Showing papers by "Thorgeir E. Thorgeirsson published in 1996"

Direct determination of the membrane affinities of individual amino acids.

Abstract: Amino acids have distinct lipid bilayer affinities which influence the insertion and topology of membrane-bound polypeptides and proteins. To measure membrane affinities, 14 uncharged amino acids were introduced individually at a guest site in a 25-residue peptide derived from the membrane-binding presequence of yeast cytochrome c oxidase, and the peptides were labeled with a nitroxide spin-label. The free energies of transfer from phospholipid bilayers to water (delta delta Gbilayer) were determined directly by examination of partitioning into phospholipid bilayers using electron paramagnetic resonance. The delta delta Gbilayer values are in agreement with hydrophobicities assessed from 1-octanol-water partitioning of N-acetyl amino acid amides [Fauchere, J.-L., & Pliska, V. (1983) Eur. J. Med. Chem. 18, 369-375; Eisenberg, D., & McLachlan, A. (1986) Nature 319, 199-203] and quantitatively demonstrate the role of the hydrophobic effect in membrane-protein interactions.

Temperature dependence of polypeptide partitioning between water and phospholipid bilayers.

Abstract: Various thermodynamic forces (eg, the hydrophobic effect, electrostatic interactions, peptide immobilization, peptide conformational changes, “bilayer effects,” and van der Waals dispersion forces) can participate in the transfer of polypeptides from aqueous solution into lipid bilayers To investigate the contributions of these forces to peptide−membrane thermodynamics, we have studied the temperature dependence of the water−bilayer partitioning of 4 polypeptides derived from the first 25 amino acid residues in the presequence of subunit IV of yeast cytochrome c oxidase (Cox IVp) using electron paramagnetic resonance spectroscopy The partitioning of the Cox IVp peptides into phospholipid bilayers increases as the temperature is increased from 3 to 40 °C The contribution of bilayer surface expansion to the temperature-dependent partitioning is estimated to be relatively small and to contribute minimally to the increased bilayer binding of the peptides with increasing temperature Thermodynamic analysi