Conformational Change of Poly(L-lysine) by Sodium Octyl Sulfate as Studied by Stopped-flow Circular Dichroism Method

Abstract Circular dichroism (CD) studies were made on the conformational changes of poly(l-lysine) (PLL) induced by sodium octyl sulfate (SOS). The conformation of PLL has a negative double maximum characterizing the α-helix in 4.0–6.0×10−3 mol/dm3 SOS solutions. At a higher concentration of SOS, PLL takes the β-structure, the random coil remaining below it. These conformational changes were followed by measuring ellipticities at 192, 207, and 221 nm according to a CD stopped-flow method. The rate constant was ca. 2.7×10−1 s−1 for the coil-helix transition, the transition rate from coil to β-structure being high depending on SOS concentration. The β-structure was attained by adding a small amount of 1-octanol to the α-helical PLL in 5.0×10−3 mol/dm3 SOS. The effect of the surfactant on the triphasic conformation changes is discussed in terms of hydrophobic environment.