Coelenterazine & Synthetic Analogues

• Coelenterazine and coelenterazine derivatives complex with aequorin to offer luminescent Ca²⁺ readout in cells
• Luminescent readout eliminates common cellular fluorescence interference issues
• Highly sensitive, allowing measurement of Ca²⁺ concentrations from 0.1 µM to 100 µM levels
• Invitrogen offers a portfolio of 6 Coelenterazine proteins including 5 derivatives offering differing Ca²⁺  affinities and spectral emissions
• Native Coelenterazine as well as all 5 analogs are available together in a Sampler Panel for comparison and evaluation
   

Aequorin is a calcium-sensitive bioluminescent protein from the jellyfish Aequorea victoria that has been used extensively as a microinjectable calcium indicator in cells.  The aequorin complex comprises a 22,000-dalton apoaequorin protein, molecular oxygen and the luminophore coelenterazine (Figure 1). When three Ca²⁺ ions bind to this complex, coelenterazine is oxidized to coelenteramide, with a concomitant release of carbon dioxide and blue light (Figures 2 and 3). The approximately third-power dependence of aequorin's bioluminescence on Ca²⁺ concentration gives it a broad detection range, allowing the measurement of Ca²⁺ concentrations from ~0.1 µM to >100 µM.

In addition to native coelenterazine (C-2944), we offer five derivatives of coelenterazine designated cp, f, h, hcp and n by Shimomura and colleagues that confer different Ca²⁺ affinities and spectral properties to the aequorin complex (Table 1).  Like native coelenterazine, these five derivatives can be used to reconstitute the aequorin complex both in vivo and in vitro.  Aequorin reconstituted with coelenterazine hcp shows very favorable characteristics, including a fast response to binding Ca²⁺ and the highest luminescence quantum yield of these five coelenterazine derivatives. Aequorins containing the cp, f or h form of coelenterazine are reported to exhibit relative intensities that are 10–20 times that of apoaequorin reconstituted with native coelenterazine.  Knight and co-workers reported that aequorin reconstituted with coelenterazine h is more sensitive to Ca²⁺ than is the native complex, thus providing a valuable tool for measuring small changes in Ca²⁺ concentrations.  Coelenterazine n is reportedly the most useful low-sensitivity coelenterazine, producing an apoaequorin/coelenterazine complex that exhibits 10,000-fold lower luminescent intensity than the apoaequorin/coelenterazine hcp complex.

Table 1.

1. Coelenterazine complexes with apoaequorin emit calcium-dependent bioluminescence. Bioluminescence emission maxima (relative intensity at 100 nM Ca²⁺) are as follows: C2944, 466 nm (1); and C6780, 466 nm (16).
2. Do NOT dissolve in DMSO.
3. Aqueous solutions of coelenterazine (>1 mM) can be prepared in pH 7 buffer containing 50 mM 2-hydroxypropyl-β-cyclodextrin.