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2-chloroethanol is used as reference solvents for characterizing

Time:2015/11/25 5:54:16

Infrared spectroscopic study of the secondary structure of melittin in water, 2-chloroethanol, and phospholipid bilayer dispersions

The conformations of melittin, an amphipathic polypeptide consisting of 26 amino acid residues, and its hydrophobic (residues 1--19) and hydrophilic (residues 20--26) fragments were examined in various solvent systems, including H2O, 2H2O, 2-chloroethanol, and 1,2-dimyristoylphosphatidylcholine (DMPC) multilayers, by infrared spectroscopy. Water and 2-chloroethanol were used as reference solvents for characterizing the amide I and II vibrational frequencies of the polypeptide in systems reflecting unordered, beta-structure, or alpha-helical forms. In DMPC bilayer assemblies both melittin and its hydrophobic fragment F1 exhibit alpha-helical conformations. In contrast, infrared spectra for the hydrophilic F2 fragment are suggestive of a beta conformation with perhaps spectral contributions from random-coil configurations. The alpha-helical conformation of intact melittin in DMPC multilayer dispersions remains unchanged as the bilayer passes from the gel to liquid-crystalline state. For melittin-water solutions the infrared spectra monitor changes in population of specific conformations as the temperature is varied. Thus, for melittin concentrations in which tetramers are dominant high temperatures (31 degrees C) favor the alpha-helical form, while low temperatures (8 degrees C) lead to populations of both beta and alpha-helical structures. At lower melittin concentrations for which monomers persist, high temperatures favor an unordered polypeptide form, while low temperatures induce an alpha-helical conformat

involvement of a quinoprotein alcohol-dehydrogenase and an nad-dependent aldehyde dehydrogenase in 2-chloroethanol metabolism in xanthobacter-autotrophicus gj10

ABSTRACT An inducible methanol dehydrogenase showing high activity with 2-chloroethanol was purified from 2-chloroethanol-grown cells of the 1,2-dichloroethane utilizing bacterium Xanthobacter autotrophicus GJ10. The enzyme consisted of a 60 kDa polypeptide that was associated with a 10 kDa polypeptide and contained pyrrolo-quinoline quinone (PQQ) as a prosthetic group. Chloroethanol-grown cells of strain G J 10 also contained an inducible NAD-dependent chloroacetaldehyde dehydrogenase. Its involvement in the metabolism of 2-chloroethanol was inferred from its absence in a 2-chloroethanol non-utilizing mutant. Three different isolates of X. autotrophicus that do not utilize 2-chloroethanol for growth produced chloroethanol dehydrogenase and chloroacetaldehyde dehydrogenase activities at similar levels as strain GJ10. It is concluded that both dehydrogenases are involved in the metabolism of natural compounds and due to their broad substrate specificity fortuitously also play a role in the metabolism of the xenobiotic compounds 1,2-dichloroethane and 2-chloroethanol.