channel in phospholipid bilayers at high ion activity is reported which allows determination of a weak binding constant, Kwb approximately equal to 8.3/M, and an off-rate constant for the weak site, kwoff approximately equal to 2.6 X 10(7)/sec. These values are interpreted with the aid of additional NMR data as the binding constant for formation of the doubly occupied channel state and the rate constant for an ion leaving the doubly occupied state. Considering the singly occupied channel state for the potassium ion to be "electrically silent" at 1 molar ion activity, as with the sodium ion, the single-channel conductance for 100 mV and 30 degrees C calculated to be 29 pS, and using the same approximation with previous NMR results on the sodium and rubidium ions, reasonable conductance ratios were calculated. Further experimental estimates of the other three constants with the experimental location of binding sites and Eyring rate theory to introduce voltage dependence allowed a more complete calculation of the two-site channel. The single-channel conductance for potassium ion is calculated to be 24 pS at 1 M activity and 26 pS at 0.6 M activity, which compares for diphytanoyl phosphatidylcholine membranes to an experimental most probable single-channel conductance of 25 pS and a mean channel conductance of 20 pS. The calculated conductance ratios using NMR-derived constants were gamma (K)/gamma (Na) = 2.0 and gamma (Rb)/gamma (Na) = 4.3.(ABSTRACT TRUNCATED AT 250 WORDS)

Electric Conductivity↗
PubMed1986

Polytetrapeptide of elastin. Temperature-correlated elastomeric force and structure development.

High molecular weight polytetrapeptide of elastin, (L.Val1-L.Pro2-Gly3-Gly4)n, was synthesized using activation of the (GGVP) permutation for polymerization. The temperature-dependence of aggregation was characterized as a function of concentration and the circular dichroism spectra were obtained in the 20 degrees to 70 degrees C temperature range. The latter showed an inverse temperature transition centered near 50 degrees C in which polypeptide order increased on raising the temperature. A concentration of 0.6 g of polytetrapeptide in 1 g of water was gamma irradiation cross-linked (20 Mrad) to form an elastomeric matrix. A study of the temperature-dependence of elastomeric force demonstrated a transition toward increased force on raising the temperature with a midpoint of the transition near 50 degrees C. Thus, there is a correlation between increase in intramolecular order and elastomeric force development. These results are compared to previous results on the polypentapeptide of elastin, (VPGVG)n and on an analog, (IPGVG)n, to demonstrate that the temperature of the transition is proportional to the hydrophobicity of the repeating unit. The point is noted that the elastomeric force development correlates better with intramolecular ordering than with intermolecular processes.

Amino Acid Sequence↗
PubMed1985

Infrared spectroscopic studies on gramicidin ion-channels: relation to the mechanisms of anesthesia.

Fourier transform infrared spectroscopic studies are reported on gramicidin ion-channels in phospholipid bilayers and the effects on the spectra of the anesthetics and related compounds (methoxyflurane, halothane, chloroform, carbon tetrachloride, n-pentane and n-decane) have been determined. The addition of anesthetics containing the 'acidic hydrogen' caused unique changes particularly on the amide I bands at 1639 cm-1 and 1670 cm-1. The 1639 cm-1 band became more intense while the intensity near 1670 cm-1 decreased dramatically. These effects were not observed with carbon tetrachloride, n-pentane and n-decane. The 1670 cm-1 band is interpreted as arising from the carbonyls involved in the head-to-head hydrogen-bonded dimerization where the relationship between chains is analogous to that of the antiparallel beta-pleated sheet structure and the anesthetics with 'acidic hydrogens' are considered to disrupt the hydrogen-bonded dimerization by competitive hydrogen bonding to the carbonyls at the head-to-head junction. As the dimer-monomer equilibrium is the 'on-off' mechanism for gramicidin ion-channel conductance, the results are considered in terms of the mechanism of action of anesthetics and are taken to suggest, for certain anesthetics, a hydrogen-bonding role to protein ion-channel components.

Anesthesia↗
PubMed1985

Carbon-13 NMR relaxation studies demonstrate an inverse temperature transition in the elastin polypentapeptide.

Carbon-13 NMR longitudinal relaxation time and line-width studies are reported on the coacervate concentration (about 60% water by weight) of singly carbonyl carbon enriched polypentapeptides of elastin: specifically, (L-Val1-L-[1-13C]Pro2-Gly3-L-Val4-Gly5)n and (L-Val1-L-Pro2-Gly3-L-Val4-[1-13C]Gly5)n. On raising the temperature from 10 to 25 degrees C and from 40 to 70 degrees C, carbonyl mobility increases, but over the temperature interval from 25 to 40 degrees C, the mobility decreases. The results characterize an inverse temperature transition in the most fundamental sense of temperature being a measure of molecular motion. This transition in the state of the polypentapeptide indicates an increase in order of polypeptide on raising the temperature from 25 degrees C to physiological temperature. This fundamental NMR characterization corresponds with the results of numerous other physical methods, e.g., circular dichroism, dielectric relaxation, and electron microscopy, that correspondingly indicate an increase in order of the polypentapeptide both intramolecularly and intermolecularly for the same temperature increase from 25 to 40 degrees C. Significantly with respect to elastomeric function, thermoelasticity studies on gamma-irradiation cross-linked polypentapeptide coacervate show a dramatic increase in elastomeric force over the same interval that is here characterized by NMR as an inverse temperature transition. The temperature dependence of mobility above 40 degrees C indicates an activation energy of the order of 1.2 kcal/mol, which is the magnitude of barrier expected for elasticity.

Amino Acid Sequence↗
PubMed1985

Polypentapeptide of elastin: temperature dependence of ellipticity and correlation with elastomeric force.

Circular dichroism (CD) is used to follow the conformational changes that attend temperature dependent aggregation leading to the viscoelastic (coacervate) state of the polypentapeptide of elastin in water. Two concentrations are used, 2.3 mg/ml and 0.023 mg/ml. The former results in aggregates of a size that exhibit much particulate distortion of the CD spectra whereas the latter results in spectra that are relatively free of distortions. Given the CD spectra of the temperature dependent aggregation of the lower concentration, it is possible to show that the same conformational change is occurring at high concentration. The structure of the polypentapeptide is one of limited order below 20 degrees C which undergoes an inverse temperature transition to a conformation characterized by a regularly recurring beta-turn at 40 degrees C. The temperature profile for the conformational change is compared to the temperature dependence of elastomeric force of gamma-irradiation cross-linked polypentapeptide coacervate. The curves virtually superimpose. When there is little order, there is little elastomeric force and elastomeric force develops to a near maximal value as the repeating Type II beta-turn conformation develops. Not only is the elastomeric state non-random, the more nearly random state has very little elasticity. These results are the inverse of expectations based on the classical theory of rubber elasticity.

Amino Acid Sequence↗