Optical rotatory dispersion and the conformation of human γ-globulin

Abstract

Optical rotatory dispersion has been used as a means of studying conformational changes in human [gamma]-globulin under various environmental conditions. The effects of protein concentration, ionic strength, pH, urea and 2-chloroethanol have been described. The dispersion data were abnormal when compared with those of albumin and it was impossible to explain the results on a simple helix-coil transition involving increase or decrease of intramolecular hydrogen bonds. The results are explained on the basis of compensating structures within the molecule, the particular structures suggested being the right-handed [alpha]-helix and [beta]-form. The effect of urea is to cause a decrease in both structures. Low concentrations of 2-chloroethanol produce a decrease in [beta]-form by a lessening of hydrophobic forces; high concentrations of 2-chloroethanol cause an increase in [alpha] -helix and [beta]-form through increased hydrogen-bonding. The structure of the molecule is discussed in the light of these and earlier findings.