title: Red light in chemiluminescence and yellow-green light in bioluminescence: color-tuning mechanism of firefly, Photinus pyralis, studied by the symmetry-adapted cluster-configuration interaction method.
abstract: The yellow-green luminescence from firefly luciferase has long been understood to be the emission from enol-oxyluciferin. However, a recent experiment showed that an oxyluciferin constrained to the keto form produced a yellow-green emission in luciferase (Branchini, B. R.; Murtiashaw, M. H.; Magyar, R. A.; Portier, N. C.; Ruggiero, M. C.; Stroh, J. G. J. Am. Chem. Soc. 2002, 124, 2112-2113). The present quantum mechanical/molecular mechanical and symmetry-adapted cluster-configuration interaction (SAC-CI) theoretical study supports the keto-form to be the yellow-green bioluminescence state in luciferase. We give the theoretically optimized structure of the excited state of oxyluciferin within luciferase, which gives luminescence calculated by the SAC-CI method that is close to the experimental value. Coulombic interactions with neighboring residues, in particular Arg218 and the phosphate group of AMP, play important roles in the color-tuning mechanism. Transformation to the enol form is energetically unfavorable in the luciferase environment. The twisted intramolecular charge-transfer (TICT) state is meta stable and would be easily relaxed to the co-planer structure. Further analyses were performed to verify the spectral-tuning mechanism based on the protonation state and the resonance structure of oxyluciferin.
authors.affiliation: Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto-Daigaku-Katsura, Nishikyo-ku, Kyoto 615-8510, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Nakatani
authors.forename: Jun-Ya
authors.initials: JY
authors.lastname: Hasegawa
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nakatsuji
mesh_terms: D000818:Animals; D003116:Color; D048888:Fireflies / Q000502:physiology*; D007211:Indoles / Q000737:chemistry; D008027:Light; D049409:Luciferases, Firefly / Q000737:chemistry*; D049449:Luminescence; D008164:Luminescent Proteins / Q000737:chemistry; D008958:Models, Molecular; D011719:Pyrazines / Q000737:chemistry; D011789:Quantum Theory
chemical_list: D007211:Indoles; D008164:Luminescent Proteins; D011719:Pyrazines; C014730:oxyluciferin; D049409:Luciferases, Firefly