Collect. Czech. Chem. Commun. 1982, 47, 3437-3446

Conformation of branched polypeptides based on poly(L-lysine). Effect of the ionic strength and of the presence of alcohols

Hana Votavováa, Ferenc Hudeczb, Jaroslav Šponara, Karel Bláhaa and Mária Szekerkeb

a Institute of Organic Chemistry and Biochemistry, Czechoslovak Academy of Sciences, 166 10 Prague 6, Czechoslovakia
b Research Group for Peptide Chemistry, Hungarian Academy of Sciences, Budapest, Hungary


CD spectra of branched polypeptides based on poly(L-lysine) containing in the side chains approximately, 3, 5 and 8.5 DL-alanine residues or 3 DL-alanine residues and another terminal L-amino acid were measured at pH 7.4, and in the uncharged state in various ionic strengths, and also in water-methanol and water-trifluoroethanol mixtures. At pH 7.4 and in low ionic strength (0.02M and 0.2M-NaCl) the polypeptides assume an unordered conformation, except for the L-leucine containing polypeptide, which is helical to a considerable extent. Increase of the ionic strength to 2.0M-NaCl leads to the formation of the α-helical structure. In the uncharged state all polypeptides are at least partly helical. The content of the α-helix increases with increasing ionic strength and depends also on the nature of the side chain. Formation of the α-helix is supported by the presence of L-leucine and L-proline, some limitation of the α-helix formation by histidine is manifested mainly in low ionic strength. The presence of methanol and trifluoroethanol has an effect similar to the increase of ionic strength, i.e. increases the α-helix content.