Luminescence of a bacterial luciferase intermediate by reaction with H2O2: the evolutionary origin of luciferase and source of endogenous light emission

Abstract The bacterial luciferase reaction was shown to emit light in the presence of hydrogen peroxide (H 2 O 2 ) instead of aldehyde. Although the light intensity was weaker than that with an aldehyde, the bioluminescence emission spectrum of the luciferase reaction ( λ max 495 nm) with H 2 O 2 closely agreed with that using a long chain aliphatic aldehyde (decanal). It was also found that the chemiluminescence of reduced or unreduced FMN with H 2 O 2 was enhanced by peroxidase. Light emission in the luciferase reaction with H 2 O 2 is attributed to a catalase-like reaction, in which the abstraction of one atom of oxygen from intermediate II (luciferase-bound FMNH-OOH) by H 2 O 2 leads to the formation of excited hydroxide (E-FMNH-OH∗), H 2 O and O 2 . Since H 2 O 2 is formed in the spontaneous breakdown of intermediate II in the absence of aldehyde, the reaction of this H 2 O 2 with intermediate II can explain the origin of endogenous (non aldehyde) light emission. In the presence of luciferase, intermediate II can be formed both from FMNH 2 and oxygen, and by the reaction of H 2 O 2 with FMN. The functional origin of the bacterial luciferase is postulated to be a FMN-dependent non-heme catalase which scavenges H 2 O 2 , concomitant with weak light emission. Prior to the association of luciferase genes ( lux AB ) with the aldehyde synthesis genes ( lux CDE ), forming the lux operon in luminous bacteria, the genes may have been expressed independently such that the bacteria lacked a high level of light emission.