Circular dichroism of erythrocyte membrane glycoproteins.

The circular dichroism spectra were obtained for purified equine, human and bovine membrane glycoproteins, which have 40, 55 and 70% carbohydrate, respectively. The spectra in aqueous buffer show similar shapes, maxima and minima but somewhat different peak amplitudes. Analysis of the spectra indicated that the glycoproteins can be pictured as existing primarily in an unordered form in dilute aqueous buffer with small amounts of alpha-helix (13-23%) present. In 2-chloroethanol, a helix-promoting solvent, the amount of alpha-helix is increased to 60-70%. The glycoproteins underwent denaturation in guanidine hydrochloride, although evidence of some residual structure did remain. The spectra of the glycoproteins change relatively little on going from aqueous buffer to dodecylsulfate solutions. Removal of 60% of the sialic acid does not induce significant conformational alterations. The anomalous behavior of the glycoproteins during molecular weight determinations does not appear to be related primarily to conformational restrictions on the polypeptide chain.