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D W Urry

Publications and source records attributed to D W Urry.

At least 91 records · Page 5Linked to original sources
PubMed1985

Temperature dependence of dielectric relaxations in alpha-elastin coacervate: evidence for a peptide librational mode.

The dielectric permittivity of alpha-elastin coacervate is reported over the frequency range of 1 MHz to 1000 MHz and the temperature dependence from 6.8 degrees C to 70 degrees C is also reported. A temperature-dependent simple Debye-type relaxation is observed with a correlation time of 8 nsec (40 degrees C) which is similar to that of the polypentapeptide of elastin (i.e. 7 nsec at 40 degrees C) where the band has been assigned to a peptide librational mode. By analogy this allows for the first assignment of a peptide librational mode in a naturally occurring polypeptide or protein. The strong spectrally localized band indicates a regularity of structure. The low temperature dependence of the correlation time, giving a 1.7 kcal/mole enthalpy of activation, is consistent with torsional motions associated with a peptide librational mode.

Elastin↗
PubMed1985

Cross-linked polypentapeptide of elastin as a calcifiable matrix: molecular weight dependence.

The polypentapeptide, (L X Val1-L X Pro2-Gly3-L X Val4-Gly5)n, when cross-linked by gamma-irradiation was shown to calcify when exposed to dialysates of calcium and phosphate augmented fetal bovine sera and the molecular weight dependence of this calcification is investigated. Five molecular weight fractions, labeled I to V in order of increasing polymer size from under 12,000 dalton (I), that is, n less than 30, to over 100,000 daltons (V), that is, n greater than 240, were gamma-irradiation cross-linked at 10-12 MRAD to form matrices I-V. Calcium-45 was used to follow the time course and relative amount of calcium uptake from the sera. Scanning electron microscopy and electron probe microanalysis were used to characterize the extent of matrix calcification. All matrices took up calcium-45 from the sera; however, only matrices formed from polypentapeptide with n greater than 100 calcified, that is, matrices III, IV, and V. Matrix V with n greater than 240 calcified massively and in a manner comparable to chemically cross-linked polypentapeptide with n approximately 40 using nonaugmented sera. Presumably, gamma-irradiation results in chain breakage. The gamma-irradiation cross-linked matrices with values of n ranging from under 30 to greater than 240 establish the molecular weight dependence of matrix calcification.

Animals↗
PubMed1985

Secondary structure of the immunoglobulin J chain.

J chain is a 137-residue polypeptide that is covalently linked to polymeric immunoglobulins and participates in their synthesis and transport to external secretions. To clarify these roles, the secondary structure of J chain was characterized by computer-assisted analyses of human and mouse sequences and by circular dichroism measurements of the isolated J chain. The secondary-structure profiles obtained were very similar to those of superoxide dismutase or immunoglobulin light chain variable domains, suggesting that the J chain folds into an eight-stranded antiparallel beta-barrel and should contain approximately 37% beta-sheet conformation, with the rest of the structure existing as reverse turns (random coil). The circular dichroism measurements indicated that the conformation of denatured, S-carboxymethylated or S-sulfonated J chain consists of 75% random coil and 25% beta-structure. Upon reformation of disulfide bonds the percentage of beta-structure in the air-oxidized J chain increased to 34%, a value that is in good agreement with the secondary-structure analysis. Two alternative models of J-chain structure, a two-domain model [Cann, G., Zaritsky, A. & Koshland, M.E. (1982) Proc. Natl. Acad. Sci. USA 79, 6656-6660] and a single-domain antiparallel beta-sheet bilayer model (proposed in this paper), are compared.

Animals↗
PubMed1985

Utilization of 1-hydroxybenzotriazole in mixed anhydride coupling reactions.

The coupling of Boc-Val-OH to either H-Pro-OBzl or H-Pro-Gly-Val-Gly-OBzl by the mixed anhydride method leads to the formation of a urethane by-product in yields of 40-60%. This side reaction can be suppressed by the addition of HOBt to the reaction mixture before the amino component is added. This results in a substantially increased yield of the desired peptide.

Anhydrides↗
PubMed1984

Polypentapeptide of elastin: temperature dependence correlation of elastomeric force and dielectric permittivity.

The polypentapeptide of elastin, (L X Val1-L X Pro2-Gly3-L X Val4-Gly5)n, when gamma-irradiation cross-linked in the coacervate state, is shown by means of thermoelasticity data to be a relatively simple system on which to study polypeptide elasticity. Strikingly, the temperature dependence of the elastomeric force exhibited by cross-linked polypentapeptide coacervate is shown to be proportional to the temperature dependence of the dielectric permittivity of the polypentapeptide coacervate over the critical temperature range of 25 degrees C to 55 degrees C where the force increases five fold. This demonstrates that the mobility of dipolar elements are in large part responsible for the elastomeric force and that dielectric relaxation studies contain the potential for identifying the nature of the dynamic elements responsible for bioelasticity.

Chemical Phenomena↗
PubMed1984

Shortened analog of the gramicidin A channel argues for the doubly occupied channel as the dominant conducting state.

A shortened analog of the gramicidin A transmembrane channel has been synthesized and its transport characterized in planar lipid bilayer membranes. General considerations of a shorter diffusional length and a shorter distance over which the voltage drop occurs (i.e., an increased electric field) would contribute to an increase in single-channel conductance. The finding of a decreased single-channel conductance supports the perspective that the dominant conducting state is the doubly occupied channel wherein distance-dependent repulsion due to the first ion in the channel impedes entry of the second ion in the shorter channel.

Amino Acid Sequence↗
PubMed1984

Dispersity of des-L X Val7-D X Val8-Gramicidin A single channel conductances argues for different side chain orientations as basis.

Planar bilayer studies are reported on the channel activity of des-L X Val7-D X Val8-Gramicidin A. This analog is designed to provide more long-lived side chain distributions involving the Trp residues than occur with Gramicidin A. The carbonyls of these residues coordinate the permeant cation and the energetics of the coordination, which is proposed to depend on side chain orientation, determines the free energies of the rate limiting entrance-exit barriers and the binding sites. The finding of an increased dispersity of single channel conductance for the analog supports the perspective that dispersity derives from different side chain distributions on the same backbone conformation. Channel mechanism is not understood until dispersity is explained.

Electric Conductivity↗
PubMed1984

Temperature dependence of single channel currents and the peptide libration mechanism for ion transport through the gramicidin A transmembrane channel.

A study of the temperature dependence of gramicidin A conductance of K+ in diphytanoyllecithin/n-decane membranes shows the plot of In (single channel conductance) as a function of reciprocal temperature to be nonlinear for the most probable set of conductance states. These results are considered in terms of a series of barriers, of the dynamics of channel conformation, vis-a-vis the peptide libration mechanism, and of the effect of lipid viscosity on side chain motions again as affecting the energetics of peptide libration.

Gramicidin↗
PubMed1984

The source of the dispersity of gramicidin A single-channel conductances. The L X Leu5-gramicidin A analog.

The L X Leu5-gramicidin A analog has been designed, synthesized, and verified for the purpose of testing the perspective that different side-chain distributions are responsible for the dispersity of single-channel conductances. The structural analysis shows that the L . Leu5 analog would limit the possible number of side-chain distributions and that the dispersity of channel conductances would decrease. The finding is the expected decrease in less probable conductance states and the associated increase in the probability of the most probable conductance state.

Electric Conductivity↗
PubMed1984

Val-Gly-Val-Ala-Pro-Gly, a repeating peptide in elastin, is chemotactic for fibroblasts and monocytes.

Recent studies have demonstrated that tropoelastin and elastin-derived peptides are chemotactic for fibroblasts and monocytes. To identify the chemotactic sites on elastin, we examined the chemotactic activity of Val-Gly-Val-Ala-Pro-Gly (VGVAPG), a repeating peptide in tropoelastin. We observed that VGVAPG was chemotactic for fibroblasts and monocytes, with optimal activity at approximately 10(-8) M, and that the chemotactic activity of VGVAPG was substantial (half or greater) relative to the maximum responses to other chemotactic factors such as platelet-derived growth factor for fibroblasts and formyl-methionyl-leucyl-phenylalanine for monocytes. The possibility that at least part of the chemotactic activity in tropoelastin and elastin peptides is contained in VGVAPG sequences was supported by the following: (a) polyclonal antibody to bovine elastin selectively blocked the fibroblast and monocyte chemotactic activity of both elastin-derived peptides and VGVAPG; (b) monocyte chemotaxis to VGVAPG was selectively blocked by preexposing the cells to elastin peptides; and (c) undifferentiated (nonelastin producing) bovine ligament fibroblasts, capable of chemotaxis to platelet-derived growth factor, did not show chemotactic responsiveness to either VGVAPG or elastin peptides until after matrix-induced differentiation and the onset of elastin synthesis. These studies suggest that small synthetic peptides may be able to reproduce the chemotactic activity associated with elastin-derived peptides and tropoelastin.

Animals↗
PubMed1984

D X Ala3 analog of elastin polypentapeptide. An elastomer with an increased young's modulus.

The polypentapeptide , H(L X Val1-L X Pro2-D X Ala3-L X Val4- Gly5 )n Val-OMe which is the D X Ala3 analog of the elastomeric polypentapeptide (PPP) of elastin, (L X Val1-L X Pro2-Gly3-L X Val4- Gly5 )n, has been synthesized. Its conformation is compared to that of the PPP and found to be similar with a somewhat stabilized beta-turn. The D X Ala3 analog coacervates to form a more cohesive viscoelastic material and the coacervate when cross-linked by gamma-irradiation exhibits an approximate doubling of the Young's modulus of elasticity. These results are discussed in connection with other related analogs of the polypentapeptide of elastin, which are non-elastomeric, and found to be consistent with a proposed conformationally based librational entropy mechanism of elasticity.

Elasticity↗
PubMed1983

Infrared spectra of the Gramicidin A transmembrane channel: the single-stranded-beta 6-helix.

IR spectra are reported for preparations of Gramicidin A and malonyl Gramicidin A incorporated as the channel state in phospholipid structures. In this preparation Gramicidin A has already been shown to be unequivocally in the single-stranded beta-helical conformation. The result is an amide I frequency of 1633 +/- 1 cm-1. This demonstrates that the single-stranded beta-helix has an amide I frequency that has previously been considered to be diagnostic of antiparallel double-stranded beta-helix and of beta-sheet structures.

Gramicidin↗
PubMed1983

Supramolecular organization of lysophosphatidylcholine-packaged Gramicidin A.

Heat derived gramicidin A'/L-alpha-lysophosphatidylcholine complexes were separated on a sucrose gradient to form two fractions: Fraction A which had an approximately constant Gramicidin A' to phospholipid ratio of 8 to 10 lipid molecules per Gramicidin A' molecule and Fraction B which had a larger but variable ratio. Fluorescence and circular dichroism studies confirmed Fraction A to be a lipid-incorporated channel state. Electron microscopic studies, using uranyl acetate negative staining, showed fraction A to be a membranous state with the formation of bilayer vesicles, that is, the interaction of peptide and phospholipid micelles causes the lipid to reorganize into a bilayer structure. Freeze-fracture replicas of the channel incorporated state demonstrated the presence of a supramolecular organization of particles exhibiting a tendency to form rows with a 50-60 A periodicity along the row and with 70-80 A distance between rows. An idealized working model for the incorporated state is presented.

Biological Transport↗
PubMed1983

Gramicidin A induces lysolecithin to form bilayers.

Heat-induced association of Gramicidin A with lysolecithin micelles results in the formation of lipid bilayer structures. The capacity of the Gramicidin A peptide to transform the lysolecithin lipid structure from micelle to bilayer is considered in terms of molecular packing mechanisms and relevance to membrane processes in general. The resulting lipid-bilayer-packaged channel system has particular usefulness in characterizing channel structure and mechanism.

Chemical Phenomena↗
PubMed1983

D-Ala5 analog of the elastin polypentapeptide. Physical characterization.

The D-Ala5 analog, (L-Val1-L X Pro2-Gly3-L X Val4-D-Ala5) of the polypentapeptide (PPP) of elastin is synthesized and characterized by a series of physical methods. Carbon-13 and proton nuclear magnetic resonance spectroscopies are used to verify purity and, by means of solvent dependence of peptide C-O chemical shift and of temperature dependence of peptide NH chemical shift, to establish by comparison with the PPP of elastin the presence and increased stability of the Type II Pro2-Gly3 beta-turn. The temperature dependence of aggregation in water to form a viscoelastic phase called the coacervate is reported for several concentrations. Comparison of carbon-13 nuclear magnetic resonance spectra obtained under identical conditions for the coacervate states of the PPP of elastin and the D-Ala5 analog shows the effect of replacing the Gly5 residue by a D-Ala5 residue to be one of greatly restricting mobility of the polypeptide chain. Scanning electron micrographs, of the coacervate alone and of the coacervate cross-linked and compounded to a Dacron fabric before and after stress-strain studies, are reported which show the D-Ala5 PPP matrix to rupture during the stresses of drying and of stretching while wet. Thus, the effect of adding a methyl moiety to the Gly5 residue of the PPP of elastin is to decrease markedly the mobility of the polypeptide chain and to destroy elasticity. The results are presented as a test of the proposed librational entropy mechanism of elasticity of the PPP of elastin.

Crystallization↗
PubMed1983

Synthesis and characterization of (1-13C) Phe9 gramicidin A. Effects of side chain variations.

The synthesis of (1-13C)-Phe9-gramicidin (90% enriched) was carried out by the solid phase method. The peptide was removed from the resin by treatment with ethanolamine, deblocked, formylated and purified by preparative t.l.c. to obtain the gramicidin analog in an overall yield of 24%. The peptide was verified and characterized by high pressure liquid chromatography, carbon-13 nuclear magnetic resonance, circular dichroism and single channel currents. Single channel conductances were found to be similar to those of (1-13C)-Phe11-GB but significantly lower than that of gramicidin A. When this gramicidin analog was incubated with phospholipid, the characteristic channel spectrum was not obtained and interaction with sodium ion was not observed. A possible explanation for this behavior is discussed.

Amino Acid Sequence↗
PubMed1983

Use of synthetic gramicidins in the determination of channel structure and mechanism.

The syntheses of (1-13C) Trp9 gramicidin A (GA), (1-13C) Trp11 GA, (1-13C) Trp13 GA, (1-13C) Trp15 GA, and D . Leu2 GA are verified by means of high performance liquid chromatography, carbon-13 nuclear magnetic resonance, circular dichroism and characterization of transport properties. The use of these and other synthetic gramicidins is discussed in terms of determining ion binding sites within the channel, helix sense of the channel, the basis of monovalent vs divalent cation selectivity, and means of modulating channel conductance.

Gramicidin↗