Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment and General Theory 2012-07-19

Comparative study of the photoprotolytic reactions of D-luciferin and oxyluciferin.

Yuval Erez, Itay Presiado, Rinat Gepshtein, Luís Pinto da Silva, Joaquim C G Esteves da Silva, Dan Huppert

Index: J. Phys. Chem. A 116 , 7452-7461, (2012)

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Abstract

Optical steady-state and time-resolved spectroscopic methods were used to study the photoprotolytic reaction of oxyluciferin, the active bioluminescence chromophore of the firefly's luciferase-catalyzed reaction. We found that like D-luciferin, the substrate of the firefly bioluminescence reaction, oxyluciferin is a photoacid with pK(a)* value of ∼0.5, whereas the excited-state proton transfer (ESPT) rate coefficient is 2.2 × 10(10) s(-1), which is somewhat slower than that of D-luciferin. The kinetic isotope effect (KIE) on the fluorescence decay of oxyluciferin is 2.5 ± 0.1, the same value as that of D-luciferin. Both chromophores undergo fluorescence quenching in solutions with a pH value below 3.