Membranes solvent-cast from the triblock copolypeptide poly (y-benzyl-L-glutamate)x -poly( L-leucine)y-poly (y-benzyl-L-glutamate)x, in which the mole ratio of the constituent blocks was properly tailored, displayed a mesophase structure comprised of cylindrical domains of poly(y-benzyl-L-glutamate) in a continuous matrix of poly(L-leucine). Further, the poly (y-benzyl-L-glutamate) domains formed transmembrane channels that connected the two faces of the membrane. These channels were rendered

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... drophilic by saponifying the benzylglutamate groups to glutamic acid groups. While the hydrophilization process increased the water content of the poly(L-glutamic acid) domains, these domains retained their size and shape even when the pH and ionic strength of the aqueous medium was sufficient to ionize all the glutamic acid groups in the domain. The saponified triblock copolypeptide membrane described above generated spontaneous electrical pulses under a salt concentration gradient. Current-voltage curves of the saponified membranes were sigmoidal in a salt solution over pH 3.5 and below 10-2 M, and hysteresis appeared. An electrical current also induced oscillation of membrane potential across the saponified membranes. The mechanism of the spontaneous oscillation is interpreted in terms of conformational change (a-helix--random coil) of the poly(L-glutamic acid) block chains in the saponified membranes in relation to the membrane structure.