Conformation of Poly(L-lysine) and Poly(L-ornithine) in α, ω-Type Surfactant Solutions

Circular dichroism spectra of poly(L-ornithine) and poly(L-lysine) were measured in disodium α, ω-alkanedisulfate [Na 2 C n H 2 n (SO 4 ) 2 ( n = 8,10, 12,16) (RDS)] solutions in the presence and absence of NaCl at various tempera tures. The 1,16-RDS induced an α-helix in poly(L-ornithine) and a β-sheet in poly(L-lysine) at 30°C, while 1,10- and 1,8-RDS induced no conformational change in either polypeptide even at a surfactant concentration where turbid ity appears. Although 1,12-RDS induced no conformational change in poly(L- ornithine), it does induce α-helix, β-sheet or stepwise transition from coil to β-sheet and then to α-helix with increasing 1,12-RDS concentration, depending on the temperature and concentration of added NaCl. The plots of α-helix con tent against temperature at various concentrations of 1,12-RDS are quali tatively consistent with the dependence of α-helix content on the size growth of surfactant cluster bound to polypeptide.