Abstract
Copolypeptides with both hydrophilic and hydrophobic side chains, i. e. Poly (Lys, Ala), Poly (Lys, Abu), Poly (Lys, Ser) and Poly (Asp, Ala) were synthesized. Acid-, base-, salt-, and pH-dependent conformational transition 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 conformat ion in a citric acid-NaOH at pH 4.53, while random-coil was mainly observed in a KC1 solution at pH 6.25. Poly (Lys, Ala) was also in the helix in the phosphate buffer solution at pH 6.86, but Poly (Lys) was in the coiled form. Since Poly (Lys, Ser) rarely took the helix conformation, intermolecular hydrogen bonding between hydroxyl groups of the Poly (Lys, Ser)may be involved. Confo rmational change of these copolypeptides is dependent on both pH and coexisting ions.
