Ca²⁺ binding cyclic octapeptides having an alternating sar and a hydrophobic amino acid in the sequence

Abstract

Cyclic octapeptides having alternating Sar and hydrophobic amino acid sequences, such as cyclo[Lys(Z)-Sar-Leu-Sar-Leu-Sar-Leu-Sar] (C8KL), cyclo[Glu(OMe)-Sar-Lys(Z)-Sar-Leu-Sar-Leu-Sar] (C8KE, and cyclo[Lys(Suc)-Sar-Leu-Sar-Leu-Sar-Leu-Sar] [C8K(Suc)L, Suc represents succinic acid], were synthesized. These cyclic octapeptides formed a complex selectively with Ca2+. Upon complexation, trans peptide bonds of Sar residues were isomerized to cis peptide bonds. C8KL and C8KE showed very similar characteristics of Ca2+ binding, extraction of Ca2+ from an aqueous solution to a chloroform solution, and Ca2+ transport through a liquid chloroform membrane. C8KL transported Ca2+ across the lipid bilayer membrane above the phase-transition temperature, while C8KE and C8K(Suc)L did not. Therefore, the transport of Ca2+ through the lipid bilayer membrane is very sensitive to the hydrophobicity of the carrier molecule.

Modulation of phospholipase A2 activity by the tumour promoters phorbol esters and teleocidin

“…Preparation of DPPC vesicles encapsulating Quin 2 DPPC vesicles encapsulating Quin 2 were prepared as described previously (Kimura et al, 1989). DPPC was dispersed in Hepes, pH 7.4, containing 0.1 M-NaCl and 20 mM-Quin 2, sonicated and centrifuged at 100000g.…”

Translocation of Ca2+ across lipid bilayer membrane due to defects induced by teleocidin

“…Thin lipid film formed on the wall of a round-bottomed flask was dispersed in buffer (10 mM Hepes, 0.1 M NaC1, pH 7.4) containing Quin 2 (20 raM), and was sonicated above the phasetransition temperature of the membrane and centrifuged at 100 000 g. Free Quin 2 was removed by gel chromatography on a Sephadex G-75 column (1 x 25 cm) to obtain Quin 2-encapsulated DPPC vesicles (Quin 2 vesides) [7]. Quin 2 vesicles were incubated in the medium containing metal ion, and the change of fluorescence intensity caused by the additives was measured on a Hitachi MPF-4 spectrophotometer (Japan).…”