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Biomedical subjects

D W Urry

Publications and source records attributed to D W Urry.

At least 145 records · Page 8Linked to original sources
PubMed1978

Hydrogen-deuterium substitution and solvent effects on the nitrogen-15 nuclear magnetic resonance of gramicidin S: evaluation of secondary structure.

Complete assignments of nitrogen-15 resonances of gramicidin S have been made in dimethyl sulfoxide, trifluoroethanol, and in a solvent mixture of dimethyl sulfoxide (50%) and methanol (50%). The assignments are achieved by utilizing the secondary structure of gramicidin S, by comparing the nitrogen-15 spectrum of gramicidin S with that of di-N-methylphenylalanine-gramicidin S and by taking into account the distinguishable value of nitrogen-15 chemical shift for valine in model compounds. Deuterium substitution for labile peptide protons was performed to delineate solvent shielded and deshielded peptide nitrogens and to substantiate further the signal assignments. The solvent titration on going from dimethyl sulfoxide to trifluoroethanol was also performed and shown to have a large deshielding effect on the peptide nitrogen whose corresponding peptide carbonyl, within the peptide moiety, was accessible to the trifluroethanol solvent.

Deuterium↗
PubMed1978

Basic aspects of calcium chemistry and membrane interaction: on the messenger role of calcium.

To summarize the perspective developed in this lecture we begin by considering it as axiomatic: (1) that aqueous domains delimited by lipid membranes typify cellular structure; (2) that different compositions of extracellular and intracellular aqueous domains and differences among intracellular aqueous domains require selective permeation of lipid membranes; and (3) that inorganic ion movements across lipid membranes are a common denominator in permeation. This set of axioms lead to the following set of postulates: (1) Evolutionary solutions to the problematic apposition of ions and lipid barriers are fundamental aspects of cell function. (2) An effective messenger role for communication between aqueous domains requires (a) meticulous modulation of movement across lipid membranes and (b) selective interactions within aqueous domains. (3) An ion would be an effective messenger. In a search for an appropriate ionic messenger it is noted that inorganic cations have a wider range of interactions with biomolecules than anions, that the prevalent monovalent cations have too high a flux across lipid membranes and too weak an interaction with molecules in aqueous domains, that trivalent cations cannot as effectively be transported across lipid membranes, that divalent cation movement across lipid membranes can be well modulated and their divalent charge allows for a wide range of binding constants with biological molecules, and that for reasons of radius-compatibility with polypeptide chelation and due to the lack of stringent crystal field requirements, Ca2+ is a most suitable divalent cation for a messenger role.

Anti-Bacterial Agents↗
PubMed1978

Channel structures of gramicidin: characterization of succinyl derivatives.

Succinyl derivatives of gramicidin were tested for their ability to form channels in planar artificial lipid bilayers. Both N-succinyldeformylgramicidin methyl ester and charged O-succinylgramicidin formed channels, but the channels had markedly different sizes and lifetimes. This implies that gramicidin forms channels by end-to-end association. However, the doubly charged N,O-bissuccinyldeformylgramicidin was inactive, which suggests that only end-to-end association of gramicidin may result in channel formation.

Electric Conductivity↗
PubMed1978

A theoretical study of Na+ and Mg+2 binding to the carbonyl oxygen of N-methyl acetamide.

Molecular orbital calculations (CNDO/2) are reported for the interaction of Na+ and Mg+2 with the carbonyl of a model peptide moiety (N-methyl acetamide) as a function of the C--O ... Me distance and angle and with variation in the number of ligands for the purpose of determining the steepness of the distance dependence of the binding energy and for the purpose of determining the reduction of charge on the ion with increasing numbers of ligands. The greater energy derived on divalent ion binding and the steeper distance dependence indicate that selective, divalent over monovalent, ion binding will occur whenever the liganding system can provide a coordination shell of appropriate dimension. The calculations indicate that the preferred C--O ... Me angle is not 180 degrees. Of particular note is the decrease of charge on the cation on binding to N-methyl acetamide. One ligand bound to Na+ reduces the charge from 1.0 to 0.7 electron units and four ligands bound to Mg+2 reduces the charge from 2.0 to 0.7 electron units. This is of primary significance in carrier and channel mechanisms for cation permeation of lipid membranes; and although the numerical values are qualitative, the implication is for allowance of multiple occupancy of channels by monovalent cations.

Acetamides↗
PubMed1978

Coacervation properties in sequential polypeptide models of elastin. Synthesis of H-(Ala-Pro-Gly-Gly)n-Val-OMe and H-(Ala-Pro-Gly-Val-Gly)n-Val-OMe.

Syntheses of two sequential polypeptides H-(Ala-Pro-Gly-Gly)n-Val-OMe and H-(Ala-Pro-Gly-Val-Gly)n-Val-OMe via the p-nitrophenyl active ester procedure are reported. The two polymers were obtained in good yields and the polymers were shown to be of large molecular weights, n greater than 40. These two polypeptides were synthesized as analogs of the two coacervating sequential polypeptides H-(Val-Pro-Gly-Gly)n-Val-OMe, and H-(Val-Pro-Gly-Val-Gly)n-Val-OMe, in which the Val-l residue is replaced by an Ala-l residue. H-(Ala-Pro-Gly-Gly)n-Val-OMe did not coacervate even at as high a temperature as 100 degrees, and H-(Ala-Pro-Gly-Val-Gly)n-Val-OMe did not coacervate; however, it precipitated irreversibly around 65--70 degrees C. This suggests the critical role of the Val-Pro hydrophobic side chain interaction in coacervation.

Amino Acid Sequence↗
PubMed1978

Coacervation of sequential polypeptide models of tropoelastin. Synthesis of H-(Val-Ala-Pro-Gly)n-Val-OMe and H-(Val-Pro-Gly-Gly)n-Val-OMe.

Syntheses of two sequential polytetrapeptide models, H-(Val-Ala-Pro-Gly)n-Val-OMe and H-(Val-Pro-Gly-Gly)n-Val-OMe via the p-nitrophenyl ester method are described. The p-nitrophenyl ester method gave high yields (85%--100%) of large molecular weight polymers. H-(Val-Pro-Gly-Gly)n-Val-OMe exhibited the interesting property of coacervation on raising the temperature of aqueous solutions while H-(Val-Ala-Pro-Gly)n-Val-OMe precipitates irreversibly under similar conditions. Whereas non-dialyzed lower molecular weight polymers of H-(Val-Pro-Gly-Gly)n-Val-OMe with n = 8 to 40 did not coacervate, but did show a transition to increased intramolecular order on raising the temperature of aqueous solutions above 50 degrees C, the dialyzed higher molecular weight polymer, n greater than 40, does coacervate beginning at about 50 degrees C. This demonstrates the molecular weight dependence of coacervation and also suggests the importance to coacervation of side chain interactions in the Val-Pro sequence. The increase in intramolecular order, seen as the formation of a 14-atom hydrogen-bonded ring, occurs simultaneously with the Val-Pro hydrophobic side chain association.

Amino Acid Sequence↗