Effect of heavy atoms in bioluminescent reactions.

Bioluminescent reactions of luminous organisms are excellent models for studying the effects of heavy atoms on enzymatic processes. The effects of potassium halides with halide anions of different atomic weight were compared in bioluminescent reactions of the firefly (Luciola mingrelica), a marine coelenterate (Obelia longissima), and a marine bacterium (Photobacterium leiognathi). Two mechanisms of the effects of the halides were examined-the physicochemical effect of the external heavy atom, based on spin-orbit interactions in electron-excited structures, and the biochemical effect, i.e. interactions with the enzymes resulting in changes of enzymatic activity. The physicochemical effect was evaluated by using photoexcitation of model fluorescent compounds (flavin mononucleotide, firefly luciferin, and coelenteramide) of similar structure to the bioluminescence emitters. The bioluminescent and photoluminescent inhibition coefficients were calculated and compared for the luminous organisms to evaluate the relative contributions of the two mechanisms. The biochemical mechanism was found to be dominant. Hence, the bioluminescent reactions can be used as assays to monitor enzyme inhibition, in metabolic processes, by Br or I-containing compounds.