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Aqueous solutions can be solubilized in organic solvents with the help of reverse micelles formed by bis(2-ethylhexyl) sodium sulfosuccinate (AOT), a negatively charged surfactant. The physicochemical properties of the proteins solubilized in the reverse micelles can be modulated by varying the amount of water present in the system. We studied the unfolding transition of globular proteins (ribonuclease, cytochrome c, lysozyme) in the AOT/isooctane micellar system by differential scanning calorimetry (DSC). The thermodynamic parameters associated with the transition were studied as a function of the micellar critical parameters and system composition. The DSC thermogram of a protein micellar solution showed a single sharp transition that can be attributed to a cooperative unfolding process of the protein structure. The Tm, AH, AS, and AG of the unfolding process calculated from the thermograms were strongly dependent on the amount of water present in the system. Protein micellar solutions at low water content were remarkably stable as a function of time.

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