Differences in stability of recombinant apoaequorin within subcellular compartments.

Recombinant acquorin is widely used as an intracellular Ca2+ indicator within live cells. Our data shows that recombinant apoacquorin was unstable within the cytosol, with a half life of approximately 20 minutes. Targeting of the protein to subcellular organelles resulted in an increase in stability which may be due to either stabilisation of the photoprotein structure or the absence of the relevant proteases within the organelles. When the apoprotein was reconstituted with the prosthetic group coelenterazine, there was a substantial increase in it's half life in the cytosol. We propose that this variable stability makes acquorin an ideal reporter of gene expression.