A 25-mer cationic peptide pleurocidin, isolated from the winter¯ounder, has broad antibacterial activity. To clarify the structure±activity relationship, its properties and biological activity were examined. CD measurements showed that pleurocidin took an a-helical structure in the presence of DOPC/DOPG (3 : 1, anionic) vesicles. Very weak hemolytic activity of pleurocidin was observed and its antibacterial activity was moderate. Tryptophan¯uorescence shift measurements showed that pleurocidin interacted weakly with a neutral phospholipid, but strongly with an acidic phospholipid. The peptide exhibited weak dye-leakage activity for DOPC (neutral) vesicles and moderate activity for acidic vesicles. From experiments on dye-leakage activity and membrane translocation of the peptide, it seemed likely that pleurocidin, like magainin 2, forms pores in the lipid membrane. A study of amino acid substitution in pleurocidin revealed that a-helicity, rather than hydrophobicity, affects the properties and activity of the peptide. Abbreviations: CD, circular dichroism; DNS-PE, N-dansyl-DL-3-phosphatidylethanolamine; DOPC, dioleoyl-DL-3-phosphatidylcholine; DOPG, dioleoyl-DL-3-phosphatidylglycerol; FITC,¯uorescein isothiocyanate; MALDI-TOF-MS, matrix-assisted laser desorption/ionization time of¯ight mass spectrometry; MIC, minimum inhibitory concentration; MLV, multilamellar vesicle; M2, magainin 2; NBD-PE, N-(7-nitro-benz-2-oxa-1,3-diazole-4-yl)dipalmitoyl-3-phosphatidylethanolamine; Ple, pleurocidin; RP-HPLC, reversed phase high-performance liquid chromatography; SUV, small unilamellar vesicle; TFE, 2,2,2-tri¯uoroethanol; TSB, tryptic soy broth.
Magainin 2 (M2) forms pores by associating with several other M2 molecules in lipid membranes and shows antibacterial activity. To examine the effect of M2 dimerization on biological activity and membrane interaction, parallel and antiparallel M2 dimers were prepared from two monomeric precursors. Antibacterial and haemolytic activities were enhanced by dimerization. CD measurements showed that both dimers and monomers have an alpha-helical structure in the presence of lipid vesicles. Tryptophan fluorescence shift and KI quenching studies showed that all the peptides were more deeply embedded in acidic liposomes than in neutral liposomes. Experiments on dye-leakage activity and membrane translocation of peptides suggest that dimers and monomers form pores through lipid membranes, although the pore formation may be accompanied by membrane disturbance. Although dimerization of M2 increased the interaction activity with lipid membranes, no appreciable difference between the activities of parallel and antiparallel M2 dimers was observed.
Potential scattering of slow electrons in a weak external electromagnetic field is examined. An expression for the relation between the amplitudes of the n-photon laserinduced free-free transition ( FFT) and electron elastic scattering has been obtained. The many-photon FFT has been numerically calculated in the case of electron scattering by model potentials. The results of calculating the one-photon FFT cross sections are compared with the results of calculations using well known formulae.
Hydrogen in Metals J Pd -Cu Binary and Pd -Cu-Au Ternary Solid Solution Alloys p-c Isotherms J ThermodynamicsThermodynamic quantities for absorption of hydrogen by Pd-Cu alloys with up to atom fraction of Xc, = 0.2, and by Pd -Cu-Au ternary alloys with up to (Xc, + XAu) = 0.2, where X,, = XAu, have been determined at temperatures between 273 K and 423 K and hydrogen pressures up to 1000 Torr by measurements of the pressure-composition isotherms. The hydrogen absorption characteristics of these alloys have been compared with that of the previously reported Pd -Au binary alloys. The room temperature lattice parameters of hydrogen-free Pd -Cu -Au alloys increases with the solute content, albeit by a small amount. The relative partial molar enthalpy, AH!, at infinite dilution in Pd-Cu-Au alloys increases in exothermicity with increasing (Cu + Au) content, and the alloy composition dependence of the AH! value falls near the mid-points between those of each Pd-Cu and Pd-Au binary alloy. The relative partial molar entropy, Ash, at infinite dilution in Pd -Cu -Au alloys decreases with the solute content, and the AS! values at the same alloying content are larger than that of Pd-Au alloys, but are smaller than that of Pd -Cu alloys. The [H -Cu + H -Au] pair interaction energies between the dissolved hydrogen and the substitutional solute atoms in the ternary alloys have been evaluated according to a quasi-chemical model with zeroth order approximation by taking into account the "constant pressure" to "constant volume" correction. The hydrogen solubility behaviour at low hydrogen concentration in Pd-Cu-Au ternary alloys can be described as due to the counteraction of the repulsive H-Cu pair interaction and the attractive H -Au pair one in the Pd host lattice. The stability of the P-phase hydride at a given temperature in Pd-Cu-Au alloys decreases with the solute content, and the alloy composition dependence of the stability is also placed near the mid-points between those for each Pd-Cu and Pd-Au binary alloy.
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