Shimomura O, Inouye S
Marine Biological Laboratory, Woods Hole, Massachusetts 02543, USA.
Biochem Biophys Res Commun. 1996 Apr 5;221(1):77-81. doi: 10.1006/bbrc.1996.0548.
The photoprotein aequorin emits light in the presence of a trace of Ca2+. The primary structure of the protein indicates the presence of three Ca2+-binding sites, whereas the luminometric titration of heterogeneous natural aequorin with Ca2+ has shown that the light emission takes place by the binding of two Ca2+ ions. In the case of recombinant aequorin, which is more suitable for quantitative studies, the titration with Ca2+ monitored by a Ca2+-sensitive electrode revealed that the photoprotein can bind more than two, most likely three, Ca2+ ions, and the luminometric titration conclusively showed that the luminescence is triggered by the first two Ca2+ ions bound. The affinity of recombinant aequorin for the first two Ca2+ ions, which are essential for light emission, was about 20 times stronger than that for the third Ca2+ ion, which is unrelated to light emission.
光蛋白水母发光蛋白在微量Ca2+存在时会发光。该蛋白的一级结构表明存在三个Ca2+结合位点，而异质天然水母发光蛋白与Ca2+的发光滴定表明，发光是由两个Ca2+离子的结合引起的。对于更适合定量研究的重组水母发光蛋白，用Ca2+敏感电极监测的Ca2+滴定显示，该光蛋白可以结合两个以上，很可能是三个Ca2+离子，发光滴定最终表明，发光是由结合的前两个Ca2+离子触发的。重组水母发光蛋白对发光必不可少的前两个Ca2+离子的亲和力比对与发光无关的第三个Ca2+离子的亲和力强约20倍。
