Although native aequorin is highly susceptible to inactivation, apoaequorin is highly resistant to various processes of denaturation. Apoaequorin was inactivated only partially at a temperature of 95 degrees C or by treatments with 6 M-urea, 4 M-guanidine hydrochloride, 1 M-HCl and 1 M-NaOH. It was nearly completely inactivated in 85% ethanol or by heating at 95 degrees C in 2 M-(NH4)2SO4, but over 50% of apoaequorin activity was restored in both cases merely by dissolving the coagulated protein in 4 M-guanidine hydrochloride. In the reconstitution of aequorin, partially inactivated apoaequorin yielded more aequorin than expected from the activity of the partially inactivated apoaequorin used, suggesting that the process of reconstitution promotes the renaturation of denatured apoaequorin.
