Cation-binding properties of ionophorous cyclic octapeptide in acetonitrile solution.

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概要

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• Complex formation of synthetic cyclic octapeptide, cyclo[Gly–L-Lys(Z)–Sar–L-Pro]<SUB>2</SUB>, with alkali and alkaline earth metal ion was investigated by CD and NMR spectroscopy. Titration curves obtained from CD data revealed three kinds of CGLSP2(P)/cation(C) complexes. P<SUB>2</SUB>C ("peptide sandwich"), PC ("1:1"), and PC<SUB>2</SUB> ("cation sandwich") complexes occurred in the complexation between CGLSP2 and Ba<SUP>2+</SUP>. In the presence of Li<SUP>+</SUP>, Mg<SUP>2+</SUP>, or Ca<SUP>2+</SUP>, the existence of PC and PC<SUB>2</SUB> was assumed. K<SUP>+</SUP> and Na<SUP>+</SUP> form only a PC species with CGLSP2. By analyzing the titration curves, 1 :1 complex-formation constants (<I>K</I><SUB>1</SUB>) were evaluated. The <I>K</I><SUB>1</SUB> values decrease in the order Ba<SUP>2+</SUP>>Ca<SUP>2+</SUP>>Mg<SUP>2+</SUP>>Li<SUP>+</SUP>>>Na<SUP>+</SUP>, K<SUP>+</SUP>. <SUP>1</SUP>H- and <SUP>13</SUP>C-NMR data showed that CGLSP2 in acetonitrile exists in at least five different conformational states in a free state. A predominant conformer had a C<SUB>2</SUB>-symmetric structure containing two cis Lys–Sar peptide bonds. After the addition of equimolar amounts of Ba(ClO<SUB>4</SUB>)<SUB>2</SUB>, these conformations converged into a single C<SUB>2</SUB>-symmetric one with all-trans peptide bonds. This corresponds to a PC species. On further addition of the salt, CGLSP2 changed the conformation into an asymmetric structure with one cis Lys–Sar peptide bond. This corresponds to a PC<SUB>2</SUB> species.

• 公益社団法人 日本化学会の論文

著者

• TSUDA Keishiro

  Research Institute for Polymers and Textiles

• TANAKA Yoshio

  Research and Development Center, Shinryo Corporation

• Shimizu Toshimi

  Research Institute for Polymers and Textiles

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