No evidence for non-resonant optical frequency-induced effects on the intrinsic fluorescence of adenosine-5′-triphosphate and the kinetics of the firefly luciferin–luciferase reaction

A paper by Amat et al. [2] reported that the ATP-driven oxidation of luciferin to electronically excited oxyluciferin catalyzed by luciferase was accelerated when ATP was priorly irradiated at non-resonant optical frequencies (NROF) at 635 and 830 nm. In another paper by Amat et al. [3], increased fluorescence intensities of ATP–Mg complexes, which showed lower fluorescence than ATP when excited at 260 nm, were reported in consequence of concomitant NROF irradiation (i.e., 655 and 830 nm). It was postulated that NROF-induced electric field changes may alter the charge distribution in ATPʹs phosphate chain, resulting in lowering of the activation energy of its terminal phosphate. Here we use spectrofluorometry to further investigate this hypothesis. The effect of NROF (at 632.8 nm) on the intrinsic fluorescence of non-complexed and Mg-chelated ATP in aqueous solution and the influence of NROF (514.5 nm and 632.8 nm) on the rate of the luciferin–luciferase reaction was studied. We found that neither the intrinsic fluorescence of ATP nor its biochemical behavior during the firefly luciferin–luciferase reaction was affected by laser irradiation with NROF. Consequently, no evidence was found supporting the postulation that NROF-induced alternations on the charge distribution of the phosphate chain affect the reactivity of ATP.