title: Influence of helix formation on cis/trans isomerism of Xaa-Pro bonds flanking the helical segment.
abstract: The trifluoroethanol (TFE)-induced formation of alpha-helical structures in the peptide hormone calcitonin (salmon) was studied using limited proteolysis combined with capillary zone electrophoresis. A low TFE content in TFE/buffer mixtures was insufficient to introduce secondary structure, but two Lys-Leu bonds were found to have become inaccessible to proteolysis with clostripain. The influence of increasing helical degree of the Thr6-Lys18 (or Thr6-Tyr22 in the trans conformation) segment on the cis/trans isomerization of the adjacent Tyr22-Pro23 peptide bond was examined by means of isomer specific proteolysis. Results indicate that the helix dipole does not influence the cis/trans equilibrium distribution of the flanking Tyr22-Pro23 bond but considerably increases its isomerization rate Ko-->t.
authors.affiliation: Max-Planck-Gesellschaft, Arbeitsgruppe, Enzymologie der Peptidbindung, Halle/Saale, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Meyer
authors.forename: M
authors.initials: M
authors.lastname: Drewello
authors.forename: G
authors.initials: G
authors.lastname: Fischer
mesh_terms: D000595:Amino Acid Sequence; D002116:Calcitonin / Q000737:chemistry*; D002942:Circular Dichroism; D006868:Hydrolysis; D007536:Isomerism; D007700:Kinetics; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary
chemical_list: C028815:salmon calcitonin; D002116:Calcitonin