Partially Helical Conformation of Hemoglobin in Aqueous 2-Chloroethanol

The hemoglobin molecule lost part of its α-helical structure when its tertiary structure was disrupted by the addition of 2-chloroethanol. The molecular weight was reduced to one-fourth. The observed decrease in helix content was directly in parallel with the decrease in the magnitude of the Cotton effect in the Soret absorption band. This phenomenon was attributed to the dependence of the secondary structure formation on the interaction between peptide chains and the prosthetic heme group. In 20 to 50% of aqueous 2-chloroethanol, the hemoglobin molecule assumes a partially helical random coil, and it was characterized by the measurement of intrinsic viscosity, by the effect of temperature on its structure, and by fast deuterium exchange of the amide hydrogens. In aqueous 2-chloroethanol solution of more than 50%, the fraction of helix in the peptide chain increased along with the concentration of 2-chloroethanol. This was found to be a common phenomenon for denatured proteins of various kinds.