The effect of cytochrome-c on AOT/water/isooctane reverse micelles was studied by differential scanning calorimetry. We measured the ice-to-liquid latent heat of water pools in reverse micelles containing cytochrome-c. We found that AOT-bound water molecules are released by cytochrome-c, accompanied by the enhancement of water solubilization in reverse micelles. A possible mechanism is proposed to interpret the observed protein effect.