Two excited states in aequorin bioluminescence induced by tryptophan modification

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Abstract
The Ca2+‐activated photoprotein, aequorin, contains six tryptophan residues and has a bioluminescence emission maximum at 465 nm. On converting the six tryptophan residues to phenylalanine, the mutant aequorins exhibited varied luminescence activities and spectra, but one mutant, with tryptophan‐86 replaced by phenylalanine, gave a bimodal emission spectrum, with maxima at 455 nm and 400 nm. This result suggests that tryptophan‐86 may be importantly involved in the generation of the product excited state during aequorin bioluminescence.