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 segme nt spontaneously generated electrical pulses under a concentration gra dient of KCl in the absence of any external current, voltage, or press ure. At lower KCl concentrations the current-voltage curves of the mem brane were sigmoidal, and hysteresis appeared. This result suggests th at the membrane can have two different resistance states which are rel ated to alpha-helix and random-coil conformations of the poly(L-glutam ic acid) chain. According to the circular dichroism and FT-IR spectra of the membrane, in the higher resistance state the poly(L-glutamic ac id) chains exhibit random-coil structure, while in the lower resistanc e state the chains exhibit alpha-helix structure. The oscillation mech anism of the membrane potential may be explained by a periodic change of KCl permeability of the membrane, which is induced by a periodic ch ange in the conformation between alpha-helix and random-coil structure of the poly(L-glutamic acid) chain. The frequency of the electrical p ulses was pH dependent and showed a maximum between pH 3 and pH 4.