Imidazole-assisted catalysis of luminescence reaction in blue fluorescent protein from the photoprotein aequorin.

Blue fluorescent protein from the calcium-binding photoprotein aequorin (BFP-aq) is a dissociable complex of Ca(2+)-bound apoaequorin and coelenteramide, and is identified as a luciferase that catalyzes the oxidation of coelenterazine by molecular oxygen to emit light. Based on the chemical luminescence of coelenterazine oxidation by an acid-base mechanism, we found that the luminescence activity of BFP-aq was stimulated by imidazole at concentrations of 30-300mM with coelenterazine and its analogues. The kinetic analyses indicate that imidazole has no effect on the binding affinity of coelenterazine to BFP-aq and may act as a catalytic base, accepting a proton from the -NH- group of coelenterazine and stimulating luminescence activity.