The Secondary Structure of αs-Casein

CD spectrum of αs-Casein which is a major component of bovine casein, showed a small shoulder near 225 nm, This shoulder disappered by the addition of guanidine hydrochloride or urea. It is considered that the shoulder is dependent on the intramolecular interaction of CO-NH of αs-casein from solvent perturbation difference spectra by 20% glycerol. Applying formulas proposed by Chen et al. for calculation of secondary structure constituent, ratios of α-helix, β-from and unordered form were 1, 1, and 8, respectively. The ratio of CO-NH contributed to secondary structure was 20 %, and agreed very colsely with that obtained by difference spectra.