Excitation of indole-3-acetic acid (an auxin) in a linoleate-lipoxygenase system

The weak luminescence that accompanies the linoleate-lipoxygenase reaction was greatly enhanced by the addition of indole analogues, and especially indole acetic acid. The main emitting species in the indole acetic acid-linoleate-lipoxygenase system was analysed spectrophotometrically in the visible region and ascribed to the transition of excited indole acetate in triplet state to its ground state. Such an excited indole acetate could be generated by transfer of energy from the excited CO2 and excited carbonyl (generated by the linoleate-lipoxygenase reaction) to indole acetate in the ground state, but not by cleavage of the dioxetane analog (positions 2 and 3 on the indole ring).