Structure of Bovine αs-Casein

The secondary structure of bovine αs-casein and chemically modified αs-casein in various solvents was investigated by infrared absorption spectrum and optical rotatory dispersion measurements. Amino groups of αs-casein were either succinylated or acetylated, and carboxyl groups were either methylated or ethylated. Acetylated- and ethylated-αs-caseins are insoluble in water. Water-soluble samples have unordered structure in water. In organic solvents, such as 2-chloroethanol and ethylene glycol, they have about 50% α-helical fraction. On the other hand, it was found that methylated-αs-casein had two infrared absorption peaks centered at 1625 and 1643 cm−1 in D2O-CH3OD mixed solvent. This fact may be connected with the presence of β-structure. In the case of solid film of this sample, cast from solution containing CH3OH, the presence of β-structure was indicated, too. The authors attempted to explain the formation of β-structure in methylated-αs-casein in terms of the electrostatic interactions due to the d...