Constructing the Mechanism of Dinoflagellate Luciferin Bioluminescence Using Computation

Dinoflagellateluciferin bioluminescence is unique since it doesnot rely on decarboxylation but is poorly understood compared to thatof firefly, bacteria, and coelenterata luciferins. Here we computationallyinvestigate possible protonation states, stereoisomers, a chemicalmechanism, and the dynamics of the bioluminescence intermediate thatis responsible for chemiexcitation. Using semiempirical dynamics,time-dependent density functional theory static calculations, anda correlation diagram, we find that the intermediate's functionalgroup that is likely responsible for chemiexcitation is a 4-memberring, a dioxetanol, that undergoes [2 & pi; + 2 & pi;] cycloreversionand the biolumiphore is the cleaved structure. The simulated emissionspectra and luciferase-dependent absorbance spectra agree with theexperimental data, giving support to our proposed mechanism and biolumiphore.We also compute circular dichroism spectra of the intermediate'sfour stereoisomers to guide future experiments in differentiatingthem.