Reassessment of the electronic circular dichroism criteria for random coil conformations of poly(L-lysine) and the implications for protein folding and denaturation studies

The circular dichroism (CD) spectra of poly(L-lysine) in water and ethanediol/water (2:1) solutions in the temperature range -110 to 85 degrees C are presented. The results combined with vibrational CD data are interpreted in terms of a two-state conformational equilibrium with a left-handed trans polyproline II conformation being preferred at low temperatures. The relevance of these studies to the CD criteria for random-coil conformations, the study of helix-coil transitions and protein/peptide folding is pointed out.