Identification of a novel oxidation product from yellow fluorophore in the complex of apoPholasin and dehydrocoelenterazine.

The complex of the recombinant fusion protein of apoPholasin and glutathione S-transferase (GST-apoPholasin) with non-fluorescent dehydrocoelenterazine (dCTZ) (GST-apoPholasin/dCTZ complex) shows yellow fluorescence at 539 nm by excitation at 430 nm. The GST-apoPholasin/dCTZ complex with a fluorophore (dCTZ*) has considerably weak luminescence activity, converting slowly to a blue fluorescence protein with the emission peak at 430 nm. The main oxidation products from dCTZ* for blue fluorescence were identified as coelenteramine (CTM) and an unreported pyrazine derivative, 3-benzyl-5-(4-hydroxyphenyl)pyrazin-2(1H)-one (CTO) that was confirmed by chemical synthesis.