Optical rotatory dispersion and nuclear magnetic resonance. Studies of helix coil transitions in poly-L-arginine, poly-L-lysine and histones.

The helixcoil transitions of poly-l-arginine and poly-l-lysine are compared with that of calf thymus histone, using spectroscopic methods. Although poly-l-lysine can be obtained in helical form in water by raising pH or ionic strength, this is not found to be possible with poly-l-arginine. Optical rotatory dispersion data for the synthetic polypeptides indicate sharp transitions when certain organic solvents are added to aqueous solutions. Calf thymus histone by contrast shows a gradual change in helicity as organic solvents are added. The high resolution nuclear magnetic resonance spectra of poly-l-lysine and poly-l-arginine in aqueous methanol mixtures have been obtained. The αCH peak position is found to depend on the polymer conformation and for fully helical poly-l-arginine lies at approx. 6.0.