Effect of sodium dodecyl sulfate, acid, alkali, urea and guanidine hydrochloride on the circular dichroism of alpha-globulin of Sesamum indicum L.

The circular dichrotic spectra of alpha-globulin have been obtained under various solution conditions of sodium dodecyl sulfate, acid, alkali, urea and guanidine hydrochloride. The protein in phosphate buffer pH 7.4, 0.2 M has about 25% beta-structure and 5% alpha-helix, the rest being aperiodic or irregular structure. Sodium dodecyl sulfate induced more alpha-helical structure in the protein. The protein had nearly 20% alpha-helix at 1 X 10(-2) M SDS. At extreme acid or alkaline pH, the protein had no alpha-helix with beta-structure decreasing with further extremes of pH. The protein is represented by 100% aperiodic structure in 6.6 M urea and in 6.0 M guanidine hydrochloride solutions. The above results are discussed in view of some of the earlier results with regard to the association-dissociation and denaturation behavior of alpha-globulin under various solution conditions.