Influence of helix formation on cis/trans isomerism of Xaa-Pro bonds flanking the helical segment.
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.
Meyer
S
S
Max-Planck-Gesellschaft, Arbeitsgruppe, Enzymologie der Peptidbindung, Halle/Saale, Germany.
Drewello
M
M
Fischer
G
G
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
C028815:salmon calcitonin; D002116:Calcitonin