title: Beta-structures of polypeptides with L-and D-residues. Part I. Synthesis and conformational studies.
abstract: A series of five alternating poly(leucyl-lysyl) samples with varying amounts of L-and D-residues randomly distributed along the chain, but evenly shared out amongst leucyl and lysyl residues were synthesized by condensation of a mixture of the four diastereoisomeric dipeptide p-nitro-phenylesters. Their behavior in aqueous solution at various ionic strengths was studied by infrared spectroscopy which allowed measurement of the total amount of beta-structures, and by circular dichroism which gives the excess of L-residues over D-residues in the same structures. Comparison with the properties of the all L-poly(Lys-Leu-Lys-Leu) shows that incorporation of a few D-residues in a L-chain seems to reduce the width of the beta-sheets obtained in presence of salt. Higher proportions of D-isomers prevent the coil leads to beta transition from occurring when the ionic strength is increased except for segments containing at least 6 to 7 adjacent residues of the same configuration.
mesh_terms: D002942:Circular Dichroism; D007536:Isomerism; D007930:Leucine; D008239:Lysine; D008433:Mathematics; D009842:Oligopeptides; D010455:Peptides / Q000138:chemical synthesis; D011487:Protein Conformation; D013055:Spectrophotometry, Infrared; D013329:Structure-Activity Relationship
chemical_list: D009842:Oligopeptides; D010455:Peptides; D007930:Leucine; D008239:Lysine