STRUCTURE AND STABILITY OF INSULIN DISSOLVED IN 1-OCTANOL

Addition of stoichiometric amounts of sodium dodecyl sulfate (SDS), an anionic detergent, to aqueous solutions of insulin produces a SDS-insulin complex which has limited solubility in water. However, the complex displays markedly enhanced solubility in nonaqueous solvents, such as 1-octanol. Concentrations of up to 1 mg/mL of insulin in 1-octanol can be obtained. Using circular dichroism spectroscopy, it was found that insulin maintains its native-like secondary and tertiary structure in 1-octanol. Insulin can be extracted back into an aqueous phase from 1-octanol, again with retention of its native conformation, provided there is sufficient chloride present to displace the bound detergent molecules, The stability of insulin with respect to thermal denaturation is significantly increased, as the T(m) is shifted by 50-degrees-C relative to unfolding in water.