The relative rate of aequorin regeneration from apoaequorin and coelenterazine analogues.

The regeneration of an active semi-synthetic aequorin, from apoaequorin produced in cells and a coelenterazine analogue, is a key step in measuring Ca2+ in the cells. The relative rates of the regeneration of semi-synthetic aequorins from apoaequorin and 28 synthetic coelenterazine analogues were compared. The results indicated that the rate is strongly influenced by the analogues used. The regeneration of ordinary aequorin with normal coelenterazine was relatively fast (50% regeneration in 22 min), whereas the rates of regenerating semi-synthetic aequorins with coelenterazine analogues varied widely, and all were slower than that of regenerating ordinary aequorin, except for e-type coelenterazines (containing an extra ethano group). The regeneration with e-type coelenterazines was significantly faster, indicating the possible superiority of e-type analogues in the intracellular regeneration of aequorin, especially when an increased sensitivity to Ca2+ is needed.