Anion Transport in Liposomes Responds to Variations in the Anchor Chains and the Fourth Amino Acid of Heptapeptide Ion Channels.

Seven heptapeptide derivatives have been prepared. The peptide structure is (Gly)(3)Xxx(Gly)(3) in which Xxx stands for a variable amino acid. The amino acid variations include azetidine carboxylic acid, pipecolic acid, meta-aminobenzoic acid, proline, and leucine. All seven compounds have a C-terminal benzyl group. In all cases, the heptapeptide's N-terminus was linked to diglycolic acid and a dialkylamine. In five cases, the N-terminal group was didecylamine and in two cases, N-ethyl-N-decyl. Chloride and carboxyfluorescein release from phospholipid vesicles was studied with the result that C(10)H(21)N(C(2)H(5)) COCH(2)OCH(2)CO-NH-(Gly)(3)Leu(Gly)(3)-OCH(2)Ph was the most active. Hill analysis showed that this compound involves pore formation by four monomer units rather than two, as previously found for other members of this family.