Channel‐Forming Activity of 3‐Hydroxybutanoic‐Acid Oligomers in Planar Lipid Bilayers

Monodisperse and polydisperse oligomers and polymers of 3‐hydroxybutanoic acid (3‐HB) containing 8, 16, ca. 28, 32, ca. 60, 64, 96, and ca. 3000 monomer units were incorporated into palmitoyl‐oleoyl‐phosphatidyl choline (POPC) planar bilayers. At concentrations of 0.1–5% of oligo(3‐HB), the resulting phospholipid bilayers showed typical single‐channel behavior for Rb + and Ba 2+ ions, using the patch clamp technique. Thus, channel‐forming activity of a pure polyester has been demonstrated for the first time ( Figs. 1, 3 , and 6 ). Single‐channel activity depends upon the following structural parameters of the 3‐HB derivatives: unprotected OH and COOH groups on the chain ends; chain length ⩾ 16 monomer units; no high ‐molecular‐weight as in P(3‐HB). The results are discussed in view of the Ca 2+ ‐specific channel formed with the P(3‐HP)/Ca · PPi complex from genetically competent Escherichia coli and in view of the ubiquitous occurrence of low‐molecular‐weight P(3‐HB) in prokaryotic and eukaryotic organisms. A simple model for the channel‐causing structure is proposed, based on the proven tendency of oligo‐ and poly(3‐HB) to form ca. 50‐Å thick lamellar crystallites.