SPONTANEOUS OSCILLATION OF THE ELECTRICAL MEMBRANE-POTENTIAL IN TRI-BLOCK COPOLYPEPTIDE MEMBRANES COMPOSED OF L-GLUTAMIC ACID AND L-LEUCINE

A membrane produced from a tri-block copolypeptide composed Of poly(L-glutamic acid) as outer segments and poly(L-leucine) as an inner segment spontaneously generated electrical pulses under a concentration gradient of KCl in the absence of any external current, voltage, or pressure. At lower KCl concentrations the current-voltage curves of the membrane were sigmoidal, and hysteresis appeared. This result suggests that the membrane can have two different resistance states which are related to alpha-helix and random-coil conformations of the poly(L-glutamic acid) chain. According to the circular dichroism and FT-IR spectra of the membrane, in the higher resistance state the poly(L-glutamic acid) chains exhibit random-coil structure, while in the lower resistance state the chains exhibit alpha-helix structure. The oscillation mechanism of the membrane potential may be explained by a periodic change of KCl permeability of the membrane, which is induced by a periodic change in the conformation between alpha-helix and random-coil structure of the poly(L-glutamic acid) chain. The frequency of the electrical pulses was pH dependent and showed a maximum between pH 3 and pH 4.