CONFORMATIONAL TRANSITION OF COPOLYPEPTID ES WITH BOTH HYDROPHILIC AND HYDROPHOBIC GROUPS SIDE-CHAINS

Copolypeptides with both hydrophilic and hydrophobic side chains, i.e. Poly(Lys, Ala), Poly(Lys, Abu), Poly(Lys, Ser) and Poly(Asp, Ala) wer e synthesized. Acid-, base-, salt-, and pH-dependent conformational tr ansition of these copolypeptides were compared with those of Poly(Lys) at various buffer solutions by using circular dichroism spectroscopy. Poly(Lys, Ala) was in the helix conformation in a citric acid-NaOH at pH 4.53, while random-coil was mainly observed in a KCl solution at p H 6.25. Poly(Lys, Ala) was also in the helix in the phosphate buffer s olution at pH 6.86, but Poly(Lys) was in the coiled form. Since Poly(L ys, Ser) rarely took the helix conformation, intermolecular hydrogen b onding between hydroxyl groups of the Poly(Lys, Ser) may be involved. Conformational change of these copolypeptides is dependent on both pH and coexisting ions.