OPTICAL ROTATORY PROPERTIES OF THE S-SULPHONATE OF THE A-CHAIN OF INSULIN

The optical rotatory dispersion of the S-sulphonate of the A-chain of insulin was studied.[α]_D was found to be-98° and to remain unchanged in the region of pH 5 to 9. 5. The change of λ_c, however, was not parellel (Fig. 1). In 8 M urea [α]_D equalled-106° and λ_c, 198 mμ. It could be tentatively concluded from these [α]_D values that the A-chain behaved as if it were a random-coil.The addition of organic solvents (ethanol, dioxane, and dimethyl sulfoxide) to a solution of the A-chain elicited changes in the optical rotatory dispersion properties whieh, in the case of proteins,would be interpreted as arising from helix formation.The discrepancy between the changes in λ_c and [α]_D with pH pointed once again to the desirability of accumulating more experimental data for the eventual elucidation of the contribution of helical structures to the optical rotatory dispersion properties of peptides.