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A R Atkins

Publications and source records attributed to A R Atkins.

16 recordsLinked to original sources
PubMed1991

Conformation of sarafotoxin-6b in aqueous solution determined by NMR spectroscopy and distance geometry.

The solution structure of sarafotoxin-6b in water has been determined using high-resolution NMR spectroscopy. 127 proton-proton distance measurements and three phi dihedral angle constraints derived from NMR spectra were used to calculate the solution structure using a combination of distance geometry and restrained molecular dynamics. The major structural feature of the resulting family of five structures was a right-handed alpha-helix extending from K9 to Q17. In contrast, the C-terminal region of the peptide appears not to adopt a preferred conformation in aqueous solution. The present structure is compared with those previously determined for endothelin peptides in non-aqueous solvents.

Amino Acid Sequence↗
PubMed1990

Solid-state 13C-NMR studies of the effects of sodium ions on the gramicidin A ion channel.

End-to-end helical dimers of gramicidin A form transmembrane pores in lipid bilayers, through which monovalent ions may pass. The groups within the peptide that interact with these ions have been studied by application of solid-state spectroscopic methods to a series of gramicidin A analogues synthesized with 13C in selected peptide carbonyl groups. The resonances of D-Leu10, D-Leu12 and D-Leu14 analogues were perturbed in the presence of 0.16 M sodium ions, whereas the resonances of the carbonyls of Gly2, Ala3, D-Leu4 and Val7, which are closer to the formylated N-terminal end of the peptide, were unaffected. The observed changes in chemical shift anisotropy are indicative of a change in orientation of the abovementioned leucine carbonyls.

Dimyristoylphosphatidylcholine↗
PubMed1990

Shark myelin basic protein: amino acid sequence, secondary structure, and self-association.

Myelin basic protein (MBP) from the Whaler shark (Carcharhinus obscurus) has been purified from acid extracts of a chloroform/methanol pellet from whole brains. The amino acid sequence of the majority of the protein has been determined and compared with the sequences of other MBPs. The shark protein has only 44% homology with the bovine protein, but, in common with other MBPs, it has basic residues distributed throughout the sequence and no extensive segments that are predicted to have an ordered secondary structure in solution. Shark MBP lacks the triproline sequence previously postulated to form a hairpin bend in the molecule. The region containing the putative consensus sequence for encephalitogenicity in the guinea pig contains several substitutions, thus accounting for the lack of activity of the shark protein. Studies of the secondary structure and self-association have shown that shark MBP possesses solution properties similar to those of the bovine protein, despite the extensive differences in primary structure.

Amino Acid Sequence↗
PubMed1989

Effect of acyl chain length on the structure and motion of gramicidin A in lipid bilayers.

The transmembrane ion transport properties of gramicidin A have previously been shown to dependent on the nature of its lipid environment. Solid-state NMR spectroscopic studies of 13C-labelled analogues of gramicidin in oriented multilayers of phosphatidylcholine have shown that variation of the lipid hydrocarbon chain length has no effect on the structure or orientation of the peptide backbone.

Carbon Isotopes↗
PubMed1989

Determination of the structure of a membrane-incorporated ion channel. Solid-state nuclear magnetic resonance studies of gramicidin A.

Solid-state nuclear magnetic resonance (NMR) measurements on 13C-labeled analogues of the ion channel-forming peptide, gramicidin A, have been used to directly determine the structure of this peptide in lipid membranes. Seven gramicidin analogues, each labeled in a single carbonyl group of gly2, L-ala3, D-leu4, L-val7, D-leu10, D-leu12, or D-leu14 were synthesized by the solid-phase method. These gramicidin analogues were incorporated into aligned multilayers of dimyristoylphosphatidylcholine, or diether lipid bearing 14- or 16-carbon chains, at a 1:15 peptide:lipid mole ratio. Proton-enhanced, 13C, solid-state spectra were obtained at several temperatures and over a range of sample orientations with respect to the spectrometer magnetic field to permit accurate measurement of the chemical shift anisotropies. The observed anisotropies indicate that all of the labeled carbonyl bonds are oriented almost parallel to the molecular long axis and perpendicular to the lipid bilayer plane. These orientations are consistent with gramicidin forming a beta 6.3 single-strand helix that is oriented parallel to the methylene chains of the lipid molecules. Comparison of the linewidths from labeled residues that are in the innermost turn of the helix (gly2, ala3, and D-leu4), in the center of the molecule (val7), and in the turn nearest the lipid bilayer surface (D-leu10, D-leu12, and D-leu14) suggests that although the peptide behaves largely as a rigid barrel, segments of the peptide close to the membrane surface possess greater motional freedom. At temperatures above the gel-to-liquid crystalline transition temperature (Tc) the gramicidin molecules rotate, with a less than millisecond correlation time, about the bilayer normal: several degrees below Tc they become immobile on the NMR timescale, without change in the channel conformation. In the L beta' phase the linewidths of the D-leu10, D-leu'2, and D-leu" resonances become equal to those of the other labeled sites, indicating reduced but equivalent motion for all of the peptide carbonyl groups.

Amino Acid Sequence↗
PubMed1977

A ten-year study of carcinoma of the pancreas.

During the 10 years from 1965 through 1974, 86 patients with adenocarcinoma of the pancreas were diagnosed or referred for treatment at the University of Oregon Health Sciences Center. The average age and survival in these patients is not significantly different from other published series. Only four patients had resectable tumors, and of these two survived over twelve months. Eight other patients also survived over twelve months, and no two of these had the same treatment regimens (although nine of the ten long-term survivors received some form of chemotherapy). Fourteen patients received a combination of chemotherapy and radiation therapy. While their average survival was only two months longer than that of the entire series, three were long-term survivors. Over 75% had significant palliation; this suggests that this treatment should be considered in selected cases.

Adenocarcinoma↗